How to make a Serverless Application Model in AWS

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In this blog, we’ll learn how to create, build, and test a serverless application model using the CLI. So, let’s get started.

The AWS Serverless Application Model (SAM) is an open-source framework for developing serverless applications on Amazon Web Services.

It allows us to express functions, APIs, databases, and event source mappings using shorthand syntax. We can define and model our application using YAML with just a few lines per resource. SAM converts and expands SAM syntax into AWS CloudFormation syntax during deployment, allowing us to build serverless applications faster.

Prerequisites

  • AWS Account
  • Python 3.9
  • Docker, for testing the application locally
  • Homebrew, for Linux and macOS

Step 1: Install the SAM CLI

Download  AWS SAM CLI zip file zip file.

Using the following command, generate a hash value to verify the integrity and authenticity of the downloaded installer files:

sha256sum aws-sam-cli-linux-x86_64.zip

Unzip the installation files.

unzip aws-sam-cli-linux-x86_64.zip -d sam-installation

Install the AWS SAM CLI.

sudo ./sam-installation/install

Verify the installation.

sam --version

Step 2: Create a SAM Project

For initializing the SAM application run,

sam init 

There will be some on-screen prompts, so for this example, I’ll choose AWS Quick Start Templates, the runtime and zip package type, and a Hello World Example.

Give a name to the project and it will start cloning and generate the application.

This will create a directory with the same name as the project name we specified. The following is a list of the contents of the project directory:

There are three files that are important:

  • template.yaml: Contains the AWS SAM template that defines the AWS resources used by our application.
  • hello_world/app.py: Contains the logic for our Lambda handler.
  • hello_world/requirements.txt: Used for sam build and contains any Python dependencies that the application requires.

Step 3: Build SAM Application

Move to the project directory, where the sample application’s template.yaml file is located and run this command.

sam build

Here, to construct our dependencies, the AWS SAM CLI comes with abstractions for a number of Lambda runtimes and transfers the source code into staging folders so that everything is ready to be packaged and deployed. The sam build command compiles our application’s dependencies and moves our source code to folders under .aws-sam/build, where it will be packaged and published to Lambda.

Step 4: Test SAM Application locally

We may find it handy to test locally when developing our application. The sam local command in the AWS SAM CLI allows us to run our application in Docker containers that simulate Lambda’s execution environment.

There are two ways to do it:

  • Host our API locally
  • Invoke our Lambda function directly

Host our API locally

Run this command.

sam local start-api

The Docker image may take some time to load. We can browse a request to our application after it has loaded.

http://127.0.0.1:3000/hello

Here, the start-api command creates a local endpoint that serves as a replica of our REST API endpoint. It downloads a local execution container in which we can run our function. The end result is the same as when we used the AWS Cloud to invoke our function.

Invoke our Lambda function directly

Run this command.

sam local invoke "HelloWorldFunction" -e events/event.json

The invoke command calls our Lambda functions directly and accepts input event payloads from us.

Conclusion

In this blog, we have learned how to create, build and test our SAM Application. If you have any doubt you can reach out to me.

To read more about DevOps.

HAPPY LEARNING!!

Reference

AWS SAM

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