Automation hooks?

Rancher 1.x
1

I’m working on a way to automate the creation of new hosts on demand. So if someone wants to run
a container or group of containers, but there are no resources available, I’d
like to automatically create a new host, then honor their request. Also, if I have a host is sitting around idle for too long,
I’d like to automatically terminate it and free up the resources.
I don’t know how practical this will be, but I’d like to know if Rancher has any hooks in place to facilitate this sort of thing.

2

There are no hooks for these, but deleting hosts that have no containers could be done through the API and would be relatively straightforward I would think.

  • Poll GET /v1/hosts
  • Follow the instances link on each host to get the containers
  • If there are no containers (you’ll want to ignore ones with "systemContainer": "NetworkAgent"), note the time somewhere.
  • Rinse, lather, repeat. If there have been no containers for long enough, call DELETE on the physicalHost link for the host (assuming these hosts were created through Rancher/docker-machine.)

Detecting when to add is more difficult… There’s not anything obvious to detect why scheduling a service container fails, or if adding a host would improve the situation. e.g. there could be no host with port 80 available so adding another host might address that, or there might be a global service that uses port 80 and it will still be unavailable if you add one.