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AWS Lambda Test Runner

Run your unit tests with Maven or SBT directly on AWS Lambda. For related Jenkins plugin see here.

Project status

Many thanks to everyone who decided to give this solution a try. Some two years after initial release I made a decision to finally discontinue this project. The concept is still great. However, there are some very tangible obstacles preventing widespread adoption. These include:

  • There are certain limits of AWS Lambda functions which will render this solution not feasible for many.
  • There is certain level of complexity involved in initial configuration. It's not a rocket science and there is Terraform automation available, but it still requires certain degree of familiarity with AWS.
  • More organisations talk about cloud than actually use it.
  • Last but not least, development and integration testing of the complete solution is a tad complex.

I wish you best of luck with your cloud journey!

Project history

It all started one day when I was updating my Packer templates for building my Jenkins EC2 slaves. I asked myself: "Hold on, why am I doing this? Isn't running unit tests a perfect use case for AWS Lambda?". I think it is, and this is how it all began - I have started this open source project as an experiment aiming to explore how much AWS Lambda serverless technology can help us test our software.

Project goal

To provide an efficient test runner based on AWS Lambda technology for the Java ecosystem.

Project aspirations

  • Provide support for multiple Git hostings.
  • Provide support for multiple build tools.
  • Provide the runner, not the orchestration. In other words, if your current CI server is Jenkins, AWS Lambda Test Runner may help you reduce your dependency on Jenkins slaves, not on Jenkins master. Of course, you don't have to be using Jenkins to use AWS Lambda Test Runner.


  • Up to 1000 concurrent executions.
  • No maintenance of build agents.
  • You don't pay for what you don't use.

Supported platforms

Git hosting

  • GitHub - HTTPS and SSH
  • BitBucket - HTTPS and SSH
  • GitLab - HTTPS and SSH
  • Other - not verified

Build tools

  • Maven - requires Maven Wrapper
  • SBT - requires core SBT binaries to be included in your repo
  • Gradle - currently not supported due to required disk space
  • Other - not verified

Java version

Java version used to run the tests:

  • OpenJDK 9.0.4
  • OpenJDK 10.0.2 (default)
  • OpenJDK 11.0.2
  • OpenJDK 12.0.1
  • Other - not supported

How it works

AWS Lambda Test Runner will:

  • Install JDK to /tmp on first run, as Java runtime for AWS Lambda doesn't ship with javac.
  • Get SSH key from S3, if Git repository URI is for cloning with SSH.
  • Clone Git repository you passed in your request to /tmp using JGit library.
  • Run shell command which you passed in your request. There are no build tools available on Lambda, so it needs to be included in your repo. See Build tools and Build tool examples for more information.
  • Store build outputs to S3, if requested. Test execution log is always stored to S3.
  • Log events to CloudWatch Logs.

Sample execution log from CloudWatch Logs:


This is the big picture:

How to deploy it

  • You can either start by downloading the JAR from Releases tab, or building it yourself. If you decide to go for the latter, clone the repo and build Java JAR file with: ./mvnw clean package -DskipTests.
  • Deploy it to your AWS account. There is Terraform scripts to speed things up. Before running terraform apply, you will need to:
  • Don't forget to check Required environment variables.
  • If you plan to clone Git repositories over SSH, create private S3 bucket and upload private SSH key as a private S3 object. Bucket name and object key have to match variables s3_bucket_ssh_keys and s3_bucket_object_ssh_key_key defined in tf/

Required environment variables

All Lambda configuration is managed through environment variables. See tf/ for details.

Variables you may want to customize:

  • BUILD_OUTPUTS - S3 bucket for storing build outputs. If you followed How to deploy it it should be already customized.
  • JAVA_VERSION - Java version used to run the tests. Options: 9.0.4, 10.0.2 (default), 11.0.2, 12.0.1.
  • LOG_LEVEL - you can switch between info and debug.
  • M2_CLEANUP - if set to true, MAVEN_USER_HOME will be purged at the beginning of every execution to free up disk space.
  • SBT_CLEANUP - if set to true, SBT_GLOBAL_BASE and SBT_IVY_HOME will be purged at the beginning of every execution to free up disk space.
  • SSH_KEY_BUCKET and SSH_KEY_KEY - your S3 bucket and object key with private SSH key (see SSH access). If you followed How to deploy it, both should be already customized.

No other environment variables are expected to be modified without a good reason.

