Java Debug Buildpack

About

Proof-of-concept Cloud Foundry buildpack for collecting debug information about java applications at runtime.

How it Works

This buildpack adds a sidecar process to any application built with it. The sidecar is a simple web server. If a route is mapped to the web server and an HTTP request is issued to it, then the sidecar collects a java thread dump from the running java application.

Usage

1. Build the sidecar binary

   $ GOOS=linux GOARCH=amd64 go build java_debug_sidecar.go
   

2. Zip it up:

   # from the root of this repo, zip up buildpack excluding the .git directory 
   $ zip -r java-debug-buildpack.zip . -x "*.git*"
   

3. Upload the buildpack to cloudfoundry

   $ cf create-buildpack java_debug_buildpack java-debug-buildpack.zip <index>
   

4. Push a java app

   $ cd <app-rootdir>
   # note the debug buildpack cannot be the final buildpack
   $ cf push my-app -b java_debug_buildpack -b java_buildpack
   

In a real use case, you would set up an external route to the sidecar via the v3 API, but it is not currently well-supported via the CLI. For simplicity, it's easier to ssh in and call the sidecar on localhost:

$ cf ssh my-app
...
$ curl localhost:8081/threaddump

The thread dump will then be added to the app's logs.