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Add FastAPI Background Tasks example (#408)
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‎README.md

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@@ -167,6 +167,7 @@ The Lambda Web Adapter also supports all non-HTTP event triggers, such as SQS, S
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- [FastAPI](examples/fastapi)
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- [FastAPI in Zip](examples/fastapi-zip)
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- [FastAPI with Background Tasks](examples/fastapi-background-tasks)
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- [FastAPI with Response Streaming](examples/fastapi-response-streaming)
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- [FastAPI with Response Streaming in Zip](examples/fastapi-response-streaming-zip)
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- [Flask](examples/flask)

‎examples/fastapi-background-tasks/.gitignore

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‎examples/fastapi-background-tasks/README.md

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# FastAPI Background Task example
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A basic FastAPI application example. You can build and test it locally as a typical FastAPI application.
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Using AWS Lambda Web Adapter, You can package this web application into Docker image, push to ECR, and deploy to Lambda, ECS/EKS, or EC2.
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The application can be deployed in an AWS account using the [Serverless Application Model](https://github.com/awslabs/serverless-application-model). The `template.yaml` file in the root folder contains the application definition.
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The top level folder is a typical AWS SAM project. The `app` directory is a FastAPI application with a [Dockerfile](app/Dockerfile).
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```dockerfile
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FROM public.ecr.aws/docker/library/python:3.12-slim
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COPY --from=public.ecr.aws/awsguru/aws-lambda-adapter:0.8.1 /lambda-adapter /opt/extensions/lambda-adapter
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ENV PORT=8000
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WORKDIR /var/task
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COPY requirements.txt ./
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RUN python -m pip install -r requirements.txt
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COPY *.py ./
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CMD exec uvicorn --port=$PORT main:app
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```
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Line 2 copies lambda web adapter binary into /opt/extensions. This is the change to run the FastAPI application on Lambda.
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```dockerfile
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COPY --from=public.ecr.aws/awsguru/aws-lambda-adapter:0.8.1 /lambda-adapter /opt/extensions/lambda-adapter
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```
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## Pre-requisites
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The following tools should be installed and configured.
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* [AWS CLI](https://aws.amazon.com/cli/)
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* [SAM CLI](https://github.com/awslabs/aws-sam-cli)
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* [Python](https://www.python.org/)
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* [Docker](https://www.docker.com/products/docker-desktop)
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## Deploy to Lambda
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Navigate to the sample's folder and use the SAM CLI to build a container image
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```shell
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$ sam build
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```
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This command compiles the application and prepares a deployment package in the `.aws-sam` sub-directory.
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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
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```shell
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$ sam deploy --guided
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```
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Please take note of the container image name.
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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
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```shell
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...
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---------------------------------------------------------------------------------------------------------
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OutputKey-Description OutputValue
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---------------------------------------------------------------------------------------------------------
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FastAPIURL - URL for application https://xxxxxxxxxx.execute-api.us-west-2.amazonaws.com/
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---------------------------------------------------------------------------------------------------------
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...
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$ curl https://xxxxxxxxxx.execute-api.us-west-2.amazonaws.com/
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```
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## Run the docker locally
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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.
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```shell
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$ docker run -d -p 8000:8000 {ECR Image}
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```
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Use curl to verify the docker container works.
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```shell
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$ curl localhost:8000/
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```

‎examples/fastapi-background-tasks/__init__.py

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‎examples/fastapi-background-tasks/app/Dockerfile

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FROM public.ecr.aws/docker/library/python:3.12-slim
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COPY --from=public.ecr.aws/awsguru/aws-lambda-adapter:0.8.1 /lambda-adapter /opt/extensions/lambda-adapter
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ENV PORT=8000
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WORKDIR /var/task
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COPY requirements.txt ./
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RUN python -m pip install -r requirements.txt
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COPY *.py ./
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CMD exec uvicorn --port=$PORT main:app

‎examples/fastapi-background-tasks/app/__init__.py

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‎examples/fastapi-background-tasks/app/background.py

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from threading import Thread
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from queue import Queue
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import json
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import os
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import requests
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class BackgroundTaskExtension(Thread):
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def __init__(self):
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super().__init__()
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self.daemon = True
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self.queue = Queue()
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self.session = requests.Session()
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self.start()
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def run(self):
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# start an internal extension
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response = self.session.post(
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url=f"http://{os.environ['AWS_LAMBDA_RUNTIME_API']}/2020-01-01/extension/register",
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json={'events': ['INVOKE'],},
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headers={'Lambda-Extension-Name': 'background-task-extension' }
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)
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extension_id = response.headers['Lambda-Extension-Identifier']
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while True:
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response = self.session.get(
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url=f"http://{os.environ['AWS_LAMBDA_RUNTIME_API']}/2020-01-01/extension/event/next",
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headers={'Lambda-Extension-Identifier': extension_id},
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timeout=None
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)
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event = json.loads(response.text)
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if event['eventType'] == 'INVOKE':
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while True:
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message = self.queue.get()
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if message['type'] == 'TASK':
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task, args, kwargs = message['task']
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task(*args, **kwargs)
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if message['type'] == 'DONE':
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break
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def add_task(self, background_task, *args, **kwargs):
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self.queue.put( {"type": "TASK",
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"task": (background_task, args, kwargs)} )
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def done(self):
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self.queue.put( {"type": "DONE"} )

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