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 our Lambda function we have to set the environment property, when instantiating the function construct.

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 our case the array of availability zones.

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

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 #

• AWS CDK Tutorial for Beginners - Step-by-Step Guide
• How does AWS CDK work
• What is a Token in AWS CDK
• CDK Constructs - Complete Guide
• What is an identifier (id) in AWS CDK
• How to use Context in AWS CDK
• How to use Parameters in AWS CDK