flask

Flask example

A basic Flask application example. You can build and test it locally as a typical Flask application.

Using AWS Lambda Adapter, You can package this web application into Docker image, push to ECR, and deploy to Lambda, ECS/EKS, or EC2.

The application can be deployed in an AWS account using the Serverless Application Model. The template.yaml file in the root folder contains the application definition.

The top level folder is a typical AWS SAM project. The app directory is a flask application with a Dockerfile.

FROM public.ecr.aws/docker/library/python:3.8.12-slim-buster
COPY --from=public.ecr.aws/awsguru/aws-lambda-adapter:0.8.3 /lambda-adapter /opt/extensions/lambda-adapter
WORKDIR /var/task
COPY app.py requirements.txt ./
RUN python3.8 -m pip install -r requirements.txt
CMD ["gunicorn", "-b=:8080", "-w=1", "app:app"]

Line 2 copies lambda adapter binary into /opt/extensions. This is the only change to run the Flask application on Lambda.

COPY --from=public.ecr.aws/awsguru/aws-lambda-adapter:0.8.3 /lambda-adapter /opt/extensions/lambda-adapter

Pre-requisites

The following tools should be installed and configured.

• AWS CLI
• SAM CLI
• Python
• Docker

Deploy to Lambda

Navigate to the sample's folder and use the SAM CLI to build a container image

$ aws ecr-public get-login-password --region us-east-1 | docker login --username AWS --password-stdin public.ecr.aws
$ sam build

This command compiles the application and prepares a deployment package in the .aws-sam sub-directory.

To deploy the application in your AWS account, you can use the SAM CLI's guided deployment process and follow the instructions on the screen

$ sam deploy --guided

Please take note of the container image name. Once the deployment is completed, the SAM CLI will print out the stack's outputs, including the new application URL. You can use curl or a web browser to make a call to the URL

...
---------------------------------------------------------------------------------------------------------
OutputKey-Description                        OutputValue
---------------------------------------------------------------------------------------------------------
FlaskApi - URL for application            https://xxxxxxxxxx.execute-api.us-west-2.amazonaws.com/
---------------------------------------------------------------------------------------------------------
...

$ curl https://xxxxxxxxxx.execute-api.us-west-2.amazonaws.com/

Run the docker locally

We can run the same docker image locally, so that we know it can be deployed to ECS Fargate and EKS EC2 without code changes.

$ docker run -d -p 8080:8080 {ECR Image}

Use curl to verify the docker container works.

$ curl localhost:8080/