Building a REST API with AWS API Gateway & Lambda

In my last post I covered the overall architecture we are building and how to get setup with SAM CLI locally & deploy the app to AWS.

Setting up a virtual environment

Since we will be using python to build our app, lets create a virtual environment where we can install all our dependencies.

Create a new virtual environment -

python -m venv venv

Activate the environment

source venv/bin/activate

Install the dependencies

pip install -r src/requirements.txt

Customize the application

Rename the folder “hello_world” to “src”

Rename app.py to create.py

In the Dockerfile, update the reference to app.py and remove the CMD statement. The Dockerfile should look like this -

FROM public.ecr.aws/lambda/python:3.9
COPY create.py ${LAMBDA_TASK_ROOT}
COPY requirements.txt ${LAMBDA_TASK_ROOT}
RUN python3.9 -m pip install -r requirements.txt -t .

Update the contents of template.yml to the following -

We now update create.py to accept a POST request and return a request ID for tracking.

Build & test the app

Build the app with the following command -

sam build

Test the app locally, run the following command to expose the endpoint -

sam local start-api

You should see the following output -

We can now test the endpoint by making a POST request using POSTMAN with the request body -

{
   "url": "https://www.google.com/search?q=random+search"
}

The response back should contain the url and a request_id -

Deploy the app

Deploy the app to AWS using the following command -

sam deploy --guided

If you followed the steps from my previous post, you should already have a samconfig.toml file generated. Delete that file before running the above command so that we can setup our deploy config from scratch.

Choose the following options in the interactive session -

If the deployment succeeded, you should see the following output -

This will create the samconfig.toml file again with the configs stored. For subsequent deployments you can simply run sam deploy to deploy the app.

Testing the deployed app

Use the API URL from the output and test the POST call from postman.

Note: The url should be copied from the output as-is. The url is case-sensitive and any trailing spaces can also result in a 403 response.

Source Code

Here is the source code for the project created here.

Next: Part 3: Storing AWS SQS messages to DynamoDB with AWS Lambda