Synapse Balancer

Uses synapse to expose Docker web apps to ELBs

Purpose

1. Allows a pinned port to be exposed to ELBs (they can only configured to look for back-end listener on specific ports, and they don't seem to be particularly resilient to changing conditions among their listeners).
2. Allows us to deploy new web app containers without dropping connections. Since the ELBs need pinned ports for their back-ends, you can't easily spin up a new container while the old one is still running. This balances connections between old and new during that period.
3. Translates public URLs to Immutant-friendly URLs via its synapse/haproxy config. For example, it will translate http://ballotscout.org/foo?bar=1 to http://[immutant-host]:8080/ballot-scout/foo?bar=1.

Usage

1. Put your config file in conf/config.json
2. docker build -t quay.io/democracyworks/synapse-balancer .
3. docker run -d -p 60800:80 quay.io/democracyworks/synapse-balancer

Multiple configs

If you want to support more than one config in different environments, you have a couple of different options:

1. Bake in multiple config files and choose one at runtime:
   1. Put your configs (named anything you want) in the conf dir.
   2. Build a new Docker image to pick up your configs.
   3. Append the name of your config file to the end of the docker run command (WITHOUT the conf/ prefix).
2. Mount your config(s) as a volume:
   1. In your docker run command, add a --volume /path/to/your/configs:/usr/src/synapse-balancer/conf and then append the filename of the config file you want to run to your docker run command.