AWS emulator | Hacker News Reader

AWS emulator

github.com

876 pointssuper_linear240 comments

https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent...

Pass rates from the release's > Thousands of Feels more like a science ??? You and I are the customers. [1] https://www.allthingsdistributed.com/2026/11/aws-emulator-an...

Open articleView on HN

Skeptical of using because it's not clear whether this was just an exercise or a real product they are going to ship and maintain.

Floci[0] has been great for me. Use the Testcontainers[1], too.

Bonus: works for GCP and Azure, too (so far have only used in limited capacity, though).

[0] https://floci.io/

[1] https://testcontainers.com/modules/floci/

It’s a real product that we plan to maintain.

Nothing personal, but unless you can link us to a public announcement made by Amazon, your statement is worth less than nothing.

Official statements made by a company are still poor representations of their current business plans, and don't mean anything 3 months later (no matter how much they pinky promise). But a HN post isn't even that.

https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent... ?

GP statement still stands, actually being strengthened. This blog post doesn't even mention nor seems to care about maintainability or long-term support or anything that users will care about. Only talks about how cool the team is and how amazing they're at using AI, multi-agent workflows, and this kind of bs. It's funny how author talks so much about testing when they themselves also boast how they haven't written or reviewed any of the code.

Also doesn't mention any benchmarks or compatibility matrix.

This feels like table stakes for an emulator.

I don’t take it personally; I realize you don’t know me, and a sentence on HN isn’t much of a guarantee.

That said, it’s been announced publicly here: https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent...

Additionally Swami, our SVP of AI blogged about it separately and our CTO is tweeting about it - which is more than a number of products get in terms of coverage.

I didn't mean announcing the tool, I meant an announcement committing to the maintenance/support that users like the GP poster were looking for. My bad on describing that clearly, I'm gonna get clowned on in the comments and I'm not turning this around.

I understood what you meant. I was just trying to add evidence to support my claim that it was a real product and would be maintained. And yeah, votes on comments can be fickle.

I think one thing that concerns many people is that this looks like AI slop, which it clearly is according to the blog post.

I think this is a super interesting direction, but how can we trust the accuracy of this simulator? Agentic loops are great and all, but they can still miss plenty of things.

Or maybe a better question: where is the accuracy of this simulator going to be guaranteed enough that we should trust it?

To me, something like this is actually what vibe coding thrives the best at; tight, looped, easily verifiable, test-driven dev work. In fact, this is probably the field it can do with little or no intervention, if you're willing to waste tokens.

Is it? How is it verified that this catches all the potential edge cases of interacting with AWS? Or is handling all the edge cases of AWS not in scope?

Like, what am I actually getting here? Is it just happy path operations being correct here?

For real edge cases, it will be like any other software. Users get to be the guinea pigs and report bugs as they find them.

Hopefully AWS has had enough internal guinea pigs before they published this!

In the near future, every case will be a real edge case and every one will be a guinea pig.

The border between AWS and AWS emulator becomes fuzzy. And the users of AWS will be agents as well. A completely offline emulator will save a lot of resources and could be a great training ground for more focused (offline) models.

Back in the day, we assumed that when a major company open sourced code, that code would have problems. We invented all these things like ‘issues’ to deal with this.

It has its official document page: https://docs.aws.amazon.com/emulator/latest/userguide/gettin... and it lives in https://github.com/aws/ org. I think AWS is pretty committed.

Until the plan changes, which at some point, it will. Comment is still appreciated for what it is.

Edit: Comment is in the spirit of "it gets tiring to build on sand which is at the whims of corporate management folks far disconnected from the actual work." If someone is asserting "this will stick around," words are insufficient, words are free. Show me the contract, show me the penalties for failure to abide by the assertion.

I mean isn't that true for every single thing made by anyone? In that case what more do you want from them?

Except for things they make: forever maintained forever.

A bit more polish for a public facing artifact from a multi-billion dollar org with armies of engineers and big token budgets.

The Copilot CLI https://aws.github.io/copilot-cli/ you can feel polish and pride of the team that built this, as an example.

As someone who used QLDB as a WORM audited log for a financial system, and ran AWS classes that used Cloud9, they do depricate.

Not many, and not often but it is annoying.

This is an Amazon product, not a Google product.

The two have different failure modes.

Google builds up a product over time and abandons it. This is annoying for long term adopters.

AWS has a habit of throwing a bunch of products at the wall, but only bothering to maintain & build up a few of them. This is annoying for early adopters.

Azure on the other hand. Will throw products out, ensure they are never consistent with other offerings on their platform, and then deprecate it from under you while promoting the same thing with a new name.

This is annoying for everyone.

And Azure will send you an email every day about how you need to migrate X to Y without any way for you to know where those instances are or how to find them.

I think there was some truth in this in the early days of Azure (and all clouds) as the companies were looking to work out what cloud services were really needed. I don't see this as much any more though esp when a services makes it to GA they have published commitments for service availability and API compatibility. (I was in Azure for 10+ years so definitely let me know if you disagree)

Yeah I disagree. First of all, Azure is mostly garbage so avoid it if you can. Second of all, Azure deprecation follows Microsoft's general policy of deprecation which is The Fadeaway Policy. Don't publish anything publicly about it, gut the team to go work on something else, transfer the service to be one of 6 dozen other services some random offshore team is "maintaining", experience enough outages and trouble and during every support call they nudge you to move to something else, but the service is "totally not deprecated" because we haven't gotten a memo that says that, but we're only doing "security" fixes now. wink wink, nudge nudge.

