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Comment by mesofile | Hacker News Reader

One thing that I wish I'd known when I first started to use Cost Allocation Tags in AWS as described in the article -- they won't apply to any resources created before the tag was created & activated. Well, you can apply them but they won't return data to your cost reports. For some resources this is not a big deal -- any individual EC2 instance I can respawn pretty easily, or I'm not doing my job right. But there's lots of things in the accounts I administrate that would be far less trivial to re-create, due as much to organizational issues as technical ones. Being able to apply CATs to old resources and start getting cost data back would be a huge improvement for my day-to-day work.

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> Being able to apply CATs to old resources and start getting cost data back would be a huge improvement for my day-to-day work

For what services can't you do this? I recently made a script that iterated over all DynamoDB Tables, Lambdas, SQS, Kinesis Firehose/Analytics/Streams, S3 Buckets, etc. and added a tag to track cost on the individual services.

The only thing I can think of is that you will not have any data before the data you added the tag on.

Yeah - their complaint, albeit ambiguously stated, seemed to be that you couldn't retroactively allocate historical charges to a newly placed tag.

Sorry for the ambiguity -- but no, I mean getting historical cost data retroactive to the resource creation would be great, but I can understand why that's not possible. What I'm saying is that Cost Allocation Tags specifically won't return any cost data for resources that are older than that CAT's activation date. So not only do I not get past costs but I don't get anything going forward. I went on a tagging spree a while back and then spent a bunch of time later down the road trying to figure out why it was getting info for some things and not others.

Is that how it works? It's been a long while since I first set up tags for Cost Explorer, but I'm fairly certain it must have applied to, say, pre-existing EC2 instances and so on or else I never would have had it working...

Is this an EC2 thing? I've definitely added a new tag to a two year old DynamoDB table and started getting data.

For any service -- say EC2:

  - launch instance A  
  - create a new CAT and activate it in the Billing console 
  - apply CAT to instance A 
  - get no cost data back for that instance in Cost Explorer filtering on that CAT 
  - terminate instance A 
  - launch instance B 
  - apply CAT to instance B 
  - get cost data back for that instance in Cost Explorer filtering on that CAT

It was explained to me by AWS support that this is in fact how it works, after I opened a case into why I wasn't getting full data back for some legacy stuff. So for any new account I would say that your tagging scheme should get built first, before infrastructure or anything else.

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