Writing Clojure Functions for AWS Lambda with Clojure

15.3.1 Writing Clojure Functions for AWS Lambda

In this section, we will explore how to write Clojure functions for AWS Lambda, a powerful serverless computing service that allows you to run code without provisioning or managing servers. AWS Lambda automatically scales your applications by running code in response to triggers such as HTTP requests, changes in data, or system events. Leveraging Clojure’s functional programming capabilities and AWS Lambda’s scalability, you can build robust, efficient, and cost-effective applications.

Setting Up Build Tooling

Before diving into writing Clojure functions for AWS Lambda, it’s essential to set up your development environment with the right tools. Clojure developers typically use Leiningen or Boot for project management. Here, we’ll focus on Leiningen, a popular build automation tool for Clojure.

Creating a New Leiningen Project

To create a new Clojure project using Leiningen, open your terminal and run the following command:

lein new lambda-example

This command generates a new Clojure project named lambda-example with a standard directory structure.

Adding Dependencies

Next, you’ll need to add dependencies to your project.clj file for AWS Lambda integration. Open the project.clj file and add the following dependencies:

(defproject lambda-example "0.1.0-SNAPSHOT"
  :description "A simple Clojure AWS Lambda example"
  :dependencies [[org.clojure/clojure "1.10.3"]
                 [com.amazonaws/aws-lambda-java-core "1.2.1"]
                 [com.amazonaws/aws-lambda-java-events "3.10.0"]]
  :aot :all
  :main lambda-example.core)

• org.clojure/clojure: The core Clojure library.
• com.amazonaws/aws-lambda-java-core: Provides interfaces and classes for AWS Lambda functions.
• com.amazonaws/aws-lambda-java-events: Contains classes for AWS Lambda event types.

AOT Compilation

AWS Lambda requires your Clojure code to be compiled into Java bytecode ahead of time (AOT). This is because Lambda runs on the Java Virtual Machine (JVM) and expects Java classes.

Configuring AOT Compilation

In your project.clj, ensure that AOT compilation is enabled by setting :aot :all. This directive compiles all namespaces in your project to Java bytecode.

:aot :all

This step is crucial as it ensures that your Clojure functions are compiled and packaged correctly for AWS Lambda.

Writing the Lambda Handler Function

The core of your AWS Lambda function is the handler function. This function is the entry point for your Lambda execution and must conform to a specific signature expected by AWS.

Defining the Handler Function

Create a new Clojure source file at src/lambda_example/core.clj and define your handler function:

(ns lambda-example.core
  (:gen-class
   :implements [com.amazonaws.services.lambda.runtime.RequestHandler]))

(defn -handleRequest
  [this input context]
  (let [logger (.getLogger context)]
    (.log logger (str "Received input: " input))
    ;; Process the input and return a response
    {:statusCode 200
     :body (str "Hello, " (:name input) "!")}))

• Namespace Declaration: The :gen-class directive is used to generate a Java class that implements the RequestHandler interface.
• -handleRequest: This is the handler method that AWS Lambda will invoke. It takes three parameters: this, input, and context.
  • this: The instance of the class.
  • input: The input event data.
  • context: Provides runtime information about the Lambda execution environment.

Packaging the Lambda Function

Once your handler function is defined, the next step is to package your Clojure application into a format that AWS Lambda can execute.

Creating the Deployment Package

AWS Lambda requires a deployment package in the form of a ZIP file containing your compiled classes and any dependencies.

1. Compile the Project: Run the following command to compile your Clojure project:

   lein uberjar
   

   This command generates a standalone JAR file containing all your project’s compiled classes and dependencies.

2. Create a ZIP File: Package the JAR file into a ZIP file:

   zip -j lambda-example.zip target/lambda-example-0.1.0-SNAPSHOT-standalone.jar
   

   The -j option strips the directory paths, ensuring that the JAR file is at the root of the ZIP archive.

Deploying to AWS Lambda

With your deployment package ready, you can now deploy your Clojure function to AWS Lambda.

Configuring the Lambda Function

1. Log in to AWS Console: Navigate to the AWS Lambda service.

2. Create a New Lambda Function: Click on “Create function” and choose “Author from scratch.”

3. Function Details:

   • Function name: Enter a name for your Lambda function, e.g., ClojureLambdaExample.
   • Runtime: Select Java 11 as the runtime environment.

4. Upload the Deployment Package: Under “Function code,” choose “Upload from” and select “ZIP file.” Upload the lambda-example.zip file you created earlier.

5. Handler Configuration: Specify the handler using the format namespace.class::method. For our example, it would be:

   lambda_example.core::handleRequest
   

6. Execution Role: Assign an IAM role with necessary permissions for your Lambda function.

7. Create the Function: Click “Create function” to deploy your Clojure Lambda function.

Testing the Lambda Function

After deploying your Lambda function, you can test it directly from the AWS Console.

1. Create a Test Event: Click on “Test” and configure a test event. For example, you can use the following JSON as the input:

   {
     "name": "World"
   }
   

2. Execute the Test: Run the test and check the output. You should see a response similar to:

   {
     "statusCode": 200,
     "body": "Hello, World!"
   }
   

Best Practices and Optimization Tips

• Minimize Cold Start Latency: Cold starts can impact performance. Consider using AWS Lambda provisioned concurrency to reduce latency.
• Optimize Memory and Timeout Settings: Adjust the memory and timeout settings based on your function’s requirements to optimize cost and performance.
• Use Environment Variables: Store configuration data in environment variables to keep your code clean and maintainable.
• Monitor and Log: Utilize AWS CloudWatch for logging and monitoring to gain insights into your Lambda function’s performance and troubleshoot issues.

Common Pitfalls

• Incorrect Handler Specification: Ensure that the handler is specified correctly in the AWS Lambda configuration.
• Missing Dependencies: Verify that all necessary dependencies are included in the deployment package.
• AOT Compilation Errors: Double-check your project.clj for correct AOT settings to avoid runtime errors.

Conclusion

Writing Clojure functions for AWS Lambda enables you to harness the power of functional programming in a serverless environment. By following the steps outlined in this section, you can efficiently develop, package, and deploy Clojure applications on AWS Lambda, leveraging its scalability and cost-effectiveness for your data solutions.

Quiz Time!