Deploying new versions of an image instantly - docker

Question

I would like to have 3 versions of my container running at any one time (on the same machine). Something like this:
version v7 (stage)
version v6 (live)
version v5 (old)
then I would like to map this to 3 urls:
v7.example.com
v6.example.com
v5.example.com
And also, a 4th url, which refers to the current (or default) version:
www.example.com (which maps to http://v6.mydomain.com)
Presumably, I could take some configuration step that would change the "default" version from v6 to v7. That step should hopefully be instant and atomic.
The idea is that deploying the next version of an app is a distinct step from activating that version (by activate, I mean making that version the default).
Therefore a rollout (or a rollback) would simply be a matter of changing the default version to the next (or previous) version.
Google App Engine supports this kind of pattern and I really like it.
Has anyone set something like this up using Docker? I would appreciate any advice on how to do it. Thanks.

Answer 1

I would do this with a reverse proxy in front of the containers running your webapp.
Example using the jwilder/nginx-proxy image
Let's say your docker host IP address is 11.22.33.44.
Let's say your docker images are:
mywebapp:5 for v5
mywebapp:6 for v6
mywebapp:7 for v7
First, make sure your DNS is set up so that v5.example.com, v6.example.com, v7.example.com and www.example.com all resolve to 11.22.33.44.
Start a jwilder/nginx-proxy on your docker host:
docker run -d --name reverseproxy -p 80:80 -v /var/run/docker.sock:/tmp/docker.sock:ro -e DEFAULT_HOST=www.example.com jwilder/nginx-proxy
Set v6 as the default one
Start the webapps containers:
docker run -d -name webapp5 -e VIRTUAL_HOST="v5.example.com" mywebapp:5
docker run -d -name webapp6 -e VIRTUAL_HOST="v6.example.com,www.example.com" mywebapp:6
docker run -d -name webapp7 -e VIRTUAL_HOST="v7.example.com" mywebapp:7
The jwilder/nginx-proxy will use the value of the VIRTUAL_HOST environment variable to update its configuration and route the requests to the correct container.
How to make v7 the new default one
First, remove container webapp7 and create a new one with www.example.com added to the VIRTUAL_HOST variable:
docker rm webapp7
docker run -d -name webapp7 -e VIRTUAL_HOST="v7.example.com,www.example.com" mywebapp:7
In this state, the reverse proxy will load balance queries for www.example.com to both webapp6 and webapp7 containers.
Finally, remove container webapp6 and eventually recreate it, but without www.example.com in the VIRTUAL_HOST value:
docker rm webapp6
docker run -d -name webapp6 -e VIRTUAL_HOST="v6.example.com" mywebapp:7

Answer 2

I thought I would share what I ended up doing. I took Thomasleveil's advice to use nginx. But rather than starting and stopping a whole docker container and nginx just to switch versions, I do this:
Change the port number in the nginx config file (see file below)
Call service nginx reload (which is instant).
server{
location / {
proxy_pass http://192.168.1.50:81/;
}
}