General questions about SQL Server

Hi.  Thanks in advance.

I've soft of been put in a position where I'm expected to do DBA type tasks but I don't have a lot of experience with being a SQL DBA.  I'm learning (PluralSight courses, reading, sample DBs, etc) but this is going slow.  So thanks in advance for helping me out.

1. In a high availability configuration, can a SQL secondary server be rooted at any time without consequences to the Primary?
2. In a high availability configuration, if I go onto a the secondary SQL server and find that databases in the HA database "Availability Databases" folder show a yellow exclamation, but no errors are showing in the SQL Server error log. Can I safely re-add the database (on secondary) to HA via ALTER AVAILABILITY GROUP [HA GROUP NAME] ADD DATABASE [DB NAME](TDE is enabled).  On the primary, the database shows "Synchronizing"
3. In #3 above, I just found the cluster showed the following error:

The failover cluster showed the following errors:

The cluster service has determined that this node does not have the latest copy of cluster configuration data. Therefore, the cluster service has prevented itself from starting on this node.

Try starting the cluster service on all nodes in the cluster. If the cluster service can be started on other nodes with the latest copy of the cluster configuration data, this node will be able to subsequently join the started cluster successfully.

If there are no nodes available with the latest copy of the cluster configuration data, please consult the documentation for 'Force Cluster Start' in the failover cluster manager snapin, or the 'forcequorum' startup option. Note that this action of forcing quorum should be considered a last resort, since some cluster configuration changes may well be lost.

• Would this be the cause of the HA issues, correct (or no?)
• How does this sort of thing happen?
• In the error above, where exactly is the cluster configuration?

4.  What are the implications of restarting a failover cluster?  Are there tasks I should perform first?  Is something likely to break during a restart?

5.  What would cause a database to show a yellow exclamation mark in HA "Availability Databases" folder?  No one has been messing with it in SSMS.  The SQL Server logs show no errors, only "informational" entries.

Thanks.

LoganT.