AWS distills its cloud into a local emulator that runs on your PC

Hyperscale meets micro-computing by offering APIs to test your apps

AWS has released an emulator that kind-of-almost lets you use its cloud on a PC.

As explained in the GitHub repository for the prosaically named “AWS Emulator,” the tool “is a local program that serves an AWS API endpoint.”

The emulator doesn’t replicate the whole AWS cloud, instead offering its APIs.

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“You use it to test your software without calling AWS, on your own machine, on a development server, or in continuous integration (CI),” the repo explains. Because those tests never touch the AWS cloud, the tool is free to use.

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AWS wrote the emulator in Rust, a choice that senior specialist solutions architect Daniel Abib wrote helps to ensure the tool “stays light on CPU and memory on a laptop.”

The emulator tool doesn’t replicate the entire AWS cloud. Abib said it supports the APIs of AWS services that have an API model in the AWS API models repository on GitHub. The Register found over 1,300 items on that page.

While the tool lets developers test APIs, it doesn’t replicate anywhere near all the features of the Amazonian cloud.

“It doesn’t evaluate IAM [Identity and Access Management] policies the way AWS does, and each emulator acts as a single account, with no cross-account or cross-Region behavior,” Abib wrote, adding “How closely it matches AWS varies by service and feature.”

AWS publishes “fidelity scores” that detail how closely the emulator works on different AWS services. Amazon tries to achieve full fidelity, so the emulator produces the same results as AWS for valid API calls, and the same errors for invalid ones.

Coding agents can also drive the Emulator, an option The Register mentions because AWS advises the easiest way to check if a project will work with the tool is to use the aws-emulator skill for AI coding agents.

“With the skill, your agent finds the AWS operations and resources that your project depends on. It checks them against the fidelity tests and fidelity scores for the emulator. It then tells you which parts of your project you can rely on the emulator for, and which ones might behave differently from AWS,” according to AWS documentation.

AWS has made the emulator available as an RPM or Debian package. Mac and PC users will need to run Docker and an image of the Emulator.

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“You install the emulator, start it, and point your tools at the local endpoint,” Abib instructed. “When AWS Emulator starts, it generates its own credentials, a config file, and a certificate, and writes them to ~/.aws/emulator/9297/. You set environment variables so the AWS SDK talks to your laptop instead of AWS, and your application code stays unchanged.”

“From there, your existing tests, CLI scripts, and coding agents keep working the way they already do. A unit test that creates an Amazon DynamoDB table, writes an item, and reads it back is the same test, and it runs on your machine without a deployment.”

The cloud colossus’s intent appears, as ever, to encourage more use of its cloud – in this case by satisfying developers their code will run well when deployed there, and making it easy for them to test for that. ®