HTTP 503: Service Unavailable message from SharePoint 2010

I have been upgrading a number of SharePoint 2010 farms to the December 2012 cumulative update. During the install process I have experienced repetitive failures when running the SharePoint 2010 Products Configuration Tool. The tool would advance to some percentage of step 9/10 and then it will just mysteriously fail with no reason given in the dialog box or in the configuration log files. Fortunately recovering from this failure is easy, all you need to do is just re-run the configuration wizard. While I have yet to confirm this, and I'm not sure I can confirm it in any way, I believe this issue might be related to us running SharePoint 2010 on servers that only meet the minimum suggested requirements for memory and processor.

Unfortunately after successfully running the SharePoint 2010 Productions Configuration Wizard and starting Central Administration I was presented with an HTTP Error 503 Service Unavailable. Thinking that this might have just been an issue that affected our Central Administration site I next attempted to browse to a normal site and still got a 503 Service Unavailable message. So I started to scour the internet looking for an answer but couldn't seem to find any reported problems that matched the problems we were having, and there were no signs of a solution that seemed to make sense given the symptoms of our problem. So I began the task of trying to figure out the problem myself.

I started my search at the bottom and opened up the windows service console. Checking the related IIS services they all seemed to be started and running without errors. This lead me to start up the IIS Manager and search for something within it that would suggest it was the cause of these issues. Eventually I was looking at our Application Pools for SharePoint and noticed that the Application Pool for our Central Administration was stopped and in addition a number of other Application Pools related to SharePoint were stopped (You can see this next to #1 in the image below). I started up all of the stopped application pools and then went back and tried the Central Administration site and it was there and working. Just to ensure that this problem did not arise after a reboot I double checked the advanced settings for each Application Pool (#2 below) and ensured that the Start Automatically property was set to true (Pictured below).

The short version of the above for people like me to who hate reading and are just here for the solution:

Received HTTP Error 503 Service Unavailable when accessing SharePoint Central Administration and other sites after a failed execution of the SharePoint 2010 Products Configuration Wizard.

Found the problem was because our SharePoint IIS application pools were not started (1).

Started the application pools and double checked the advanced settings (2) to ensure that the application pool was set to automatically start. 

SharePoint was running fine after the application pools were started and all SharePoint requests were processed successfully.