How to setup a buildfarm for my git repo ?

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What exactly I'm trying to achieve here ?

I have a git repo with me that takes in the camera images and estimates user pose, saves data and trains a classifier. I want to setup a build farm for this repo, perform continuous integration and post build steps. Oh ! and also, please let me know if this is possible with the ros buildfarm. Provide documentation that clearly explains what to do if someone like me wants to setup a buildfarm.

Depending on your end-goal, it may be easier to begin either without ros_buildfarm or using ros_buildfarm without a full buildfarm deployment:

A. Running your repositories tests.
If all you want is basic continuous testing, setting up an entire buildfarm might be overkill. There are examples of setting up ROS repositories in Travis. This repository provides a sample .travis.yml and information for doing exactly that. It might be a bit stale and it's not something I've worked with, but once set up, it would run your tests without the need for running your own buildfarm. MoveIt! has a CI repository with an up-to-date Travis config as well. (Hat tip to @Geoff in the comments).

B. If you also want to build binary packages for your repository, it's still possible to do without setting up a buildfarm deployment, but you will need to create suitable rosdistro and ros_buildfarm_config configuration files so that the ros_buildfarm scripts can be run on your local machines.

C. Of course, you can also set up a complete buildfarm cluster to perform run ros_buildfarm operations. This is probably the best option if you're going to be adding more custom packages down the road or building for multiple rosdistros. It's also the course of action you're already on.

ARM build agents

I thought of having a Jetson Tx2 as my agent and a Raspberry Pi 3 B as my repo but I'm willing to change this to two more VMs having same specs as my master.

I mentioned in your previous question that the buildfarm_deployment repository was originally written for x86 hosts only and that I know it doesn't support arm64 hosts out of the box and it probably won't work on a Raspberry Pi running Raspbian Stretch or even Ubuntu Xenial. I have deployed arm64 agents but I had to do the last 40% of the setup by hand which requires some experience and understanding of what the Puppet config management is doing for you so it won't be straightforward if you're new to Puppet and ros_buildfarm. You also won't be able to build for AMD64 (x86_64) targets with an arm64 agent, though you can build for arm64 with an AMD64 host using qemu, which the buildfarm_deployment sets up by default.

I would recommend using AMD64 virtual machines although they don't all need to be as powerful as your Jenkins master. This document has some recommended instances sizes using AWS instances sizes as a ... (more)