Creating API in AWS Lambda with Flask and Serverless

Introduction to Serverless

If there is a need to quickly deploy an API or have chosen to migrate your development to take advantage of the benefits of AWS Lambda, you may look to make use of Flask and the Serverless framework.

Setting Up Serverless Framework With AWS

Install the serverlessCLI via NPM:

_npm install -g serverless_

To create your first project, run the command below and follow the prompts:

Create a new serverless project serverless

Move into the newly created directory _cd your-service-name_

The _serverless_ command will guide you to:

• create a new project
• configure AWS credentials

Building the Flask App

cd to the directory of your flask app

install flask

pip install Flask
pip freeze > requirements.txt

Let's have a simple hello world Flask app

from flask import Flask, jsonify, request
app = Flask(__name__)
@app.route('/hello', methods=['GET'])
def helloworld():
    if(request.method == 'GET'):
        data = {"data": "Hello World"}
        return jsonify(data)

if __name__ == '__main__':
    app.run(debug=True)

Create a serverless.yml file in your new serverless project. This file specifies what will be deployed to Amazon, such as functions, events, and resources.

service: hello_world #name this whatever you want
provider:
 name: aws
 runtime: python3.9
 region: ap-northeast-1
 memorySize: 128

Let's begin by installing two Serverless plugins. The first step is to teach Lambda about WSGI (the interface Flask/Django uses), and the second is to have Serverless include our Python dependencies in our deployment package.

sls plugin install -n serverless-wsgi
sls plugin install -n serverless-python-requirements

The two lines are necessary, and we can see that Serverless has registered them in our serverless.yml file.

service: hello_world
provider:
 name: aws
 runtime: python3.9
 stage: dev
 region: ap-northeast-1
 memorySize: 128
plugins:
 - serverless-wsgi
 - serverless-python-requirements
custom:
 wsgi:
   app: app.app
   packRequirements: false
functions:
 app:
   handler: wsgi_handler.handler
   events:
     - http: ANY /
     - http: 'ANY {proxy+}'

Deployment

It's as simple as entering one command. Serverless will perform the work if you run _serverless deploy_ in your terminal. Because of the initial preparation, the first deployment will take a little longer, but subsequent ones will be faster.