Fine to disagree - but it would be better to share real insights rather than just blanket statements. Sounds like you have had some bad experiences - maybe you could share more?

Let me quickly compile a list of the last 700 failing bicep deployments with an “Internal Service Error” or No capacity errors along the all the no-op idempotent puts that take 30+ minutes for some reason, the broken networking system all up, the constant support advise to move to different regions, except half the things you use are not in that region, or the constant advice to just delete everything and start again or the half docs half marketing fluff docs. Azure only exists because large enterprise looks at a list of checkboxes before signing a contract. No reasonable person should ever use that garbage unless you’re offered deep discounts to do so, and even then, limit your usage to things you can migrate easily whenever the discount expires.

Yup I hear you with bicep. Post Microsoft I've used either Terraform or Pulumi. Sorry to hear about the other issues.

To be fair, that's Microsoft in general

Amazon team killed the Copilot CLI[0] which I thought was the single best thing they ever did for AWS infra. Made it tolerable to deploy on AWS; still salty about this one.

[0] https://aws.github.io/copilot-cli/

Yes, we are still struggling with a good replacement. The way they handled this - from steady release cadence to complete stop with no info at all but just speculations makes me very reluctant to adopt AWS maintained projects.

Why would you say this? AWS are notorious for maintaining things.

You're certainly not wrong. But in the wake of Localstack's changes, the landscape has been full of slopware and low trust anyway. I don't think this is worse, for now at least.

"Things change over time" that is how the linear passage of time tends to work, yes.

Is there anywhere I can find a matrix of what services are emulated and how complete that emulation is? I tried the docs but just ended up going round in circles.

If its up to this emulator to keep track of changes in Services APIs this is doomed to fail.

I believe AWS already autogenerates their API clients (e.g. boto3) based on some authoritative internal service api spec so I imagine that spec could be used upstream of this tool as well.

But their auto generated API clients don't have the invariant baked into them, which makes them very rough to use in say Rust.

They'll have something like this:

    MySchema: { enum: [foo, bar] } { enum: [quz, qux] } { enum_member: { const: bar } } } [enum_member_2] } in schemas, this is merely defined in prose around the documentation.So your Rust API is full of Option, and it gets really annoying when you're testing things like say Bedrock, which takes 10 minutes, and then fails because what you submitted 10 minutes before doesn't match their schema.
I understand this can be fixed by reading the documentation in more detail, but it has gotten so verbose, and sometimes you just want to start something.

Not internal. Open sourced: https://github.com/aws/api-models-aws

Yeah whatever they did internally to get service teams to actually adopt AWS Config ~5 years ago needs to happen here or it’s going to get stuck with marquee services and that’s it.  Especially given this is a much much larger ask of each service.

AWS Config already doesn’t support some pretty important things

Agreed but it used to be way way worse.

AWS has lots of unfunded mandates like this and they historically just depended on bleeding the souls of engineers and managers to get done.I suspect this is built by agents through bleeding the soul of GPUs until it gets too expensive (unfunded mandates are free after all on the OP1/2). Then it just decays into the place all good PR/FAQs decay once their sponsors are promoted, burned out, or are laid off.

There are many AWS services.  Simply offering an alternative to a few of the most used could be a good business.  It doesn't have to cover all AWS in all release versions, just enough to get and hold some clients

This wasn't clear to me, either.

Sort of.  The releases page leads you to a massive blob of json with all the compatibility tests and scores.Edit: The current one: https://github.com/aws/aws-emulator/releases/download/v1.0.3...
You can get some idea if the product name is unique enough with <ctrl-f> and looking at each of the related test scores.

