For your own safety don't use this in production without a ton of testing

A quick and dirty solution to tracking Marathon instances. It stores the ${MESOS_TASK_ID} in a comma (,) separated list under /instance-tracker/${MARATHON_APP_ID} in Zookeeper

Build: go build -o instance-tracker *.go

Requires the following environment variables:

MARATHON_URL=http://yourmarathonurl.com:8080
PORT=9090
HOST=host_that_hosts_this_app
ZK_SERVERS=127.0.0.1:2181

$HOST, $MARATHON_URL and ZK_SERVERS need to be resolvable from Marathon as well as the server running this application.

Use something like go-zkCli to get the value from Zookeeper. See the included getMyId.sh for an example.

• Sort out a working docker container
• Make sure it handles situations where znodes are locked
• Figure out a way to handle upgrade situations where momentarily INSTANCES is INSTANCES+1
• Clean up the messy code
• Write some tests

• This article by Cory Lanou helped me get started with creating a REST service.
• This article by Mark McGranaghan helped me get started with using Zookeper from Go.