Docker Rolling Update

I just worked out another flow to have Zero downtime (mainly for web apps).

Proxy

We use jwilder/nginx-proxy to handle routing to app servers, this will assist us in dynamically routing requests to services.

First Deploy

For the first deploy run docker-compose --project-name=app-0001 up -d.

Rolling Update

We edit the docker-compose.yml with the new image id and run docker-compose --project-name=app-0002 up -d. We now have version 0.2 of the app up and running. The load balancer will already begin routing requests, and given we are using nginx LB we will have 0 downtime.

If you need to reach a desired scale you can now run that command to scale up resources before you shutdown the older version.

Now we can do docker-compose --project-name=app-0001 stop to close down the previous deploy. (Optionally we can run an rm to remove the data - but it might be a good idea to only remove this on the next deploy i.e. deploy app-0003 up, app-0002 stop, app-0001 rm).

Truly rolling update

If you have reasoning behind limiting the number of resources running at a given time you could simply stagger the scale. I.e:

app-0001 scale web=10
...
app-0001 scale web=8 app-0002 scale web=2
app-0001 scale web=6 app-0002 scale web=4
app-0001 scale web=8 app-0002 scale web=2
app-0001 scale web=10 app-0002 scale web=0
...
app-001 stop
Rollback

A rollback is also quite simple, run up on 0001 and stop on 0002.

80/20 deploy

This would be as simple as running scale web=2 on app-0001, and scale web=8 on app-0002.

Automate Everything

This also reminds me of a similar deploy strategy to capistrano, I might even look at using a similar tool to wrap docker-compose and save a rewrite of the deploy logic.