Asked a clanker to correlate the test data (link in parent) with: content.com/aws/aws-emulator-evaluation-suite/refs/heads/main/manifest.jsonl" target="_blank" rel="nofollow noopener noreferrer">https://raw.githubusercontent.com/aws/aws-emulator-evaluatio...And output something meaningful for some of the more popular services:
  Service            Tests  All  Happy  Reject  Ctrl  Data  Solo  Integ  Wire#  Wire% ---  -----  ------  ----  ----  ----  -----  -----  ----- 91%   92%   72%   89%    59%     24    62% 79%   79%   42%   79%     0%     21    52% 64%   72%   68%   83%    67%     75    84% 69%   81%   68%   97%    36%     69    84% 53%   69%   67%   73%    65%     68    76% 61%   62%   65%   82%    53%    243    62% 55%   62%   68%   75%    65%     39    69% 67%   61%   68%   94%    62%     29    45% 65%   66%   72%   79%    57%     26    77% 66%   82%   36%   75%    33%    193    64% 57%   61%   57%   83%    51%    296    68% 63%   70%   46%   71%    41%    190    22% 59%   77%   41%   75%    43%    200    73% 59%   75%   48%   77%    40%     44    30% 59%   62%   53%   69%     0%     49    67% 51%   66%   53%   77%    36%    152    55% 75%   67%   49%   87%    27%     74    65% 44%   63%   50%   62%    54%     25    44% 50%   60%   34%   78%    41%    228    57% 59%   78%   20%   65%    17%     19    47% 54%   71%   47%   78%    41%    185    59% 52%   70%   29%   59%    50%     98    48% 52%   74%   38%   73%    33%    107    27% 52%   65%   10%   59%    38%     55    62% 55%   66%   32%   69%    40%    155    43% 42%   58%   48%   48%    54%    171    42% 52%   62%   23%   62%    34%    118    44% 47%   53%   52%   47%    57%     50    46% 46%   56%   30%   57%    34%     22    50% 47%   55%   19%   58%    30%    111    63% 45%   54%   35%   51%    31%     99    28% 49%   54%    0%   47%    17%     27    41% 36%   39%    5%   44%    32%    429    33% 31%   30%   40%   78%    24%   2161     3% 35%   54%    1%   44%     0%     91    13% 27%   27%   25%   26%    30%    175    11% 15%    7%   28%   16%    37%     37     0% 23%   19%   18%   21%    20%     89    16% scores.json (commit 7753983), joined with the eval suite's manifest.jsonl. Tests = behavioral checks touching the service. All = overall pass rate. Happy/Reject = valid requests vs. requests AWS should refuse. Ctrl/Data = control plane vs. data plane. Solo/Integ = single-service vs. multi-service checks. Wire# / Wire% = count and pass rate of recorded request/response replay tests (a test passes only if every call matches).Edit: Also worth a look: https://ministack.org/blog/aws-emulator

I mock (ask Claude Code to make something run in a container) my own AWS services today for CI and development. I'm excited to learn more about how AWS uses it and hopefully use this for CI and development.

Any chance it will be able to spawn actual containers in the future?

That is pretty much the key thing IMO. It needs to be able to run our actual code, locally, with fairly high fidelity to the real thing in terms of behavior.For the AWS people behind this, it means going the extra mile(s), with a level of care and depth that you typically mostly see within great startups. Perhaps agentic coding will enable AWS to reach this, perhaps it will stay relatively abstract.

Not to be rude, but your profile doesn't list who you are in relation to AWS.

Good! Been waiting for a first party thing like this.It’s actually interesting that such a thing exists. It’s in Amazon’s interest that the only way to test a lot of services is to have a test environment in AWS.

Okay I've asked for this product for literally years on a cadence of every 18 months, so I'm very thankful to hear this.

>> Skeptical of using because it's not clear whether this was just an exercise or a real product they are going to ship and maintain.> It’s a real product that we plan to maintain.
29,684 commits in a repository less than a month old does not instill confidence in this being a "real product."  That is roughly 1,000 accepted commits per day.

Planning to maintain probably means planning to continue telling Claude to maintain it

And that’s probably something that AI will be really good at.

In my experience Floci has been the epitome of vibe coded - huge amount of changes, with things breaking randomly between releases. Moved away from it as soon as I could. Still better than Localstack :)I didn't have a good experience with test containers, but perhaps it'd work better with fast starting containers. We run our test fixture with compose, and have the tests manage their data in isolation - so we don't pay the startup penalty in our test suites.
I think I'd trust this project at least as much as Floci. Embedded Rust mode also looks very interesting for us.

I only use Testcontainers with "explicit" tests (do not run by default in CI; must be run explicitly).  This lets agents exercise the integration with a realistic fake locally, but does not incur the cost in CI nor for any dev unless they run it explicitly (usually also with a category so it's explicit + category filter)

It has an official documentation on the AWS website, why would you assume it's not a real product? Because it was launched recently?

No docs site linked on the GH.  3 weeks old.  Blog post talks more about the process than the tool and opens with:
    > How we built the agents that built AWS Emulator autonomous AI agents wrote every line of code in AWS Emulator, a new local emulator for AWS now available for download. experiment than a product from that announcement.Doesn't feel like a real product.  But I also didn't look very hard for docs; I kind of expect it to be linked on the GH in the site and have a nice `llms.txt` for me to give to my agents.

> No docs site linked on the GH.??? It's in bold just before the "Quick start" section

There's a right way and a wrong way to assign a website URL in GH.The team didn't even take the time to review these small details of the repo, you know, by editing the repository details to place the docs URL there.
I mean, I don't know about you, but I feel like I still like to see people care about the stuff they produce and missing something as basic as the repo website URL in GH settings shows a lack of polish and love.

Your comment comes off very dismissive and in poor taste.> Doesn't feel like a real product. But I also didn't look very hard for docs
You should try, they're there.
> I kind of expect it to be linked on the GH in the site and have a nice `llms.txt` for me to give to my agents.
There's an official Amazon Documentation site that's linked. There's also an `AGENTS.md` file in the repository.

Sure they are, but they could have polished their product and showed some love by configuring the repo details and put the website there. Did you look at the blog post as well? Does it look like a product that some team there loved and will care for?  Or the output of some exercise for some enterprise content?This post https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent... doesn't set the right tone for me at all and it has nothing to do with agents and everything to do with the lens of looking at this as a science experiment instead of a real enterprise tool.

