We migrated a core system to our shiny new cluster on Friday. Colin got everything going apart from a call-out to a 3rd party back-end system that uses SOAP.
Tracking down the problem:
The error message was a method_missing talking about load_file.
I did some google work (googling is apparently not allowed by google because it could undermine their copyright - like I care)
It looked like the call to the SOAP client to add the certificates file wasn't working ... however the permissions on the files were correct.
I had a look on Sunday and found that we were missing the Ruby openssl library. This isn't a gem, but part of the standard install. Found this link explaining how to sort it out. Looks like we're missing zlib and some other stuff too.
Interestingly one leg had readline installed and the other didn't, which meant that the console wouldn't work. I couldn't get it to build on the broken leg and resorted to sftp'ing the file from one machine to the other.
This is because you can't get above Ruby 1.8.3 using the apt-get command so you have to build it from source. No idea why it doesn't install standard stuff - there's probably some magic compile switch that isn't documented.
Have fun.