Support load-balance proxy groups?

[bedroge]

The current setup only allows you to specify proxy groups with one entry per group, by using semicolon separated entries for the proxy list. By using pipes, you can also define multiple proxies per group; this will then act as a load-balance group, see:
https://cvmfs.readthedocs.io/en/2.2/cpt-configure.html#proxy-lists
Do we want/need this? Only seems to make sense if you have more than two proxies per site, e.g. two clusters with two proxies per cluster.

[boegel]

This could be interesting for large sites with lots of different systems, I guess...

I can imagine that we would set up a proxy per cluster for example, but I haven't checked with our sysadmins.

For now, a single proxy is probably fine, certainly for the pilot.

The Ansible stuff is useful (both to make it easy and as "reference implementation"), but I doubt we would use this for a production setup, we would integrate the CVMFS configuration in our own system (which uses Quattor).

[rptaylor]

The 2.2 documentation is old, there are some more examples in the latest version explaining the difference between semicolon and pipe: https://cvmfs.readthedocs.io/en/latest/cpt-configure.html#proxy-list-examples