> they could have polished their product and showed some love by configuring the repo details and put the website thereThis feels like such a weird nit-pick when AWS is criticized for not moving quickly enough. Why should I care if there's a link in the side bar, when there's plenty of links in the `README`? If anything, I'm happy that there's alternatives to Localstack that are supported by AWS themselves that I can begin incorporating. They have a well written `README` that I can start working with and a User Guide to get me started. What else could I want?
> Did you look at the blog post as well?
I did.
> Does it look like a product that some team there loved and will care for? Or the output of some exercise for some enterprise content?
Do you even have the grounds to cast judgement like this when you admittedly didn't even look hard enough?

I looked, but you're mistaking my critique here: I value polish.This lacks polish.
Small details like getting your GH repo set up for a public audience.  Lacking.  Compatibility and support matrix clearly advertised?  None.
If this public facing artifact exhibits a lack of care and love, what does it say about the code?  I am all for vibe coding and agent software factories, but then the humans should show some love with all of that extra time saved.

You might want to reconsider how you present the critique then, because that's not how your root comment came across or any of your subsequent messages, especially when engaging with (presumably) actual AWS employees in this thread replying to you.

Look at AWS Copilot CLI https://aws.github.io/copilot-cli/docs/concepts/environments... and the repo https://github.com/aws/copilot-cli/.Look at Floci (I have no affiliation) https://floci.io/ the blog https://floci.io/chronicle/ and the labs https://floci.io/labs/
Do you agree that there's a polish here that shows a team's pride in that work that is clearly missing in this work?
    > ...especially when engaging with (presumably) actual AWS employees in this thread replying to you What even is this statement?  Are AWS employees our benefactors?  Wow.  I do not care if their feelings are hurt because this "product" clearly shows a lack of polish and love.

> Do you agree that there's a polish here that shows a team's pride in that work that is clearly missing in this work?No and I think the inverse is also possible and if anything more likely. You can make a website look really pretty, really easily and have the product still suck. This is "product as a slide" in a new age where making visual eye candy with AI has never been easier.
> I do not care if their feelings are hurt because this "product" clearly shows a lack of polish and love.
The point isn't about hurting feelings. The point is about providing critque and feedback based in reality, not based on "vibes." You're trying to gatekeep people releasing software because you dont like the way they're launching it lol.

Clearly according to whom? You?

If your complaint is about polish, you’re a very poor writer. It should not have taken this many replies to get that point out. But regardless of your communications skills, I disagree - this product looks fine for something released at this stage.

Disclosure: I work for Amazon. I'm not directly involved in building this product, but I'm familiar with the product and its development.The product documentation is here: https://docs.aws.amazon.com/emulator/latest/userguide/what-i...
While the GitHub project is young, the internal effort to build this has been going for quite some time now.

AWS isn’t Google. They tend to maintain everything they put out and they don’t put out things randomly as a result.

Not really. I was trying to use their own Q AI to help me get something set up and it was constantly wrong about what screens to go to, what was on the screens etc... If their own AI doesn't understand AWS, I don't have confident this will either.

It's in their official docs, so probably not just someone's side project: https://docs.aws.amazon.com/emulator/

From the security page [0]> Don’t use the emulator to test the following:
> - IAM policies and permissions boundaries
> - Resource-based policies, such as bucket policies
> - AWS KMS key policies
> - Access across AWS accounts or across AWS Regions
> - Any other security control
> Some services in the emulator evaluate IAM policies for IAM users and roles that you create in the emulator, but not the same way as AWS. The emulator never denies a request signed with its own key. It doesn’t check AWS KMS key policies or Amazon S3 bucket policies. It also doesn’t support calls across accounts or Regions. So a request that AWS denies might succeed in the emulator. A request that AWS allows might fail.
This is a shame because I'd love for the official AWS product to be better than e.g. ministack and localstack on this, which will go some of the distance. I think because the agents were only building on the public API surface, it's hard to build this part. But they should've tried and let the agents read whatever policy engines AWS has. Or maybe it's a way to prevent someone from trivially running aws-emulator as AWSaaS?
[0] https://docs.aws.amazon.com/emulator/latest/userguide/securi...

I suppose it would have been extremely complex to replicate all of that. Maybe they thought it’s out of the scope to emulate all security patterns locally, they just wanted to focus into providing a native alternative to let users do integration tests.

The current IAM engine and language “balsa”, is its own thing. Its vended as a library with large “there be dragons” disclaimers if you even think about going outside the public interfaces. There are also big opaque interactions between different components like STS, KMS, service principals, service-specific resource policy evaluations, etc. I doubt that can be reasonably open sourced or exposed.There was an attempt at a public implementation of the “next gen” AWS IAM language/engine with “cedar.” However I think that got sidetracked as an authz product and didnt have any real penetration with AWS IAM.

I've implemented the AWS IAM engine and all policy types, conditions, etc in here if you want to try it out. It's the most thorough in terms of edge case coverage I'm aware of and I'm constantly adding enhancements and closing edge cases.https://github.com/act-security-labs/iam-lens
It uses https://github.com/act-security-labs/iam-collect to get all the policies which includes example terraform to gather all the data at scale.

I shudder at the thought that local emulation is somehow supposed to handle IAM conditions like source VPC endpoints, EKS Pod Identity, chained roles originating from web identity providers...IAM itself is free. Most IAM conditions involve resources which are free (e.g. VPC gateway endpoints, web identity providers) or which are free additions on top of a cluster you have for other purposes (e.g. EKS Pod Identity). Presumably you already have an AWS account. What value does an emulator give here?

