Service discovery and daemons with docker

Question

Here are some questions I have about Docker:

Given the way Docker handles Daemons and Links betweens services (not using daemons)

1- How process monitoring, daemons and application chains will work (ie: upstart/bluepill/unicorn) if you can run daemons and bluepill restarts process by itself ?

2- How will it work with load balancing with a high level proxy when it comes to find ip address of the containers to balance to if you want to stick to upstart/bluepill/unicorn model ?

3- Which is the recommended software for service discovery on the top of docker for example to perform a rails deploy?

Answer 1

1- AFAIK, there is no problem running bluepill (or some other process monitor like supervisor or monit) in a docker container. I often used this kind of tool to run more than one service in a container.

2- For load balancing containers, you can either use a load balancer that you can configure dynamically (for http balancing, hipache is a good candidate) or have some scripts that dynamically update configuration of a standard load balancer and reloads it (I did it many times with nginx, it should work with other solutions)

3- There are some tools in the docker ecosystem for service discovery. You can have a look at Serf (http://www.serfdom.io/) and etcd (https://github.com/coreos/etcd). For the deploy part, I would recommend you to use the ONBUILD instruction in Dockerfile to inject application code and create immutable containers.