Example Java in AWS Lambda via API Gateway

What's that? You like using Java in IntelliJ, and want to set up a simple API callback service on AWS, without all the bells and whistles of setting up the AWS Toolkit, opting instead for a barebones .jar file that will get the job done quick and fast for cheap? Well you've come to the semi-relevant place!

So what's this repo? A no-nonsense guide to set up some java code to be triggered via http request, without complicated server setup. It features:

Java
- Maven
- IntelliJ (Community Edition)
AWS Lambda
- Run code from an uploaded JAR file.
- Retrieve request parameters.
- Set and read system environment variables.
- CloudWatch Logging.
API Gateway
- Hook AWS lambda up to a HTTP API, which is 2-3 times cheaper than a REST API configuration.

This assumes you have:

Java and IntelliJ (Community Edition)
AWS account (a free one will do)

Step 1: Java + Maven Repository

That's this repository. You can just clone this and skip everything up to the last 3 or so steps.

IntelliJ: File (Alt-F) -> New... (N) -> Project...
Create a new Maven project
- Maven
- [Project SDK] 1.8 java version
Set name and location (here's the setup for this repo)
- [Name] aws-gateway-lambda
- [GroupId] com.flashkirby.examples
- [ArtifactID] aws-gateway-lambda
The project should initialise with a basic Maven set up.
Add the MANIFEST.MF for build properties
Create the main class that will handle the request event. In this repo, this is the Endpoint.java file
- The method, handleRequest, takes information from the request and the lambda context, and returns a response.

Add the Maven dependencies and build information to the pom.xml
- Right click the pom.xml file and Add as Maven Project
- Maven -> Reimport
Maven: aws-gateway-lambda -> Lifecycle -> install
- Open up Maven from the (default) right sidebar
Jar file will be compiled in the /target folder.

Step 2: AWS Lambda

Visit AWS Lambda
Create function
- Author from scratch
- [Function name] gateway-lambda-example
- [Runtime] Java 8
- [Permissions] Create a new role from AWS Policy Templates
- [Role name] example-role-lambda
- [Policy templates - optional] Basic Lambda@Edge permissions (for CloudFront trigger)
  - Grants permissions to use CloudWatch for logging. You can ignore this if you don't want logs.
Set Code entry type to "Upload a .zip or .jar file"
- [Function Package] Upload -> the jar file in your /target folder.
Set the handler to call the correction function
- [Handler] com.flashkirby.examples.awslambda.Endpoint::handleRequest
Set environment variables for this lambda deployment
- Environment variables -> Edit
- Add environment variable
- [Key/Value] TOKEN/secret
- Save
Perform a test against the code by configuring a test event (Next to Save). Here's an example of a HTTP query resembling /gateway-lambda-example?token=hello
- For an in depth look at the structure of request, see the "Version 2.0" heading in this example.

{
    "version": "2.0", 
    "rawPath": "/gateway-lambda-example", 
    "queryStringParameters":
    {
        "token": "hello"
    }
}

Step 3: AWS API Gateway

+ Add Trigger (from the Designer)
[Trigger Configuration] Set API Gateway
Create an API
HTTP API
- for reasons, or if tl/dr...
- faster: "60% latency reduction" (p99 < 10ms)
- cheaper: "~70% cost savings"
  - < 300 Million, $3.50 -> $1.00
  - 20 Billion +,$1.51 -> $0.90
  - "Simpler UI + CORS config"
[Security] Open
- Read more about JWT auth here
Additional Settings, you can set the name of your API here
From API Gateway, navigate to your shiny new API
Call the function with the link in Invoke Url
- Develop -> Routes, to edit the Method and Path of the function being called.
- To test non-GET functions, try Postman

Additional Resources

Change environment variables to API Gateway staging variables [link]

Flashkirby/aws-gateway-lambda

Example Java in AWS Lambda via API Gateway

Step 1: Java + Maven Repository

Step 2: AWS Lambda

Step 3: AWS API Gateway

Additional Resources