Does both the sql cluster nodes needs to use the same service account ? In my environment I saw one one was using a service account and another was using a local account although the sql agent was using the same acccount and once the failover went to the node which was using the local account i was not able to failback to the original node and also the back up were failing. Is this due to the mismatch of the sql server service account ? please help
All nodes in a cluster should be using the same service account for SQL Server. This is true for both an FCI instance and an Availability Group setup.
For security sake, consider using Group Managed Service Accounts.https://blogs.technet.microsoft.com/askpfeplat/2012/12/16/windows-server-2012-group-managed-service-accounts/
This will allow you to have a service account that will have an strong, automatically changing password for your SQL Servers. Auditors love this. Your risk is minimum since Active Directory is handling the password change and downtime is not required to do this.