Attempting to re-install postgres fails due to rabbitmq

Question

On 12.04, when I do apt-get install on postgresql (which is already installed), it returns an error that mentions rabbitmq-server. What are the circumstances that could cause this type of failure?

# apt-get install -y postgresql
Reading package lists... Done
Building dependency tree       
Reading state information... Done
postgresql is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 80 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up rabbitmq-server (2.7.1-0ubuntu4) ...
Starting rabbitmq-server: FAILED - check /var/log/rabbitmq/startup_{log, _err}
rabbitmq-server.
invoke-rc.d: initscript rabbitmq-server, action "start" failed.
dpkg: error processing rabbitmq-server (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 rabbitmq-server
E: Sub-process /usr/bin/dpkg returned an error code (1)

Answer 1

It turns out that rabbitmq-server could not start up because it couldn't resolve the hostname, so adding the appropriate line to /etc/hosts fixed it:

127.0.1.1 hostname.example.com hostname

I'm still not exactly sure what triggers the rabbit service start command after postgres installs.