Yep, it's a complicated beast so I'd love to be able to mess around with it out locally! I don't mind using an AWS account for a shared staging environment in the CI pipeline, but trying to figure out policies and roles during development, it can get a bit messy coordinating and handling the lifecycle of resources in a team's testing account (maybe this is easier if you get your own account?). And accounts aren't free when they require GuardDuty etc, unfortunately.

Tried it out, this does not seem to work well. A codebase that runs fine on MiniStack could not be emulated with this official AWS emulator.Specifically it does not support certain SFN fields (like `Assign`) and Lambda Python code was not fully supported, so SFNs and Lambdas did not work and the test had to stop there.

I feel like we don't talk enough about the massive problem of creating local test environments for AWS deployments.An actual AWS supported env that you can run on your local machine would be super useful, even if it just had a subset comprising the most popular services.

Say whatever but without AI and agents, no one in AWS would have thought of building this given the huge amount of services they have. Humanly, possible but very very costly. Not saying has not happened before but fakecloud and localstack etc? That moat is gone.I am shocked TBH that this is the new normal. Agents writing code in one of the most difficult to use languages. And ugly as well TBH, it pokes into your eyes. Subjective I know but it is a horrible language for humans.

Rust is beautiful! The way all the stdlib traits slot into each other satisfies a very particular itch

Like I said - subjective. Crates, modularity, tooling? Nothing comes close to Rust. Period.

You serious? Visually it is one of the most ugliest languages that I know of.

Maybe just behind brainfuck.

Ugly syntax, (mostly) beautiful semantics (at least compared to other mainstream languages). Syntax only makes something cosmetically beautiful.

We are talking about a company with ~3T market cap, right?

Exactly. Amazon is worth 3T because they're really good at cutting cost.

That's for paying execs and buying politicians, not paying workers.

yeah for all the faults with 'a.i' certain things have just become possible because of it.

As a human, beep boop, I find Rust a beautiful language.

> Agents writing code in one of the most difficult to use languagesArguably, languages with strong static guarantees are exceptionally effective for LLMs since they're much quicker to provide feedback to the LLM than a dynamically typed language (which only fails once you actually run it - often several times to find the actual problem). You also get very well-designed build error messages rather than having to parse unstructured stderr output, etc etc.

Yes absolutely - that's objectively true. That's why Typescript, Go and Rust are some of the best languages with LLMs because feedback loop is precise and fast to verify the generated output.

C# is also excellent for LLM generation.

Fellow Amazonian here. Want to say that I’m grateful you built this and it has tremendous value if pulled off well and properly maintained.Agentic development is all about closing off a system as much possible, then mocking up or simulating any inputs or dependencies that cannot be closed off. At that point, you let Claude crawl over the system and do its thing.
This inevitably runs into problems with infrastructure and any tools that help mock up those interfaces will be tremendously valuable. Thank you!

AWS already models all their services with Smithy, the specification language they created. Their API clients are all generated from Smithy, and the emulator seems to have been built using the Smithy specs and comprehensive integration testing against the real APIs. Using the spec ensures they hit every variant and optional field of every endpoint, unlike Floci and Ministack that only implement the more commonly used ones.https://github.com/aws/api-models-aws
https://github.com/smithy-lang/smithy

If I understand this correctly, it means I can point my entire CDK project to the emulator and test a `cdk deploy`?I'm curious just how realistic the "internal" behaviour is emulated.  It's been a while (since I got my stack working and I just don't like touching it now...), but I recall it being a real pain that sometimes odd, sometimes inconsistent things happened with setup and teardown (even through Terraform), which led to long timeouts if you did things in the wrong (but seemingly valid) order.

> I'm curious just how realistic the "internal" behaviour is emulated.It seems like some reasonable shortcuts are taken, like services reading from each other's states directly instead of using APIs [0]. But then it will go so far as to run an in-process NodeJS emulator for lambda functions, and give it a shim so the code it runs can call other emulated AWS services using the main router [1].
[0] https://app.ilograph.com/demo.ilograph.AWS%2520Emulator/Serv... ph.com/demo.ilograph.AWS%2520Emulator/Invoke%2520Lambda%2520Function" target="_blank" rel="nofollow noopener noreferrer">https://app.ilograph.com/demo.ilograph.AWS%2520Emulator/Invo...

You could try but it likely wouldn't be reliable. AWS services have a lot of undocumented business logic that fails only when you trigger the code path. Like trying to create a resource with an attribute with too many characters, or the wrong character, etc. Doesn't fail until you run that call with that specific value. This emulator doesn't contain each service's full business logic, so you won't see the error until you try the real thing.

AFAICT there isn't a quick way to reset state other than restarting the process - in other words it probably isn't a drop in replacement for https://github.com/getmoto/moto for running tons of tests where the state of the mocked AWS system needs to be reset after each test. Hopefully they will implement a quick reset functionality; multiple accounts and full org APIs emulation would be nice too.

I’m curious how you would want to leverage the orgs API or multiple accounts? What’s the use case you are envisioning?

