Learn how to set Environment Variables at Runtime in AWS Lambda. Our AWS Support team is here to help you with your questions and concerns.

How to Set Environment Variables at Runtime in AWS Lambda

Did you know that AWS Lambda lets us customize and extend the runtime process using internal extensions?

These internal extensions run as part of the runtime process, providing powerful ways to modify and enhance the behavior of our Lambda functions without creating separate processes.

Furthermore, Lambda offers language-specific environment variables that we can configure to add options and tools to the runtime. These variables enable code to be pre-loaded during function initialization, offering a configuration-only method to set startup properties.

Environment Variables in AWS Lambda

Here’s how to use them:

• JAVA_TOOL_OPTIONS:

  For Java runtimes, this environment variable lets us specify additional command-line variables. It is useful for starting tools and launching native or Java agents using the `agentlib` or `javaagent` options.
• NODE_OPTIONS:

  Available for Node.js runtimes, this variable lets us set Node.js-specific startup options.
• DOTNET_STARTUP_HOOKS:

  For .NET Core 3.1 and above, this variable specifies a path to an assembly (DLL) that Lambda can use during startup.

Using these environment variables we can configure startup properties, as they offer a straightforward way to preload code and tools during the function initialization.

Wrapper Scripts

For more advanced customization, we can create wrapper scripts to modify the runtime startup behavior of our Lambda functions. A wrapper script lets us set configuration parameters that cannot be set through language-specific environment variables.

Furthermore, when we use a wrapper script:

• Lambda starts the runtime using your script, passing the path to the interpreter and all the original arguments for the standard runtime startup.
• Our script can extend or transform the startup behavior. This can include injecting and altering arguments, setting environment variables, or capturing metrics, errors, and other diagnostic information.

To use a wrapper script, we need to set the value of the `AWS_LAMBDA_EXEC_WRAPPER` environment variable to the file system path of an executable binary or script. This tells Lambda to delegate the runtime startup to our script, allowing for significant customization and control over the runtime environment.

Example Use Cases

• Injecting Debugging Tools:

  Use `JAVA_TOOL_OPTIONS` to preload debugging agents in a Java runtime.
• Setting Memory Limits:

  Configure `NODE_OPTIONS` to set memory limits or garbage collection parameters for Node.js.
• Loading Custom Assemblies:

  Use `DOTNET_STARTUP_HOOKS` to load custom .NET assemblies during startup.

With these internal extensions, we can boost the flexibility and functionality of our AWS Lambda functions.

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Conclusion

In brief, our Support Experts demonstrated how to set Environment Variables at Runtime in AWS Lambda.