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In addition to the SharePoint patching installation guide that was published by me few days back, I’ve come up with a new article that gives a detailed description about what a Cumulative Update is all about and the things you need to know about a CU.
What is a CU?
A CU (i.e. Cumulative Update) is a software package that includes fixes for problems with Microsoft products that have been reported by customers to Microsoft support in the form of support cases.
What is included?
As the name says, the updates/fixes that are included in the package are always Cumulative (meaning, it includes all the new and all previously released fixes (CUs and PUs) since the release of the oldest supported service pack.
How often does Microsoft release SharePoint Cumulative Updates?
Microsoft releases Cumulative Updates (CUs) once in every month.
How does Microsoft test Cumulative Updates before deployment?
All Cumulative Updates are tested extensively before each public release. If an issue, such as a regression, is discovered on a CU that could potentially impact the application, the CU will be cancelled and will be rescheduled to a later CU.
Are CU’s Multilingual?
Yes. The CU package includes fixes for all the languages. So, no matter what language you download the CU package in, the fixes/updates in the package will remain the same.
What is the prerequisite?
The oldest supported service pack. For instance, all the SharePoint CUs post the SP1 release and need the SP1 to be installed for SP 2013. In the case of SP 2010, all the CU’s that were released post SP2 need SP2 to be installed first after which you can install those CUs .
When to install?
CUs should only be installed to resolve specific issues fixed with the CUs as mentioned in each CU KB article: "Apply this hotfix only to systems that are experiencing the problems described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.” Or if advised to install by Microsoft Support.
Impact on future fixes
In general, a CU is not a prerequisite of future CUs and PUs. However, this may not be the case always. There have been a few scenarios where a CU that was released a few months back, tends to become a prerequisite for the later CUs. So, before installing any CU, please take a look at the related KB article and make sure you have all the necessary prerequisites in place.
Installation Sequence
Installing the CU doesn’t require any specific order, you can do it on any server in the farm and then go on by installing it on other Servers in the Farm (meaning that you can do it on the WFE Server first and then on the APP server). Although it’s OK to go ahead and install the CU in any order on the Server. Based on my experience with installing the CU, I would suggest you to do it on the WFE Server first.
Ensure that the WFE is taken out of the Load balancer pool so that it’s not serving user traffic and then go ahead and install the CU and reboot the server. Once the server comes back online, verify whether all the components have been installed correctly under Control Panel and the Central administration site is accessible. This is just to ensure that the installed CU didn’t do any harm to the server.
It’s ok to lose a WFE but not an APP Server. I hope you’re getting the idea here. Also, if by any chance if you’re patching the Farm during business hours (which might ideally not be the case unless it’s a TEST /UAT farm), then make sure that the Server on which you’re installing the CU, is taken out of the load balancer, so that the user traffic doesn’t goes to that Server. So, the idea to keep in mind is, do it on the WFE Servers first and then on the APP Server.
Running the SharePoint Configuration Wizard
Unlike the CU installation, you can’t run the “SharePoint Configuration Wizard” in any order. It must be running on the Server which is hosting the “Central Administration” site first and then on the WFE and APP Servers.
It’s a 6-step process which might take an hour at the max (in an ideal scenario) to run and complete. Once it’s completed successfully on the Server where CA is hosted, please try opening the CA site and make sure that everything looks fine and make sure you’re able to access the SharePoint sites.
By any chance, if the CA site is not coming up, please stop right there and fix it. Without fixing the CA site issue, don’t proceed further with running the Configuration Wizard on the other Servers. This is the basic rule of thumb to be followed while patching a SharePoint Farm. You need to follow the same procedure for all the Servers in the Farm.