Moving to docker swarm

[zhengyao-lin]

Since we have containerized broadway API and grader, it would be a natural step to migrate the entire cluster to docker swarm (or other container orchestration system).

This is mostly an issue of configuration. There are a few things to solve in my limited experience with docker swam:

• broadway grader needs to interact with a docker daemon. dind doesn't work in this case since there are some permission issues (docker swam doesn't allow privileged container).
• broadway API need a mongodb instance. So we also need to figure out how to expose a mongodb service to the containers in docker swarm.

A few potential benefits in doing this:

• auto-deployment
• more fault-tolerancy
• easier to monitor the status of the entire cluster (?)