Adding documentation for setting up a developer environment.

docs/developing.md

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+
+# Developing gorealis
+
+
+### Installing Docker
+
+For our developer environment we leverage of Docker containers.
+
+First you must have Docker installed.  Instructions on how to install Docker
+vary from platform to platform and can be found [here](https://docs.docker.com/install/).
+
+### Installing docker-compose
+
+To make the creation of our developer environment as simple as possible, we leverage
+docker-compose to bring up all independent components up separately.
+
+This also allows us to delete and recreate our development cluster very quickly.
+
+To install docker-compose please follow the instructions for your platform
+[here](https://docs.docker.com/compose/install/).
+
+
+### Getting the source code
+
+As of go 1.10.x, GOPATH is still relevant. This may change in the future but
+for the sake of making development less error prone, it is suggested that the following
+directories be created:
+
+`$ mkdir -p $GOPATH/src/github.com/paypal`
+
+And then clone the master branch into the newly created folder:
+
+`$ cd $GOPATH/src/github.com/paypal; git clone git@github.com:paypal/gorealis.git`
+
+Since we check in our vendor folder, gorealis no further set up is needed.
+
+### Bringing up the cluster
+
+To develop gorealis, you will need a fully functioning Mesos cluster along with
+Apache Aurora.
+
+In order to bring up our docker-compose set up execute the following command from the root
+of the git repository:
+
+`$ docker-compose up -d`
+
+### Testing code
+
+Since Docker does not work well using host mode under MacOS, a workaround has been employed:
+docker-compose brings up a bridged network.
+
+* The ports 8081 is exposed for Aurora. http://localhost:8081 will load the Aurora Web UI.
+* The port 5050 is exposed for Mesos. http://localhost:5050 will load the Mesos Web UI.
+
+#### Note for developers on MacOS:
+Running the cluster using a bridged network on MacOS has some side effects.
+Since Aurora exposes it's internal IP location through Zookeeper, gorealis will determine
+the address to be 192.168.33.7. The address 192.168.33.7 is valid when running in a Linux
+environment but not when running under MacOS. To run code involving the ZK leader fetcher
+(such as the tests), a container connected to the network needs to be launched.
+
+For example, running the tests in a container can be done through the following command from
+the root of the git repository:
+
+`$ docker run -t -v $(pwd):/go/src/github.com/paypal/gorealis --network gorealis_aurora_cluster golang:1.10.3-alpine  go test github.com/paypal/gorealis`
+
+Or
+
+`$ ./runTestsMac.sh`
+
+Alternatively, if an interactive shell is necessary, the following command may be used:
+`$ docker run -it -v $(pwd):/go/src/github.com/paypal/gorealis --network gorealis_aurora_cluster golang:1.10.3-alpine /bin/sh`
+
+### Cleaning up the cluster
+
+If something went wrong while developing and a clean environment is desired, perform the
+following command from the root of the git directory:
+
+`$ docker-compose down && docker-compose up -d`
+
+
+### Tearing down the cluster
+
+Once development is done, the environment may be torn down by executing (from the root of the
+git directory):
+
+`$ docker-compose down`
+
+
+