Deploying AWS Lambda function using GitLab CI/CD

GitLab allows users to easily deploy AWS Lambda functions and create rich serverless applications.

GitLab supports deployment of functions to AWS Lambda using a combination of:

We have prepared an example with a step-by-step guide to create a simple function and deploy it on AWS.

Additionally, in the How To section, you can read about different use cases, like:

  • Running a function locally.
  • Working with secrets.
  • Setting up CORS.

Alternatively, you can quickly create a new project with a template. The Serverless Framework/JS template already includes all parts described below.

Example

In the following example, you will:

  1. Create a basic AWS Lambda Node.js function.
  2. Link the function to an API Gateway GET endpoint.

Steps

The example consists of the following steps:

  1. Creating a Lambda handler function
  2. Creating a serverless.yml file
  3. Crafting the .gitlab-ci.yml file
  4. Setting up your AWS credentials with your GitLab account
  5. Deploying your function
  6. Testing the deployed function

Lets take it step by step.

Creating a Lambda handler function

Your Lambda function will be the primary handler of requests. In this case we will create a very simple Node.js hello function:

'use strict';

module.exports.hello = async event => {
  return {
    statusCode: 200,
    body: JSON.stringify(
      {
        message: 'Your function executed successfully!'
      },
      null,
      2
    ),
  };
};

Place this code in the file src/handler.js.

src is the standard location for serverless functions, but is customizable should you desire that.

In our case, module.exports.hello defines the hello handler that will be referenced later in the serverless.yml

You can learn more about the AWS Lambda Node.js function handler and all its various options here: https://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-handler.html

Creating a serverless.yml file

In the root of your project, create a serverless.yml file that will contain configuration specifics for the Serverless Framework.

Put the following code in the file:

service: gitlab-example
provider:
  name: aws
  runtime: nodejs10.x

functions:
  hello:
    handler: src/handler.hello
    events:
      - http: GET hello

Our function contains a handler and a event.

The handler definition will provision the Lambda function using the source code located src/handler.hello.

The events declaration will create a AWS API Gateway GET endpoint to receive external requests and hand them over to the Lambda function via a service integration.

You can read more about the available properties and additional configuration possibilities of the Serverless Framework here: https://serverless.com/framework/docs/providers/aws/guide/serverless.yml/

Crafting the .gitlab-ci.yml file

In a .gitlab-ci.yml file in the root of your project, place the following code:

image: node:latest

stages:
  - deploy

production:
  stage: deploy
  before_script:
    - npm config set prefix /usr/local
    - npm install -g serverless
  script:
    - serverless deploy --stage production --verbose
  environment: production

This example code does the following:

  1. Uses the node:latest image for all GitLab CI builds
  2. The deploy stage:
    • Installs the Serverless Framework.
    • Deploys the serverless function to your AWS account using the AWS credentials defined above.

Setting up your AWS credentials with your GitLab account

In order to interact with your AWS account, the GitLab CI/CD pipelines require both AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY to be defined in your GitLab settings under Settings > CI/CD > Variables. For more information please see: https://docs.gitlab.com/ee/ci/variables/README.html#via-the-ui

Note: The AWS credentials you provide must include IAM policies that provision correct access control to AWS Lambda, API Gateway, CloudFormation, and IAM resources.

Deploying your function

git push the changes to your GitLab repository and the GitLab build pipeline will automatically deploy your function.

In your GitLab deploy stage log, there will be output containing your AWS Lambda endpoint URL. The log line will look similar to this:

endpoints:
  GET - https://u768nzby1j.execute-api.us-east-1.amazonaws.com/production/hello

Manually testing your function

Running the following curl command should trigger your function.

Note: Your url should be the one retrieved from the GitLab deploy stage log.
curl https://u768nzby1j.execute-api.us-east-1.amazonaws.com/production/hello

That should output:

{
  "message": "Your function executed successfully!"
}

Hooray! You now have a AWS Lambda function deployed via GitLab CI.

Nice work!

How To

In this section, we show you how to build on the basic example to:

  • Run the function locally.
  • Set up secret variables.
  • Set up CORS.

Running function locally

The serverless-offline plugin allows to run your code locally. To run your code locally:

  1. Add the following to your serverless.yml:

    plugins:
      - serverless-offline
    
  2. Start the service by running the following command:

    serverless offline
    

Running the following curl command should trigger your function.

curl http://localhost:3000/hello

It should output:

{
  "message": "Your function executed successfully!"
}

Secret variables

Secrets are injected into your functions using environment variables.

By defining variables in the provider section of the serverless.yml, you add them to the environment of the deployed function:

provider:
  ...
  environment:
    A_VARIABLE: ${env:A_VARIABLE}

From there, you can reference them in your functions as well. Remember to add A_VARIABLE to your GitLab CI variables under Settings > CI/CD > Variables, and it will get picked up and deployed with your function.

Note: Anyone with access to the AWS environment may be able to see the values of those variables persisted in the lambda definition.

Setting up CORS

If you want to set up a web page that makes calls to your function, like we have done in the template, you need to deal with the Cross-Origin Resource Sharing (CORS).

The quick way to do that is to add the cors: true flag to the HTTP endpoint in your serverless.yml:

functions:
  hello:
    handler: src/handler.hello
    events:
      - http: # Rewrite this part to enable CORS
          path: hello
          method: get
          cors: true # <-- CORS here

You also need to return CORS specific headers in your function response:

'use strict';

module.exports.hello = async event => {
  return {
    statusCode: 200,
    headers: {
      // Uncomment the line below if you need access to cookies or authentication
      // 'Access-Control-Allow-Credentials': true,
      'Access-Control-Allow-Origin': '*'
    },
    body: JSON.stringify(
      {
        message: 'Your function executed successfully!'
      },
      null,
      2
    ),
  };
};

For more information, see the Your CORS and API Gateway survival guide blog post written by the Serverless Framework team.

Writing automated tests

The Serverless Framework example project shows how to use Jest, Axios, and serverless-offline plugin to do automated testing of both local and deployed serverless function.

Examples and template

The example code is available:

You can also use a template (based on the version with tests and secret variables) from within the GitLab UI (see the Serverless Framework/JS template).