sam-building-custom-runtimes-java

This project is a sample about how to use AWS SAM Building Custom Runtimes feature to build a java8 maven project. I have created this repo to help Java developers, since I couldn't find a reference specific for maven projects.

By default AWS SAM cli build command will perform an mvn clean install (reference here). It may not be enough for some use cases which we need custom maven commands, for example to enable/disable some maven plugin. More information about SAM build flow could be found here.

To build a custom runtime, declare the Metadata resource attribute with a BuildMethod: makefile entry. You provide a custom makefile, where you declare a build target of the form build-function-logical-id that contains the build commands for your runtime

Resources:
  HelloWorldFunction:
    Type: AWS::Serverless::Function
    Metadata:
      BuildMethod: makefile
    ...

Make sure to create a custom makefile and add it in the same folder than your lambda's code.

build-HelloWorldFunction:
	@ mvn clean install # Add here your custom commands
	@ mvn dependency:copy-dependencies -DincludeScope=compile
	@ cp -rf ./target/classes/* $(ARTIFACTS_DIR)/
	@ mkdir -p $(ARTIFACTS_DIR)/lib
	@ cp -rf ./target/dependency/* $(ARTIFACTS_DIR)/lib
	@ rm -rf ./target

Also make sure to add all those steps, since SAM requires them to be able to run it locally. From AWS doc:

Your makefile is responsible for compiling the custom runtime if necessary, and copying the build artifacts into the proper location required for subsequent steps in your workflow.

References:

• What is SAM?
• AWS SAM Building Custom Runtimes feature
• AWS Lambdas builders repo
• AWS SAM Cli repo