I'm not them but I added AWS Organizations support to moto because we needed to test all of the child account enumeration APIs. If I would have had more time/energy I would have continued my tilting at windmills to have it honor the actual $(aws sts assume-role) keys, too, since hopping between accounts in the org via the injected IAM Role was also very critical to the product at the timeI got a lot of enjoyment out of https://awsteele.com/blog/2020/09/26/aws-access-key-format.h... at the time, too

Related to this post: https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent...

> We’ve had our agents build many versions of this emulator as we’ve refined the building machine.I'm curious how many versions they made and the token spend on each one. There are a lot of failure modes to projects like these (e.g. gas town endlessly developing itself). Is this more of a sly marketing stunt or a real indication that this methodology is practical and economical?
FYI I checked out the repo. `du --apparent-size -h` output for some dirs:
    2.2G . -do-not-work -now-work /tests/ directories. 357 MiB of rust code outside of /tests/ directories. 117 MiB of json. 1 MiB of toml.

> At least 100 GB of free disk for target/. The workspace has one crate per AWS service, so a debug build of everything is large, and it grows as services are added.100GB !??!?!

What makes this any different than fakecloud?https://github.com/faiscadev/fakecloud
I had a good time using its SDK inside my integration tests. I'll give a couple months before even moving to this because it's weird how similar both projects look like.
EDIT: After checking AWS's project I'd say stay away from it, looks heavily vibe slopped.

claude is the second-most frequent author in that fakecloud repo, what makes you say that's not vibeslopped either? This is 100% the perfect usecase of using a swarm of agents. It's a bounded, and easily-verifiable with property testing/mitm proxying, task. If you think in November 2026, agentic engineering is equivalent to vibe coding, you need to update your priors

at least in fakecloud's case, there's still humans being assisted by LLMs.one can also argue that offering SKDs for python / typescript / golang makes the project superior still. So you are not stuck with Rust-only projects.

every codebase has ai code. get over it. humans can be sloppy coders as well.

This will make it even easier for competitors to reliably clone AWS services, which reveals that cloud is fully commoditized at this point, and advantages come down to market power (buying servers/bandwidth at scale, building data centers at scale, etc).

This is my first thought when I saw this as well.

I don’t think AWS is worried about that. If the small cloud provider competitor standardizes on their API, they’re already winning. It will be easier for you to migrate to AWS once you hit the ceiling of the competitor’s scale. That’s something you can’t copy out of the box (and the true AWS value proposition imo).

I think you massively underestimate how big AWS's moat is, and how hard it is for newcomers to effectively compete with them. AWS's ever-growing feature list is impressive, sure, but what customers are actually paying for is good customer service, high reliability, and most importantly, trust that AWS will be around for decades to come and that all infra issues become AWS's problem rather than their own.

Any serious competitor would have already invested the trivial amount of money required to gain full access to AWS to probe and test all their services.

The title for this story should be "aws-emulator, from AWS".

Why?

Because the rules say not to editorialize post titles

The post title is the name of the tool. It's not like a blog post where we can stick to the same copy, one-for-one.

Yes, even "from AWS" is editorializing, and as you can see, even that got cut.

I guess I'll go literal:"expressing a personal opinion, bias, or subjective viewpoint in a context—such as a news report—that is supposed to be strictly factual and objective."
How does the title do any of the above that makes it editorializing?

The original title included “finally”, which adds a bunch of connotation from the submitter.

This simulates API responses, like a mocking mechanism, which is enough for some testing. But if you call RunInstances, the corresponding code of the launched instance doesn't actually run. So if you have orchestration code you want to test, that depends on actually running the instances you launch, this won't test it.Spinifex (https://github.com/mulgadc/spinifex/) seems more promising than this, because its RunInstances actually launches VMs.

I remember asking this to one of the evangelists when AWS first came out, how do I run this locally. This was during the times where we actually tried to get all the .NET and C/C++ docs locally.Now doing the math I feel old.

There was an offline help system in Visual Studio Community 2012 that would cheerfully download all the help files as a pseudo-.zip file, and for sure included both .NET and C++, along with SQL Server and it's my _recollection_ it included Office's OpenXML documentation, too

I'm wondering how much of this was vibecoded

Likely no human ever read the code

Excited to see this develop and be a free replacement to localstack / similar providers.

Localstack is almost entirely free. I’ve used it at our company for years without paying.

Localstack is no longer free and if you’re using it commercially you need to pay for a license. The free plan explicitly states that it is non commercial.https://blog.localstack.cloud/2026-upcoming-pricing-changes/

Except that https://github.com/faiscadev/fakecloud has been a thing for a long time and it's AGPLv3.

All those emulators are usually bad even if it's official,  full of shortcuts and corner cases, just connect to the real service.

im mostly on cloudflare and wrangler dev/miniflare already gives you local workers, d1, r2 etc, but its hand built. the “agents build it and verify against the real service” approach seems like the actual new thing here. wonder if cf does something similar

How do you know its handbuilt?

This is what I've been trying to do for over a decade - you can go even further with tee-testing by making a copy of the live traffic you run in a sandbox environment and match responses against. Obviously you can't do some things in the sandbox, email and payments high on that list, but e.g. payment gateway responses can be "borrowed" from production.Once your new version has no disagreements, it's a really clean swap. I am working towards developing this way and I think, if taken to extremes and carefully, it can remove the review requirement most of the time.

Do I need to get certified to use it?

