AWS Built Its Own AWS Emulator So You Can Test Code Without an Account
AWS Finally Built Its Own AWS Emulator
AWS Emulator is a local program that serves AWS API endpoints, letting you run the AWS CLI or any SDK against emulated resources instead of real ones—no AWS account required. It runs in server mode on Linux, Windows, and macOS, or embedded in Rust tests with one isolated instance per test. It's free, but telemetry is on by default and can be disabled via flag, environment variable, config file, or API. AWS says don't use it in production.
AWS Emulator is for building and testing. Don't use it for production workloads or to test security.
- CharlieDigital
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).
- scriptsmith
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...
- wg0
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.
- morelandjs
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!
- Waterluvian
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.
- Thaxll
All those emulators are usually bad even if it's official, full of shortcuts and corner cases, just connect to the real service.
- resters
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).
- super_linear
Related to this post: https://www.aboutamazon.com/news/aws/how-autonomous-ai-agent...