SQL Server 2014 SP2 upgrade on Alwayson + FCI I want to upgrade my SQL Server 2014 to SP2 which is involved in SQL Server FCI and Alwayson. Below is my environment details:

    Nodes: SERVER-A, SERVER-B, SERVER-C, SERVER-D
    SQL Server clustered instances : Instance-A, Instance-B, Instance-C
    SQL Server edition and version : SQL Server 2014 EE SP1 on all 3 clustered instances
    Windows server edition and version : Windows server 2012 R2 STD



SQL Server clustered Instance-A runs on SERVER-A and is installed
between SERVER-A and SERVER-B. 
SQL Server clustered Instance-B runs on SERVER-B and is installed
between SERVER-A and SERVER-B.
SQL Server clustered Instance-C runs on SERVER-C and is installed
    between SERVER-C and SERVER-D.
SQL Server clustered Instance-A has Alwayson configured for some DBs between Instance-A and Instance-C. Instance-A acts as Primary replica and clustered Instance-C acts as its secondary replica. Alwayson failover mode for DBs is manual.


Please let me know how should I go about patching both my SQL Server clustered instances and any precautions to be taken.
The answer can be found here: https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/upgrading-always-on-availability-group-replica-instances
I've used this method several times on 2 and 3 node AlwaysOn Availability Group implementations, and it works very well, and is explained in great detail in the above link.