Improve OpenStack's documentation on RabbitMQ as needed

[michaelklishin]

Filing it here for the lack of a more suitable place.

We need to review OpenStack's documentation on RabbitMQ setup and maintenance, and contribute improvements as we see fit.

[michaelklishin]

(Hopefully still) relevant guides:

• http://docs.openstack.org/high-availability-guide/content/ha-aa-rabbitmq.html
• http://docs.openstack.org/juno/install-guide/install/apt/content/ch_basic_environment.html
• http://docs.openstack.org/juno/install-guide/install/apt/content/neutron-network-node.html
• http://docs.openstack.org/juno/install-guide/install/apt/content/ch_nova.html
• http://docs.openstack.org/high-availability-guide/content/s-rabbitmq.html

[michaelklishin]

Some specific points of improvement:

• Mention RAM and disk limits, in particular what values are dangerous (and where defaults don't fit production needs)
• Recommend Erlang 17.x
• They suggest using the guest user. It really should be a separate user, e.g. named "openstack", as "guest" is limited to localhost connections in recent releases.
• We should recommend using "autoheal" for partition handling.
• Recommend an odd number of nodes

[michaelklishin]

Started a thread about his on openstack-docs. This means at least one addition to the above points: our own guide dedicated to OpenStack, similar to the one on EC2.

We need to collect a list of topics it should cover.

[michaelklishin]

This section should recommend using our apt repositories as opposed to relying on Ubuntu/Debian ones, which are at least 6 months behind.

[michaelklishin]

This section also mentions rabbitmq-plugins, which doesn't seem to be a valid package for either Debian or Ubuntu.

[michaelklishin]

This section should briefly mention what the cookie is. It currently leaves out the fact that the cookie can be anything, suggesting the user copies it from the first node after starting it. Can be clarified.

[michaelklishin]

This guide should mention partition handling strategies and link to our related guides.

[michaelklishin]

The above guide could mention automatic clustering and again, link to our docs.

[michaelklishin]

This guide mentions that RabbitMQ has to be restarted to enable queue mirroring. I'd say we should consider mentioning policies.

[michaelklishin]

Active/Passive (DRBD) guide also mentions the cookie.

[michaelklishin]

I believe this is no longer as relevant as it was in spring 2015. Documentation improvements never end and evolve with deployment strategies, so I think this should be closed now.