Running on Kubernetes

Introduction
This wiki will outline how we plan to orchestrate the execution of CDAP programs on top of Kubernetes.

Summary

Kubernetes requires that a Docker image be created in order to run something, so the process of executing a program will look like:

1. Create a Docker image from the program jar and its dependencies.
2. Upload this image to a local repository.
3. Point Kubernetes to this image and execute the program.

Creating the Docker image (options)

1. Java Programmatic API around Docker client: https://github.com/docker-java/docker-java.
2. Bazel - Java-based build system that can build Docker images.
   See also: https://medium.com/bitnami-perspectives/building-docker-images-without-docker-c619061b13a9
   See also: https://blog.bazel.build/2015/07/28/docker_build.html
3. Construct a docker command string and leverage shell utilities from Java.

Hosting the Docker image (options)

1. Docker Registry - a stateless server-side application used for storing and distributing Docker images.
2. Docker Hub - might be too heavyweight and reliant on external services for our use case.
3. Quay (from CoreOS) - not free or open source, so not high on the list.

Miscellaneous

• There is an experimental project which supports running Spark programs on Kubernetes. "The feature set is currently limited and not well-tested. This should not be used in production environments." https://apache-spark-on-k8s.github.io/userdocs/running-on-kubernetes-cloud.html

• MR on Kubernetes seems to be project with very little usage. "This is not robust code. Do not use in production.": https://github.com/turbobytes/kubemr

• To get familiar with how Docker works:
  • How to Dockerize Java RESTful API Application
  • Dockerize Your Java Application

TODO:

• Have some numbers around building a Docker image.
• How can Kubernetes be the runtime under the Twill API, instead of YARN? What are the issues with this integration? What in the Twill API can't be supported?
• Is there a programmatic API (or at least RESTful) around Kubernetes command-line?
• How can CDAP master talk to the Kubernetes master to get program status (or any of the Kubernetes interactions)?
• How long will a Docker image take to run a CDAP program - with and without a base image that has as much as possible of the common stuff?
• How can we leverage functionality in Kubernetes to avoid a dependency on Zookeeper? Or should we just use etcd regardless of whether we're using Kubernetes or not?
• Do we need provisioner hooks? For instance, to kick off an instance of Docker Registry after provisioning a Kubernetes cluster?
• Do research about difficulty of use for YARN vs Kubernetes, ZooKeeper vs etcd.