FastAPI Lambda POC

Content

• About
• Setup
  • Initialize Terraform
  • Package Lambda Code
  • Deploy
  • Take Down
• Testing the App

About

This is a small POC / template for deploying a FastAPI application to AWS lambda and exposing it via API gateway. The app is quite simple and contains a single GET endpoint, a single POST endpoint, and a documentation URL. The app's infrastructure is deployed and managed using terraform.

Setup

In order to set up the POC, first ensure you have the AWS credentials necessary for the deployment, and that you have Python 3.9 installed in your working environment. You must also have a Linux OS to run the packaging and deployment, since AWS lambda runs on AmazonLinux. The setup is handled using Task to handle tasks.

Initialize Terraform

The first thing you should do before deploying is to initialize Terraform for the project's infrastructure. To do this, you can run task terraform init if you have Task installed. If you don't, go to the infrastructure directory and run terraform init.

Package Lambda Code

Next, you must package the lambda function's code and library dependencies in a zip file that can be uploaded to AWS. If you have Task, you can do this by running task package-lambda.

Deploy

Finally, to deploy the infrastructure to AWS using terraform, you can run task deploy. If you are too impatient to run the two steps above separately, you can run this command from the start, and it will run the others as dependencies. Once terraform has deployed the app, it will output the docs URL to the terminal. You can then go to this URL to play around with the endpoints.

Take Down

Once you are done with the app, you can take it down from AWS by running task take-down to delete the infrastructure.

Testing the App

Once the app is deployed, you can test it by hitting the API endpoints or by consulting the docs URL. The API endpoints require you to send an API Key under the x-api-key header. This key is generated by AWS and is output by terraform after deploying (this is a sensitive output, so it won't show up in the console). To view it, run terraform output api_key in the infrastructure directory.

Once you have fetched the key and the invoke URL from the terraform outputs, you can cunsult the endpoints with:

import requests

endpoint_url = "{invoke-url}"
api_key = "{api-key}"

# Get endpoint
rsp = requests.get(
    "%s/dev/api/v1/add-numbers" % endpoint_url,
    params={"a": 1, "b": 2},
    headers={"x-api-key": api_key}
)
print(rsp, rsp.json())

# Post endpoint
rsp = requests.post(
    "%s/dev/api/v1/add-numbers" % endpoint_url,
    json={"a": 1, "b": 2},
    headers={"x-api-key": api_key}
)

print(rsp, rsp.json())

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