What is it?

Holy lambda is a micro framework which adds support for running Clojure on the AWS Lambda and might be used with arbitrary AWS Lambda deployment tool. Holy lambda provides very convenient environment compared to other tools such as uswitch/lambada or babashka-lambda via simple, but powerful bb tasks recipes eg. deployment is as easy as running bb stack:sync && bb stack:compile && bb stack:pack && bb stack:deploy).

Holy lambda supports

• interceptors
• ring request, response model
• async handlers

Java runtime

Prior work towards targeting Java runtime was done by uswitch/lambada, but lacked being convenient. Holy lambda in the other hand is very convenient and does things which lambada lacked:

• full class identifier is created during macro expansion of deflambda
• request is automatically slurped and converted to a map
• response mimics Ring therefore you don't have to write to OutputStream.
• supports interceptors
• converts ctx

Native runtime

I've started experimenting with native runtime around May 2019 inspired by @hjhamala blog post. At that time Clojure community just started experimenting with GraalVM, and there was not such great tools as babashka, therefore holy-lambda is not babashka based. There are some benefits of not using babashka and some tradeoffs which have to be understood before taking a right decision.

Benefits

• lambdas will be faster in general, because code is not interpreted (benchmarks in-progress)
• use any GraalVM Clojure compatible library. Not only one from limited pool of babashka's pods
• target both Java & native runtime
• mix GraalVM supported languages freely (polyglot)
• use Profile-Guided Optimizations on GraalVM EE PGO

Tradeoffs

• you have to generate native-configurations for GraalVM (automated by running bb native:conf)
• GraalVM compilation is long - for development use Java runtime with sam invoke or bb stack:invoke
• adding and using new library is not always easy when compiling to native, some extra know-how about GraalVM is needed

Babashka runtime

Babashka runtime provides interactive development environment. There is no need for compiling the sources since those are provided as is to AWS SAM.

Runtime	Cold start	Performance	Artifacts size	Memory Consumption	Interactive	Compile time
:native	low	high	high >= 16mb	low	No	very long
:babashka	low	moderate	low >= 50kb	low	Yes	no compile
:java	high	high	moderate >= 12mb	high	No	long

If you're not interested in trying holy-lambda out then you can check very minimal babashka runtime :) babashka-lambda.