1. On a short time horizon, not as sure, back of the napkin, it took ~12 dev months (5 months with 2.5 people average on it). However, our cost per 1000 msgs/sec is much lower (like 1/4 the cost of Kinesis) so we fully expect that investment to pay off over time assuming that adoption by the rest of the org continues and we don't find a ton of issues.

1a. You are correct we didn't require geo-replication for existing use cases, however, initially, we saw geo-replication as an easy way to improve DR and we have an internal requirement for a DR zone in another region. Now that we have done the work, we are starting to see multiple places where we can simplify some things with geo-replication, so we think long term the feature will be really valuable

2. We split up auth into two main components: auth of users (where we use Okta) and auth of services. For okta, we just wrote a small webapp that users can log into via OKta and generate credentials. For apps/services, we already had hashicorp in place and wanted to just piggyback of our existing form of identity (IAM roles). Essentially, a user just associates an IAM role with a pulsar role and we generate and drop off credentials into a per-role unique shared location in vault that any IAM role can access (across multiple AWS accounts)

3. Once again, geo-replication wasn't really a hard requirement initially but more of something that we really like now that we have. I think the biggest reason why not postgres is that we have combined message rates (not everything is migrated yet) on the order of 300k msgs/sec across a few dozen services. Pulsar is designed to scale horizontally and also has really great organizational primitives as well as an ecosystem of tools. While I think you could maybe figure that out with some PG solution, having something purpose built really can pay big dividends for when you are trying to make a solution that can easily integrate into a complex ecosystems of many teams and many different apps/use cases