04-hello-world-your-first-lambda.md

Hello World - Your First Lambda

This section explains how to deploy and invoke a lambda function. Examples here will use Node JS as the runtime. AWS Lambda supports other runtimes (Python, Ruby, Java, Go lang, .net) also. The document here AWS Lambda Runtimes list them in detail.

(1) Create lambda function

Following command will create a simple nodejs AWS Lambda function handler.

➜  echo "exports.handler =  async (event) => {
  const payload = {
    date: new Date(),
    message: 'Hello Lambda CLI World'
  };
  return JSON.stringify(payload);
};" > helloLambdaCLIWorld.js

Note:

• A handler module should be exported by the lambda js file.
• The handler function is async and takes an event object. The event object contains the request data sent by the caller.
• The function returns a JSON with current timestamp and Hello Lambda CLI World message.

(2) Compress the lambda source file

Packaging the .js file containing the lambda, is done via compression. Following step will compress the lambda js file.

➜  zip -r /tmp/helloLambdaCLIWorld.js.zip helloLambdaCLIWorld.js

(3) Create an IAM Role for Lambda execution

For executing the lambda, it should be associated with a basic IAM Role, AWSLambdaBasicExecutionRole. IAM Roles need policy document. Next sections will create a policy document and an IAM role.

(3.1) Create policy document file

➜  echo '{
   "Version": "2012-10-17",
   "Statement": [
   {
     "Effect": "Allow",
     "Principal": {
        "Service": "lambda.amazonaws.com"
     },
   "Action": "sts:AssumeRole"
   }
 ]
}' > lambdaAssumeRolePolicyDocument.json

(3.2) Create IAM Role attaching the policy document

Here, we create the lambda-cli-role and attach the policy document above.

Note: Create the IAM Role and attaching policy using your default root account. Note the --profile default.

➜  aws iam create-role --role-name lambda-cli-role \
  --assume-role-policy-document file://lambdaAssumeRolePolicyDocument.json --profile default                     

output

{
    "Role": {
        "Path": "/",
        "RoleName": "lambda-cli-role",
        "RoleId": "ABCDEFGHIJABCD9ZYXWV",
        "Arn": "arn:aws:iam::919191919191:role/lambda-cli-role",
        "CreateDate": "2019-01-01T12:00:00Z",
        "AssumeRolePolicyDocument": {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Effect": "Allow",
                    "Principal": {
                        "Service": "lambda.amazonaws.com"
                    },
                    "Action": "sts:AssumeRole"
                }
            ]
        }
    }
}

Arn key in the response is the 'Amazon Resource Name'. The role we created lambda-cli-role can be referred as ARN arn:aws:iam::919191919191:role/lambda-cli-role.

➜  export LAMBDA_ROLE_ARN=arn:aws:iam::919191919191:role/lambda-cli-role 

(3.3) Attach role policies

We also will attach the following permissions. This is to enable the lambdas for integrating with other AWS services, in coming sections.

1. AWSLambdaFullAccess
2. AWSLambdaKinesisExecutionRole

➜  aws iam attach-role-policy --policy-arn arn:aws:iam::aws:policy/AWSLambdaFullAccess \
  --role-name lambda-cli-role --profile default

➜  aws iam attach-role-policy --policy-arn arn:aws:iam::aws:policy/service-role/AWSLambdaKinesisExecutionRole \
  --role-name lambda-cli-role --profile default

(4) Deploy the lambda

The compressed lambda file is deployed using CLI to the region configured in the profile. We will use the compressed lambda file, the role ARN for the IAM created, the lambda-cli-user profile

Note : We will directly upload the lambda function and will not use S3.

➜  export AWS_REGION=us-east-1
➜  export AWS_PROFILE=lambda-cli-user
➜  aws lambda create-function \
       --region "$AWS_REGION" \
       --function-name helloLambdaCLIWorld \
       --handler 'helloLambdaCLIWorld.handler' \
       --runtime nodejs10.x \
       --role "$LAMBDA_ROLE_ARN" \
       --zip-file 'fileb:///tmp/helloLambdaCLIWorld.js.zip' \
       --profile "$AWS_PROFILE"

output

{
    "FunctionName": "helloLambdaCLIWorld",
    "FunctionArn": "arn:aws:lambda:us-east-1:919191919191:function:helloLambdaCLIWorld",
    "Runtime": "nodejs10.x",
    "Role": "arn:aws:iam::919191919191:role/lambda-cli-role",
    "Handler": "helloLambdaCLIWorld.handler",
    "CodeSize": 339,
    "Description": "",
    "Timeout": 3,
    "MemorySize": 128,
    "LastModified": "2019-01-01T12:00:00.370+0000",
    "CodeSha256": "aBcDEeFG1H2IjKlM3nOPQrS4Tuv5W6xYZaB+7CdEf8g=",
    "Version": "$LATEST",
    "TracingConfig": {
        "Mode": "PassThrough"
    },
    "RevisionId": "a123b456-789c-0123-4def-g5hij6k789l0"
}

(5) Invoke the lambda

➜  aws lambda invoke --function-name helloLambdaCLIWorld \
    --log-type Tail \
    --payload '{}' \
    --profile "$AWS_PROFILE" outputfile.txt

➜  cat outputfile.txt

You should see the following output after executing the lambda function.

output

"{\"date\":\"2019-01-01T12:00:00.000Z\",\"message\":\"Hello Lambda CLI World\"}"

🏁 Congrats ! You deployed your first AWS Lambda function and invoked it successfully. 🏁

Next: View Lambda Logs