REST API creation in AWS - Commands & Configuration

Introduction

Creating a REST API lets you build a way for different programs to talk to each other over the internet. AWS provides a service called API Gateway that helps you create and manage these APIs easily without managing servers.

When you want to let a mobile app get data from your backend securely.

When you need to connect a web app to a database through a simple interface.

When you want to expose some functions of your service to other developers.

When you want to create a serverless backend that scales automatically.

When you want to manage and monitor API usage and control access.

Config File - template.yaml

template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
  MyApi:
    Type: AWS::Serverless::Api
    Properties:
      StageName: prod
      DefinitionBody:
        openapi: 3.0.1
        info:
          title: MySampleAPI
          version: '1.0'
        paths:
          /hello:
            get:
              x-amazon-apigateway-integration:
                uri: !Sub arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${HelloFunction.Arn}/invocations
                httpMethod: POST
                type: aws_proxy
              responses: {}
  HelloFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: index.handler
      Runtime: nodejs18.x
      CodeUri: ./src/
      Policies: AWSLambdaBasicExecutionRole
      Events:
        HelloApi:
          Type: Api
          Properties:
            RestApiId: !Ref MyApi
            Path: /hello
            Method: get

This AWS SAM template defines a simple REST API with one GET endpoint /hello. It uses AWS Lambda as the backend function. The MyApi resource creates the API Gateway REST API. The HelloFunction resource is the Lambda function that handles requests. The x-amazon-apigateway-integration section connects the API Gateway to the Lambda function using a proxy integration.

Commands

This command builds your AWS Serverless Application Model (SAM) project, preparing the Lambda function code and dependencies for deployment.

Terminal

sam build

Expected Output

Building codeuri: ./src runtime: nodejs18.x metadata: {} architecture: x86_64 functions: ['HelloFunction']

Running NodejsNpmBuilder:CopyNpmrc

Running NodejsNpmBuilder:Build

Build Succeeded

This command deploys your SAM application to AWS. The guided flag helps you set parameters like region, permissions, and confirms before deploying.

Terminal

sam deploy --stack-name my-sample-api --guided

Expected Output

Configuring SAM deploy

======================

Stack Name [sam-app]: my-sample-api

AWS Region [us-east-1]: us-east-1

Confirm changes before deploy [y/N]: N

Allow SAM CLI IAM role creation [Y/n]: Y

Save arguments to samconfig.toml [Y/n]: Y



Deploying with following values

===============================

Stack name: my-sample-api

Region: us-east-1

Confirm changeset: false

Deployment s3 bucket: sam-cli-managed-default-samclisourcebucket-abc123

Capabilities: ['CAPABILITY_IAM']



Waiting for stack create/update to complete

Successfully created/updated stack - my-sample-api



Outputs

--------

MyApiEndpoint: https://abc123.execute-api.us-east-1.amazonaws.com/prod/

→

--stack-name - Names the CloudFormation stack for your deployment

→

--guided - Interactive mode to help configure deployment settings

This command tests the deployed REST API by sending a GET request to the /hello endpoint. It verifies that the API is working and the Lambda function responds.

Terminal

curl https://abc123.execute-api.us-east-1.amazonaws.com/prod/hello

Expected Output

"Hello from Lambda!"

Key Concept

If you remember nothing else from this pattern, remember: API Gateway connects internet requests to backend Lambda functions to create scalable REST APIs without managing servers.

Common Mistakes

Not deploying the API after building the SAM project

Building prepares the code but does not make it live; without deployment, the API won't be accessible.

Always run 'sam deploy' after 'sam build' to publish your API.

Using the wrong API endpoint URL when testing

The endpoint URL changes with each deployment; using an old or incorrect URL results in connection errors.

Copy the API endpoint URL from the deployment output and use it exactly in your test commands.

Forgetting to grant Lambda permission to be invoked by API Gateway

Without this permission, API Gateway cannot trigger the Lambda function, causing errors.

Use AWS SAM or CloudFormation which automatically sets this permission, or add it manually if deploying differently.

Summary

Use an AWS SAM template to define a REST API and Lambda function integration.

Build the project with 'sam build' to prepare your code for deployment.

Deploy the API with 'sam deploy --guided' to create the live API Gateway endpoint.

Test the API by sending HTTP requests to the deployed endpoint URL.