Building resilient serverless applications using chaos engineering

Post Syndicated from Marcia Villalba original

This post is written by Suranjan Choudhury (Head of TME and ITeS SA) and Anil Sharma (Sr PSA, Migration) 

Chaos engineering is the process of stressing an application in testing or production environments by creating disruptive events, such as outages, observing how the system responds, and implementing improvements. Chaos engineering helps you create the real-world conditions needed to uncover hidden issues and performance bottlenecks that are challenging to find in distributed applications.

You can build resilient distributed serverless applications using AWS Lambda and test Lambda functions in real world operating conditions using chaos engineering.  This blog shows an approach to inject chaos in Lambda functions, making no change to the Lambda function code. This blog uses the AWS Fault Injection Simulator (FIS) service to create experiments that inject disruptions for Lambda based serverless applications.

AWS FIS is a managed service that performs fault injection experiments on your AWS workloads. AWS FIS is used to set up and run fault experiments that simulate real-world conditions to discover application issues that are difficult to find otherwise. You can improve application resilience and performance using results from FIS experiments.

The sample code in this blog introduces random faults to existing Lambda functions, like an increase in response times (latency) or random failures. You can observe application behavior under introduced chaos and make improvements to the application.

Approaches to inject chaos in Lambda functions

AWS FIS currently does not support injecting faults in Lambda functions. However, there are two main approaches to inject chaos in Lambda functions: using external libraries or using Lambda layers.

Developers have created libraries to introduce failure conditions to Lambda functions, such as chaos_lambda and failure-Lambda. These libraries allow developers to inject elements of chaos into Python and Node.js Lambda functions. To inject chaos using these libraries, developers must decorate the existing Lambda function’s code. Decorator functions wrap the existing Lambda function, adding chaos at runtime. This approach requires developers to change the existing Lambda functions.

You can also use Lambda layers to inject chaos, requiring no change to the function code, as the fault injection is separated. Since the Lambda layer is deployed separately, you can independently change the element of chaos, like latency in response or failure of the Lambda function. This blog post discusses this approach.

Injecting chaos in Lambda functions using Lambda layers

A Lambda layer is a .zip file archive that contains supplementary code or data. Layers usually contain library dependencies, a custom runtime, or configuration files. This blog creates an FIS experiment that uses Lambda layers to inject disruptions in existing Lambda functions for Java, Node.js, and Python runtimes.

The Lambda layer contains the fault injection code. It is invoked prior to invocation of the Lambda function and injects random latency or errors. Injecting random latency simulates real world unpredictable conditions. The Java, Node.js, and Python chaos injection layers provided are generic and reusable. You can use them to inject chaos in your Lambda functions.

The Chaos Injection Lambda Layers

Java Lambda Layer for Chaos Injection

Java Lambda Layer for Chaos Injection

The chaos injection layer for Java Lambda functions uses the JAVA_TOOL_OPTIONS environment variable. This environment variable allows specifying the initialization of tools, specifically the launching of native or Java programming language agents. The JAVA_TOOL_OPTIONS has a javaagent parameter that points to the chaos injection layer. This layer uses Java’s premain method and the Byte Buddy library for modifying the Lambda function’s Java class during runtime.

When the Lambda function is invoked, the JVM uses the class specified with the javaagent parameter and invokes its premain method before the Lambda function’s handler invocation. The Java premain method injects chaos before Lambda runs.

The FIS experiment adds the layer association and the JAVA_TOOL_OPTIONS environment variable to the Lambda function.

Python and Node.js Lambda Layer for Chaos Injection

Python and Node.js Lambda Layer for Chaos Injection

When injecting chaos in Python and Node.js functions, the Lambda function’s handler is replaced with a function in the respective layers by the FIS aws:ssm:start-automation-execution action. The automation, which is an SSM document, saves the original Lambda function’s handler to in AWS Systems Manager Parameter Store, so that the changes can be rolled back once the experiment is finished.

The layer function contains the logic to inject chaos. At runtime, the layer function is invoked, injecting chaos in the Lambda function. The layer function in turn invokes the Lambda function’s original handler, so that the functionality is fulfilled.

The result in all runtimes (Java, Python, or Node.js), is invocation of the original Lambda function with latency or failure injected. The observed changes are random latency or failure injected by the layer.

Once the experiment is completed, an SSM document is provided. This rolls back the layer’s association to the Lambda function and removes the environment variable, in the case of the Java runtime.

Sample FIS experiments using SSM and Lambda layers

In the sample code provided, Lambda layers are provided for Python, Node.js and Java runtimes along with sample Lambda functions for each runtime.

The sample deploys the Lambda layers and the Lambda functions, FIS experiment template, AWS Identity and Access Management (IAM) roles needed to run the experiment, and the AWS Systems Manger (SSM) Documents. AWS CloudFormation template is provided for deployment.

Step 1: Complete the prerequisites

  • To deploy the sample code, clone the repository locally:
    git clone
  • Complete the prerequisites documented here.

Step 2: Deploy using AWS CloudFormation

The CloudFormation template provided along with this blog deploys sample code. Execute

When this is complete, it returns the StackId that CloudFormation created:

Step 3: Run the chaos injection experiment

By default, the experiment is configured to inject chaos in the Java sample Lambda function. To change it to Python or Node.js Lambda functions, edit the experiment template and configure it to inject chaos using steps from here.

Step 4: Start the experiment

From the FIS Console, choose Start experiment.

 Start experiment

Wait until the experiment state changes to “Completed”.

Step 5: Run your test

At this stage, you can inject chaos into your Lambda function. Run the Lambda functions and observe their behavior.

1. Invoke the Lambda function using the command below:

aws lambda invoke --function-name NodeChaosInjectionExampleFn out --log-type Tail --query 'LogResult' --output text | base64 -d

2. The CLI commands output displays the logs created by the Lambda layers showing latency introduced in this invocation.

In this example, the output shows that the Lambda layer injected 1799ms of random latency to the function.

The experiment injects random latency or failure in the Lambda function. Running the Lambda function again results in a different latency or failure. At this stage, you can test the application, and observe its behavior under conditions that may occur in the real world, like an increase in latency or Lambda function’s failure.

Step 6: Roll back the experiment

To roll back the experiment, run the SSM document for rollback. This rolls back the Lambda function to the state before chaos injection. Run this command:

aws ssm start-automation-execution \
--document-name “InjectLambdaChaos-Rollback” \
--document-version “\$DEFAULT” \
--parameters \
”]}’ \
--region eu-west-2

Cleaning up

To avoid incurring future charges, clean up the resources created by the CloudFormation template by running the following CLI command. Update the stack name to the one you provided when creating the stack.

aws cloudformation delete-stack --stack-name myChaosStack

Using FIS Experiments results

You can use FIS experiment results to validate expected system behavior. An example of expected behavior is: “If application latency increases by 10%, there is less than a 1% increase in sign in failures.” After the experiment is completed, evaluate whether the application resiliency aligns with your business and technical expectations.


This blog explains an approach for testing reliability and resilience in Lambda functions using chaos engineering. This approach allows you to inject chaos in Lambda functions without changing the Lambda function code, with clear segregation of chaos injection and business logic. It provides a way for developers to focus on building business functionality using Lambda functions.

The Lambda layers that inject chaos can be developed and managed separately. This approach uses AWS FIS to run experiments that inject chaos using Lambda layers and test serverless application’s performance and resiliency. Using the insights from the FIS experiment, you can find, fix, or document risks that surface in the application while testing.

For more serverless learning resources, visit Serverless Land.