Python Based Lambda Tutorial

If you’ve been following my Medium Blog recently, you’ll know that I’m a huge fan of Serverless and I genuinely believe that it will start to seriously take off in terms of popularity in the years to come.

In this tutorial, we are going to be writing a very simple Python based AWS Lambda function that we’ll then deploy using the serverless.com CLI.

Installing Serverless

In order to install the serverless CLI you can do the following:

$ npm install serverless -g

If you have set up your AWS credentials correctly with an account that has full permissions then you will now be able to deploy Lambda functions that sit behind an API gateway with ease.

Our Function

Create a new directory in which you can add Python files. Within this new directory create a file called simple.py as well as a serverless.yml file.

## directory structure
mydirectory/
- simple.py
- serverless.yml

Open up the simple.py file and create a new function within this called def hello(event, context):. This hello() function will be the main entry point for our AWS Lambda function and when we call the endpoint, this is what will be executed.

Within this hello() function, we want to return the string hello, world back to anyone who calls said lambda function.

def hello(event, context):

    response = {
        "statusCode": 200,
        "body": 'hello, world'
    }

    return response

Deploying Without Serverless

If you wished, you could deploy this without the serverless CLI, you could do so through using either the aws-cli or through the console and either uploading your lambda function as a .zip file or through the inline editor.

Our Serverless.yml File

Within our serverless.yml file we will want to define how we want to expose our lambda function. Let’s step through this line-by-line.

## we define the name our service
service: hello-world

## We pin the version of the serverless cli we want to use
frameworkVersion: ">=1.1.0 <2.0.0"

## we specify which cloud provider we want to deploy to
## as well as the runtime, in this case python3.6
## and the region we wish to deploy to
provider:
  name: aws
  runtime: python3.6
  region: eu-west-1

## We define our list of functions
functions:
  ## our hello function
  hello:
    ## the file name and the function that
    ## makes up our function: simple(.py).hello()
    handler: simple.hello
    ## We define the event we wish to trigger this with
    events:
      ## in this case a simple HTTP GET Request
      ## with CORS enabled
      - http:
          path: hello
          method: get
          cors: true

Deployment

Once we are happy with our function and we have our serverless.yml defined, we can deploy this function by calling serverless deploy within the same directory as our simple.py and serverless.yml file.

When we run this, you should see the following output:

$ serverless deploy
Serverless: Packaging service...
Serverless: Excluding development dependencies...
Serverless: Creating Stack...
Serverless: Checking Stack create progress...
.....
Serverless: Stack create finished...
Serverless: Uploading CloudFormation file to S3...
Serverless: Uploading artifacts...
Serverless: Uploading service .zip file to S3 (225 B)...
Serverless: Validating template...
Serverless: Updating Stack...
Serverless: Checking Stack update progress...
.................................
Serverless: Stack update finished...
Service Information
service: hello-world
stage: dev
region: eu-west-1
stack: hello-world-dev
api keys:
  None
endpoints:
  GET - https://9hqihpd4c2.execute-api.eu-west-1.amazonaws.com/dev/hello
functions:
  hello: hello-world-dev-hello

You should notice the endpoints list has a GET request endpoint that you should be able to navigate to now should you wish. When you open this up in a browser, you should see the words hello, world output to your browser.

Conclusion

Hopefully, you found this tutorial educational! If you require any further assistance then please feel free to let me know in the comments section below!