Running Python on AWS Lambda

The idea of “serverless” fascinates me since I first heard it. Write some code, deploy and voila, your code is globally available. I awaited a chance for get my feet wet and last week I got. In Artistanbul we were toying with the idea to create a Facebook Messenger chatbot for one of our clients. Chatbots are perfect for going serverless, so I volunteered for creating a prototype.

This post is not a tutorial for creating a Facebook Messenger chatbot. I’m writing this just for logging purposes, So I can come back in the future and restart my serverless journey wherever I left.

Lambda looks for handler function to execute your code. Create a handler function and deploy it for testing.

def handler(event, context):
    return {
        'message': f'Hello {event["name"]}'
    }

For deployment you need to create a zip file containing your dependencies and code. For learning purposes I did deployment manually, but you should really checkout Zappa.

$ zip lambda.zip lambda.py

Create the execution role by following the steps described here. Copy role ARN to anywhere accessible.

Get root’s access key id and secret key from IAM Management Console. Note that using root user’s access keys is against Amazon’s recommendation and promise yourself that you will not do this any serious project.

Add security credentials. This will create a directory named .aws and two files: config and credentials.

$ aws configure
AWS Access Key ID [None]: ACCESS_KEY_ID
AWS Secret Access Key [None]: SECRET_ACCESS_KEY
Default region name [None]: eu-central-1
Default output format [None]: json

Create the function by:

$ aws lambda create-function \
    --region eu-central-1 \
    --function-name lambda \
    --zip-file fileb://lambda.zip \
    --role your-role-arn \
    --handler lambda.handler \
    --runtime python3.6 \
    --profile default \
    --timeout 10 \
    --memory-size 1024

To invoke the function create an event template…

{
    "name": "Ege"
}

and invoke from cli:

$ aws lambda invoke \
    --invocation-type RequestResponse \
    --function-name lambda \
    --payload file://test.json \
    output
{
    "StatusCode": 200
}

Note that there are two invocation types of lambda functions: Event (asynchronous execution) and RequestResponse (synchronous execution). If you use Event invocation type the return value of handler will be discarded.

$ cat output
{"message": "Hello Ege"}