I have two Centos 6 test servers: master and one slave.
The slave is added to Webmin Servers Index without problems (I checked the status).
I added both to the Cluster Software Packages module.
When I try to install the package "nc" from YUM on all hosts (ie, those two) the output is:
Failed to install on this server : An error occurred installing the specified updates Failed to install on 192.168.1.67 : An error occurred installing the specified updates
The first failure is seen immediately and then the output stalls forever. If we login via ssh on the other host and kill the rpc.cgi processes the second message appears.
On the master machine "this server" we see these messages on the logs:
"POST /cluster-software/install_pack.cgi?id=13429162297900 HTTP/1.1" 200 3143
On the slave machine we see messages such as this one:
"POST /rpc.cgi HTTP/1.0" 200 44
No package gets installed on either machine.
yum install nc
from the shell works correctly.