AWS emulator

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/

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...

What this means:

If you have a product that has APIs and can be verified, anyone can copy the APIs and the features. By the way, you absolutely want to offer APIs so your product can be used by agents.

This means you need to compete on aspects other than features.

Just because you can emulate all the APIs doesn't mean you can build AWS.

Availability, reputation, performance, domain expertise, price: all of these become critical in a world where features can be copied.

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.

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.

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.

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.

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.

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

> 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.

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).

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

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.

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

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

I'm wondering how much of this was vibecoded

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

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...

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

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.

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 ? Multi regional?

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.

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

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

" 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?

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

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...

~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?

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.

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

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.

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

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.

> 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.

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.

> 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

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?

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.

annoying that it took AI happening for AWS to finally deliver on this though I'm glad they did

ironically 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.

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

Finally!

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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>

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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.

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