> How AWS Emulator keeps improving> AI agents keep the emulator up to date with AWS.
Is pretty interesting! No more detail than that tease though.
https://docs.aws.amazon.com/emulator/latest/userguide/what-i...

Thanks to Fable, I’d imagine :)I’ve been having it build local mock APIs for any service that exposes its OpenAPI spec. Works like a charm.

Looks like this was ~100% generated with Claude within the past month. Interestingly it still has a lot of occurrences of words that Opus used way too much pre 5.5, so maybe they're not using the latest models.https://github.com/search?q=repo%3Aaws%2Faws-emulator+load-b...
https://github.com/search?q=repo%3Aaws%2Faws-emulator+%2Fno+...
https://github.com/search?q=repo%3Aaws%2Faws-emulator+golden...

Seems like a great fit for LLM - extensive documentation, plus a live system it can probe against freely to match the behavior.

I mean, if they're using it internally then there's probably a TON of context you can feed these things to converge on approximately-correct solutions. Certainly it sounds like it can be a much better alternative to Localstack/Floci and friends.

29,000 commits in a month is crazy

This is cool, looks like AWS heard all the buzz around emulators like Floci, Ministack, Fakecloud etc. Wonder how this will fit in with proper infra tools like Spinifex.

Wonder if this could be considered a replacement for Ministack which itself was a vibe-code replacement of Localstack?

looks like ministack made an announcment

https://ministack.org/blog/aws-emulator

Hey, I'm one of the MiniStack maintainers. We'll definitely keep maintaining and running MiniStack. We're already well established, with many companies using it, including NVIDIA, NASA, Block, and others.Until the AWS emulator can match all our current capabilities, such as multi-account, multi-region, IAM, running IaC, etc., we'll still be around
One of our core principles has always been to focus on supporting only the most commonly used services

Thank the maker!! I was not having a good time with LocalStack, only an average time. Definitely have to try this out. I need the environment to survive a reboot.

i once saw someone suggest simulation, with a formal model. https://docs.google.com/document/d/154XE2Wx3Ojp7weqaHyrqN9U3...

How did you choose CC0 for the open source license vs relatively more common MIT/BSD/Apache licenses?

The README.md states you need 100GB free disk space to build, and they do not provide binary releases. I hope that changes soon!

Wouldn't be better using agents for simplifying the mess some services like iam or cognito are?

Regarding this distributed lock service ALF:Is AWS offering such a lock service for its costumers ? class="pb-1">
Alf is internal only.

looking at the project history it looks new, if so why did it take AWS so long to put out something like this?

This is no doubt made possible by an agentic coding loop. If you have the right checks in place, it can be easy to emulate existing software.I was able to create a TV emulator at my work with a mostly independent agentic loop, because we have a lot of tests to examine a smart TVs APIs. The agents mostly just need to make the tests pass.

For me, what is interesting in this project is it's git history.

Repo has 29,684 Commits!Code frequency pages shows:
"There are too many commits to generate this graph."
https://github.com/aws/aws-emulator/graphs/code-frequency

First commit two weeks ago. Insane number of commits, even for AI agents. They must be using large fleet of agents.

" the engineer’s job is to give them room to work on their own and to build the specs, tests, and merge gates that decide when that work is correct."I mean that's a job, but in many orgs it's been done by (cheaper) non-engineers (business analysts, QA professionals) for decades. So what does an engineer do?

> for decadesWe haven’t. QA has been part of the process but only one stage of the process mentioned above. How do cheaper non engineers decide if you’ve designed and implemented your query planner, payments gateway, auth, caching strategy, or other similar features correctly?
P.s I don’t doubt that incompetent orgs would do this incorrectly but it’s not sensible to take that as norm.

That's just implementation detail - no engineer is going to be checking the agent's code for all this.

It seems accountability is dead. No wonder it's impossible to get a job or hire for one. Once you're inside some of them, you must be nigh invincible.

Easy to have this attitude when it’s other people’s time and money.

Indeed. The purpose of AI is to enable shareholders to reduce headcount, including (especially) engineering.

Sure, this’s their wet dream and selling dreams and wishes is nothing new. But how’s that working out? https://news.ycombinator.com/item?id=50463899

Does this have pricing data? So you can see how much deployed resources cost?

They wouldn't include it otherwise the binary would be comically large since (as one might guess) there are a lot of knobs involved in pricing AWS things. Just downloading it takes several minutes, served from S3https://github.com/opencost/opencost/blob/v2.5.3/pkg/cloud/a... is the source URL, and while I haven't been in the opencost ecosystem for a while, I'd guess there's a non-zero chance you could legitimately just ask it to price your aws-emulator resources. I am pretty sure there is a terraform/opentofu integration, too, although I don't this second know if it is within opencost or is a separate project

Oh fuck yeah. I was really annoyed by companies wanting you to pay just to use a simple offline emulator which doesn’t cost them anything.

Official post https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent... (https://news.ycombinator.com/item?id=50456319)

Will it be maintained? Or was it more of a toy-project for its large scale agentic blogpost? [0][0] https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent...

it's going to be maintained, official product

~30K commits in 3w; quality software for sure. Is someone trying to get promotion by tokenmaxxing? Ironic or unlucky coincidence or competitor(s) misdirection, that, only 2w ago, Amazon published memo discouraging AI abuse?

