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Building Lambda Functions with Ruby

You can run Ruby code in AWS Lambda. Lambda provides a runtime for Ruby that executes your code to process events. Your code runs in an environment that includes the AWS SDK for Ruby, with credentials from an AWS Identity and Access Management (IAM) role that you manage.

Lambda supports the following Ruby runtimes:

Ruby Runtimes

Name Identifier
Ruby 2.5 ruby2.5

If you don't already have an execution role for function development, create one.

To create an execution role

  1. Open the roles page in the IAM console.

  2. Choose Create role.

  3. Create a role with the following properties.

    • Trusted entity – Lambda.
    • Permissions – AWSLambdaBasicExecutionRole.
    • Role name – lambda-role.

    The AWSLambdaBasicExecutionRole policy has the permissions that the function needs to write logs to CloudWatch Logs.

You can add permissions to the role later, or swap it out for a different role that's specific to a single function.

To create a Ruby function

  1. Open the Lambda console.

  2. Choose Create function.

  3. Configure the following settings:

    • Name – ruby-function.
    • Runtime – Ruby 2.5.
    • Role – Choose an existing role.
    • Existing role – lambda-role.

  4. Choose Create function.

  5. To configure a test event, choose Test.

  6. For Event name, enter test.

  7. Choose Create.

  8. To execute the function, choose Test.

The console creates a Lambda function with a single source file named lambda_function.rb. You can edit this file and add more files in the built-in code editor. Choose Save to save your changes, and choose Test to run your code.

Note
The Lambda console uses AWS Cloud9 to provide an integrated development environment in the browser. You can also use AWS Cloud9 to develop Lambda functions in your own environment. See Working with AWS Lambda Functions in the AWS Cloud9 user guide for more information.

lambda_function.rb defines a function named lambda_handler that takes an event object and a context object. This is the handler function that Lambda calls when the function is invoked. The Ruby function runtime gets invocation events from Lambda and passes them to the handler.

Each time you save your function code, the Lambda console creates a deployment package, which is a ZIP archive that contains your function code. As your function development progresses, you will want to store your function code in source control, add libraries, and automate deployments. Start by creating a deployment package and updating your code at the command line.

The function runtime passes a context object to the handler, in addition to the invocation event. The context object contains additional information about the invocation, the function, and the execution environment. Further information is available from environment variables.

Your Lambda function comes with a CloudWatch Logs log group. The function runtime sends details about each invocation to CloudWatch Logs, and relays any logs that your function outputs during invocation. If your function returns an error, Lambda formats the error and returns it to the invoker.

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