add auth server

[vladikoff]

@jbuck @seanmonstar so we have this thing where auth-server requires db to start first.

I added these depends_on and a healthcheck options so db-mysql starts first. However it is not working. Ref: https://docs.docker.com/compose/compose-file/#healthcheck

Also see this: docker/compose#374 (comment)

Related for version 3 of compose files, this won't be supported:

Basically, it won't be supported, you have to make your containers fault-tolerant instead of relying on docker-compose. ~ docker/compose/issues/374#issuecomment-285156051

Which means we will need to patch the auth-server later on...

[seanmonstar]

So, being forward thinking and assuming we want to use v3, we can't have a boot order. This means we need to add to the auth-server the ability to keep trying to reconnect to the database? That seems reasonable anyways: the server shouldn't fall over and die if mysql is burning. It likely just returns 500 errors.

I'd imagine we could update the auth server to start up right away, and the healthcheck just returns 500s for as long as the mysql server is not running. Once mysql comes up, another healthcheck of the auth should give us a 200 as it successfully pings the db server.

[seanmonstar]

@vladikoff so, I'm trying this out in https://github.com/mozilla/fxa-auth-server/tree/db-tolerant. I'm looking in to see if we can teach the Pool to always check the api version when connecting a new socket, but the branch should already work fine without it.

[vladikoff]

@seanmonstar also see mozilla/fxa-auth-server#1709 there is a ref to what mailer already does

[seanmonstar]

@vladikoff I'm feeling it's cleaner to just allow the auth server to stand on its own. Checking the /__heartbeat__ will let us see if its currently in a speaking relationship with the db server or not.