That’s cute. I wrote an AWS emulator 10 years ago. A few days, zero tokens, and it actually worked and it didn’t “bleed” requests. It alerted the developers

RIP LocalStack… can’t say I’d be unhappy to see it go though.

> AWS Emulator is configured to collect and report usage data to AWS, to gain insight into how AWS Emulator is used. Telemetry is on by default.They can't help themselves, can they?
I'll stick with Floci and Testcontainers.

> its “things-that-do-not-work” folder holds the issues describing behaviors the agents found that do not yet match real AWS.Claudeslop snuck in at the very end

~6,500 issues that are completely unsorted, btw.(Compared to 12,700 entries in the `things-that-now-work`. I'm not sure if that is a list of bugs found that were then fixed, or if the total list of ~20k things is meant to be the list of features they intend to support.)

The entire AWS emulator was written by agents and will be maintained by agents.

> AWS Emulator is a local emulator of the AWS APIs. You use it to test your software without calling AWS, on your own machine, on a development server, or in continuous integration (CI).Underrated README intro. Gets straight to the point of what it is, and why I should use it. I'm guessing an AI didn't write it.

That’s cute. I wrote an emulator single about 5 years ago. It was about 1000 lines and didn’t take $100k in resources

It's funny to read AI-generated documentation that is the result of a prompt instructing the LLM to be as terse and straightforward as reasonably possible. The agent was probably told to conform to ASD-STE100.It's better than a lot of AI-generated documentation, but it also comes across as a gruff LLM that it is annoyed that it has to write the documentation at all.

I spent a good 10 mins clicking in circles trying to find out which services are supported, surely one of the most critical pieces of information anybody would probably want to know.  I gave up.

I know one day it will be revealed and I'll be proved right, that AI was built just to understand how the heck you get anything done in AWS.

Seems like the bunch of AI induced failures they had "paid off" in getting this done

Mh, no transfer family service... I wonder what else is missing..

29000 commits and no contributors

ok who's gonna build the GUI / web console on top of it?

For what? Use the APIs.

I could see this being useful. Just let Console pick the localhost:xxxx endpoints for everything, boom, my "own" fake AWS.

I was reminded of https://github.com/localstack/local-surf but two things materialized out of trying it out against my local aws-emulator build: AWS Console uses a proxy endpoint just for their console, and is not implemented 100% in terms of "public" AWS api endpoints; and the other is that aws-emulator (as of v1.0.322 anyway) does not expose CORS headers which is fatal to trying to have the extension contact localhostSo, it's possible that some things would work after patching aws-emulator to cough up CORS headers, but I don't know what the state of affairs is for any reverse engineering of their console proxy endpoint. Likely it's available in localstack somewhere, given who made the extension, but I didn't go digging

Can it emulate billing too, i.e. "rand().powf(rand()) % downtime"?

Headlines say written by agents, no humans.No thanks.

This looks great, I'm looking forward to using it!That said, I don't like using Docker for things, and I run macOS on my desktop. Here's a patch that gets it all building on macOS [1] - though there's no good way to upstream it!
[1]: https://github.com/jen20/aws-emulator/tree/jen20/macos-build

Personally, i've done away with all of these managed services and just run everything on NixOS.Cloud provider neutral. Tear it up and tear it down with 100% reproducibility.
If I want to test it locally, I can boot it all up in a disposable VM.

I would for sure read your nix implementation of an auto-scaling group, because I'd enjoy seeing how nix routes traffic to those new instances from your nix network load balancer

annoying that it took AI happening for AWS to finally deliver on this though I'm glad they didironically localstack is solid enough to probably not need this for most things

I guess they didn't decide this was worth it till they needed it to train an LLM, huh? Not like everyone (inside and outside of AWS) has needed such a test harness for years...

After waiting for years for this kind of thing I ended up working around the issue by: using the real service. With Claude's help I have many projects now that test against live hosting providers using accounts maintained exclusively for testing. It ends up costing $50 or so a month in fees but well worthwhile for the assurance things really work.

A mere 20 years too late. Now it’s faster to have AI mock your APIs for you. AI has been a boon for test coverage.

Which is why they used AI to mock these APIs for you... too? I'd expect Amazon to feed it a lot of internal information so it has more to work with than anything someone else can cook up.https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent...

it takes more time for my AI to learn their "emulator" . And I end up with far fewer dependencies on my own.I've been prompting the agents to build everything using stdlib

I think having an interface with your AWS implementation and one for test mocks has always been great advice. With this though, it helps enable better integration testing too. I consider this a testing compliment, but if I had to choose one these days, integration tests are cheaper and better hang for your buck than ever.I'll continue to choose both though, depending on the thing being tested.

If this does not kill you ec2 instances randomly its not emulating shit lol

Finally!

No idea why there's so much of this lately, but there are way too many editorialized submission titles hitting the front page recently.  Please stop doing this.<https://news.ycombinator.com/newsguidelines.html>

Almost every large thread has upvoted comments that violate the comment guidelines, now, too. In both cases, not enough people flagging them, I guess.

Just a little bit more to keep you hooked. You should do your best to stay away from these parasites. Especially if they don't respect your country and your people by not paying the right amount of tax.

Reply on news.ycombinator.com