How to pass Environment Variables to Lambda in AWS CDK

Passing Environment Variables to Lambda Functions in CDK #

In order to pass environment variables to a Lambda function, we have to set the environment property, when instantiating the function construct.

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const myFunction = new NodejsFunction(this, id, {
  // setting environment variables 👇
  environment: {
    region: cdk.Stack.of(this).region,
    availabilityZones: JSON.stringify(cdk.Stack.of(this).availabilityZones),
    myEnvVariable: 'some value',
  },
  runtime: lambda.Runtime.NODEJS_14_X,
  memorySize: 1024,
  timeout: cdk.Duration.seconds(5),
  handler: 'main',
  entry: path.join(__dirname, `/../src/my-function/index.js`),
});

The environment object is a map of key value pairs of type string. This means that we have to call JSON.stringify on any non-string value that we want to pass to the lambda function - in this case the array of availability zones.

In our lambda function code we can access the environment variables by using the process.env object.

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async function main(event) {
  // accessing environment variables 👇
  console.log('region 👉', process.env.region)
  console.log('availabilityZones 👉', process.env.availabilityZones)
  console.log('myEnvVariable 👉', process.env.myEnvVariable)

  return {body: JSON.stringify({message: 'SUCCESS'}), statusCode: 200};
}

module.exports = {main};

The result of the function invocation looks like:

We can also verify that the environment variables have been set by opening the Lambda AWS console and clicking on Configuration:

Summary #

In order to pass environment variables to a Lambda function we have to set the environment property on the function construct to a map of key value pairs of type string.

We are then able to access the environment variables on the process.env object in our lambda function.

Further Reading #

• How to add permissions to Lambda Functions in AWS CDK
• Lambda Function Example in AWS CDK - Complete Guide
• Write TypeScript Lambda functions in AWS CDK - Complete Guide
• Configure Lambda Log Retention in AWS CDK
• Create Lambda Functions in a VPC in AWS CDK
• How to use Lambda Layers in AWS CDK - Complete Guide
• AWS CDK Tutorial for Beginners - Step-by-Step Guide
• How to use Context in AWS CDK
• How to use Parameters in AWS CDK