Nginx 502 Bad Gateway

This morning I awoke to a 502 Bad Gateway error from Nginx. Luckily it was only one user that made me aware of this! The current setup I'm running is Nginx as a proxy for Apache.

To resolve this, I first checked to see if httpd was running. Surprisingly, httpd was not running. I went ahead and did "service httpd restart" and all was good. 

After fixing the issue, I set out to see why it may not have been running. The issue was caused by the httpd being set to stop at boot time. I fixed this by using "chkconfig httpd on" which set it to start at boot time. Also accomplished with "sudo /sbin/chkconfig --add httpd"

Curly Brackets in Chef/Ruby

Surprise, it helps to know the syntax of the language you are writing in.

The issue I ran into this time has to deal with the curly brackets in Ruby. 

Code Example 1

execute 'policy_selinux' do

  command "semodule -i /tmp/policy.pp"

  action :run

  not_if { 'semodule -l | grep policy' }

end

Code Example 2

execute 'policy_selinux' do

  command "semodule -i /tmp/policy.pp"

  action :run

  not_if 'semodule -l | grep policy' 

end

The key to note between example 1 and 2 is that in the second example there is no use of the curly "{}" brackets. This is for a very good reason. The curly brackets, in our case, are being used like a code block. This means that in example 1, the not_if is evaluating the {'semodule -l | grep policy'} as a code block. The code block evaluates as true all the time because it is evaluating a string that has no arguments to evaluate it(tautology). 

The code example 2 has no "{}" which means that the string is going to be used by the not_if statement. This will not be evaluated as a code block, but a string that is truly a command with a return status. This will allow us to get our return status like we desire.

Below is a good resource that helped lead me to my conclusion.
http://stackoverflow.com/questions/12565/what-do-the-different-brackets-in-ruby-mean