Deploying a FastAPI Project on AWS Lambda

Introduction

This guide outlines the steps required to deploy a FastAPI project on AWS Lambda using a separate requirements package and code-only zip file.

Prerequisites:

Before you begin, you will need the following:

1. A sample FastAPI project
2. An AWS account with access to AWS Lambda and S3 services to deploy code

For this example, we will use a FastAPI project named sample-fastapi-project and an S3 bucket named sample-fastapi-s3. We will also create an AWS Lambda function named sample-fastapi-lambda.

Step 1 — Create a virtual environment to isolate our app dependencies.

  $  python3 -m venv venv/

Step 2 – Activate the environment:

  # In Linux, type 
  $  source venv/bin/activate

  # In Windows, type 
  $ .\venv\Scrips\activate

Step 3 – Install dependencies that are required for this project:

  $  pip install -r requiements.txt

Step 4 – Add Mangum to the FastAPI code:

  $ pip install mangum

  $ pip freeze > requiements.txt

Import the Mangum module in your FastAPI code:

  from mangum import Mangum

Wrap the FastAPI app with Mangum:

  app = FastAPI()
  handler = Mangum(app)

Mangum allows us to wrap the API with a handler that we will package and deploy as a Lambda function in AWS.

Step 5 – Create a separate requirements package zip file

  $  pip3 install -r requirements.txt -t ./packages
  $  cd packages
  $  zip -r9 ../requirements.zip .

This will create a seperate requirements.zip file

Step 6 – Create a code-only zip file

Create a separate zip file containing only your project’s code, including the main.py file. Name this file sample-fastapi.zip.

  # if all the code is in main.py file, then
  $  zip sample-fastapi.zip main.py

  # Add other files to created zip if required
  $  zip sample-fastapi.zip -u <python_file>

Step 7 – Upload the requirements package and code-only zip files to S3(sample-fastapi-s3):

Go to the s3 bucket and click on upload icon to uplaod both files directly.

Step 8 – Create a new Lambda function:

1. Navigate to the Lambda service in the AWS Console and click Create function.
2. Select Author from scratch and enter sample-fastapi-lambda as the function name.
3. Choose Python 3.7 as the runtime.
4. If having existing role then under Change default execution role Choose Execution role as Use an existing role and select the role
5. Otherwise Choose Create a new role with basic Lambda permissions and Click create function

Step 9 – Add the requirements package as a Lambda layer:

1. In the Lambda function page, navigate to the Layers section and click Add a layer > Layers > create layer.
2. Choose Upload a file from Amazon S3 and copy the S3 URI of the requirements.zip file that you uploaded to S3 in Step 7.
3. Enter a name for the layer and click Create.

Step 10 – Add the code-only zip file to the Lambda function:

1. In the Lambda function page, navigate to the Function code section and choose Upload from Amazon S3 location under Code source.
2. Copy the S3 ULI of sample-fastapi.zip file that you uploaded to S3 in Step 7.
3. Click Save

Step 11 – Set the Lambda function handler:

1. In the Lambda function page, scroll down to the Runtime settings section and set the handler name to main.handler.
2. It will execute handler function under main.py file.
3. Check Step-4 for reference.

Step 12 – Configure the Lambda function:

In the Lambda function page, navigate to the Configuration section and under General configuration set the following parameters:

1. Memory (RAM): 1024 MB
2. Memory (ROM): 512 MB
3. Timeout: 1 minute

Click on Environment variables

Set any environment variables required by your FastAPI project

In the Lambda function page, scroll down to the Layers > Add layer.

1. Selectcustom layers in layer source
2. Add the requirements-package to layer that you created in Step 9
3. Choose Version and Click Add

Add Function URL

1. In the Lambda function page, navigate to the Configuration section and under Function URL, Click Create function url
2. Set Auth type as None.
3. Click Save

Step 13 – Test the Lambda function:

In the Lambda function page, Copy “Function Url” and test your function in any browser. just add.. <Function Url>/docs in URL

You should see the output from your FastAPI project’s APIs.

Congratulations! You have successfully deployed a FastAPI project on AWS Lambda.