Usage example

AWS Lambda Test Runner is an AWS Lambda function and can be invoked like other Lambdas. To make it easier for Jenkins users, there is a Jenkins Plugin for AWS Lambda Test Runner which you can use to trigger the execution. If you do not use Jenkins, or prefer to orchestrate the execution yourself, below is a step-by-step guide to executing already deployed AWS Lambda Test Runner using aws cli. It requires all necessary tools to be installed and configured.

Below is sample JSON payload:

cat wiremock-maven-plugin-payload.json 
  "repoUri": "",
  "branch": "master",
  "command": "./mvnw test -Dmaven.repo.local=${MAVEN_USER_HOME}",
  "storeToS3" : ["target/surefire-reports"]

This payload tells AWS Lambda Test Runner which Git repo to clone, which branch to check out, how to run the tests and which build outputs you want to store to S3.

Now we will use this payload to invoke Lambda function:

aws lambda invoke --function-name LambdaTestRunner --region eu-west-2 --cli-read-timeout 0 \
  --payload file://wiremock-maven-plugin-payload.json wiremock-maven-plugin-response.json

It is critical to override the default maximum socket read time with --cli-read-timeout. If we don't do that and our tests take more than 60s to execute, Lambda will automatically trigger a retry with all its consequences. This is not the behaviour we want.

This assumes your Lambda is named LambdaTestRunner and was deployed to eu-west-2. The JSON response will be stored to wiremock-maven-plugin-response.json.

Now you can inspect content of the wiremock-maven-plugin-response.json file:

cat wiremock-maven-plugin-response.json

It should look similar to this one:

  "output": "...",
  "exitCode": 0,
  "s3Prefix": "2018-12-11-13-33-10",
  "requestId": "418eaf5d-fd49-11e8-8fd7-ade5a41cf0d6"

We can now read s3Prefix into S3_PREFIX variable, which we will use in a subsequent command:

S3_PREFIX=$(jq -r ".s3Prefix" wiremock-maven-plugin-response.json)

Now we can fetch from S3 the build outputs. You will need to substitute the S3 bucket I use in the example below ( with your own S3 bucket name - see How to deploy it for details:

aws s3 cp --exclude "*" --include "${S3_PREFIX}*" --recursive \
  s3:// .

At this point we have the build outputs on the local file system. This will include:

  • Test execution log in test-execution.log.
  • ZIP files with the directories we requested to store to S3, in this case target/

They can be now processed in the usual way.

Request parameters

Below is an example of an invokation request with all supported parameters:

  "repoUri": "",
  "branch": "master",
  "command": "./mvnw test -Dtest=SmokeTest -Dmaven.repo.local=${MAVEN_USER_HOME}",
  "storeToS3" : ["target/surefire-reports", "target/surefire-reports"]


  • repoUri: (Required) URI of Git repo to clone. Both HTTPS and SSH clones are supported.
  • command: (Required) Command to run the tests. See Build tool examples for more information.
  • branch: (Optional) Git branch. If not specified, defaults to HEAD.
  • storeToS3: (Optional) list of directories to store to S3. Valid values include: ["target/surefire-reports", "target/failsafe-reports"], ["target/surefire-reports"], [].

Build tool examples

Sample request payload for running Maven tests:

  "command": "./mvnw test -Dmaven.repo.local=${MAVEN_USER_HOME}",

Sample request payload for running SBT tests:

  "command": "./sbt${SBT_GLOBAL_BASE} -Dsbt.ivy.home=${SBT_IVY_HOME} test",

JVM options defined in the above examples are necessary due to locations other than /tmp not being writable on AWS Lambda.

Git repository SSH access

To clone public repos, you should provide HTTPS URL in your request payload. If you intend to clone only public repos, you can ignore remainder of this section.

To clone private repos, you should provide SSH URL in your request payload, as well as configure a few other things:

  • Set SSH_KEY_BUCKET and SSH_KEY_KEY environment variables (see Required environment variables) to point at the SSH key you want to use.
  • The SSH key you use should be compliant with both JGit and the Git hosting you are using. To generate such SSH key, you can use this command: ssh-keygen -m PEM -t rsa -b 4096


Usual AWS Lambda service limits apply. As of November 2018, the key limits you'll be interested in are:

  • Function memory allocation: up to 3008 MB.
  • Function timeout: 900 seconds (15 minutes).
  • /tmp directory storage: 512 MB.

If your tests need more time or memory to run, you won't be able to run them using AWS Lambda Test Runner. Pay special attention to 512 MB directory storage limit - it needs to accommodate unpacked JDK, your repo and local Maven cache in .m2.

I expect AWS to increase these limits in future. They have already increased function memory allocation limit and function timeout in the past. Adding more disk space or adding the ability to mount EFS has also been a common request among the AWS user community.