Serverless Framework Python Flask API on AWS

This template demonstrates how to develop and deploy a simple Python Flask API service running on AWS Lambda using the traditional Serverless Framework.

Anatomy of the template

This template configures a single function, api, which is responsible for handling all incoming requests thanks to configured http events. To learn more about http event configuration options, please refer to http event docs. As the events are configured in a way to accept all incoming requests, Flask framework is responsible for routing and handling requests internally. The implementation takes advantage of serverless-wsgi, which allows you to wrap WSGI applications such as Flask apps. To learn more about serverless-wsgi, please refer to corresponding GitHub repository. Additionally, the template relies on serverless-python-requirements plugin for packaging dependencies from requirements.txt file. For more details about serverless-python-requirements configuration, please refer to corresponding GitHub repository.

Usage

Prerequisites

In order to package your dependencies locally with serverless-python-requirements, you need to have Python3.8 installed locally. You can create and activate a dedicated virtual environment with the following command:

python3.8 -m venv ./venv
source ./venv/bin/activate

Alternatively, you can also use dockerizePip configuration from serverless-python-requirements. For details on that, please refer to corresponding GitHub repository.

Deployment

This example is made to work with the Serverless Framework dashboard, which includes advanced features such as CI/CD, monitoring, metrics, etc.

In order to deploy with dashboard, you need to first login with:

serverless login

install dependencies with:

npm install

and

pip install -r requirements.txt

and then perform deployment with:

serverless deploy

After running deploy, you should see output similar to:

erverless: Using Python specified in "runtime": python3.8
Serverless: Packaging Python WSGI handler...
Serverless: Generated requirements from /home/xxx/xxx/xxx/examples/aws-python-flask-api/requirements.txt in /home/xxx/xxx/xxx/examples/aws-python-flask-api/.serverless/requirements.txt...
Serverless: Using static cache of requirements found at /home/xxx/.cache/serverless-python-requirements/62f10436f9a1bb8040df30ef2db5736c8015b18256bf0b6f1b0cbb2640030244_slspyc ...
Serverless: Packaging service...
Serverless: Excluding development dependencies...
Serverless: Injecting required Python packages to package...
Serverless: Creating Stack...
Serverless: Checking Stack create progress...
........
Serverless: Stack create finished...
Serverless: Uploading CloudFormation file to S3...
Serverless: Uploading artifacts...
Serverless: Uploading service aws-python-flask-api.zip file to S3 (1.3 MB)...
Serverless: Validating template...
Serverless: Updating Stack...
Serverless: Checking Stack update progress...
.................................
Serverless: Stack update finished...
Service Information
service: aws-python-flask-api
stage: dev
region: us-east-1
stack: aws-python-flask-api-dev
resources: 12
api keys:
  None
endpoints:
  ANY - https://xxxxxxx.execute-api.us-east-1.amazonaws.com/dev/
  ANY - https://xxxxxxx.execute-api.us-east-1.amazonaws.com/dev/{proxy+}
functions:
  api: aws-python-flask-api-dev-api
layers:
  None

Note: In current form, after deployment, your API is public and can be invoked by anyone. For production deployments, you might want to configure an authorizer. For details on how to do that, refer to http event docs.

Invocation

After successful deployment, you can call the created application via HTTP:

curl https://xxxxxxx.execute-api.us-east-1.amazonaws.com/dev/

Which should result in the following response:

{"message":"Hello from root!"}

Calling the /hello path with:

curl https://xxxxxxx.execute-api.us-east-1.amazonaws.com/dev/hello

Should result in the following response:

{"message":"Hello from path!"}

If you try to invoke a path or method that does not have a configured handler, e.g. with:

curl https://xxxxxxx.execute-api.us-east-1.amazonaws.com/dev/nonexistent

You should receive the following response:

{"error":"Not Found!"}

Local development

Thanks to capabilities of serverless-wsgi, it is also possible to run your application locally, however, in order to do that, you will need to first install werkzeug dependency, as well as all other dependencies listed in requirements.txt. It is recommended to use a dedicated virtual environment for that purpose. You can install all needed dependencies with the following commands:

pip install werkzeug
pip install -r requirements.txt

At this point, you can run your application locally with the following command:

serverless wsgi serve

For additional local development capabilities of serverless-wsgi plugin, please refer to corresponding GitHub repository.