Implementing improved error handling and error cleanup.

In version 2.9.8.19 new error handling was implemented to improve the clean up experience during migration failures and increase the reliability of migrations.

The first improvement involves implementing error handling in the function that moves on-premises groups between organizational units. The move command is called up to three times in the module. The first call moves the group from the OU that it is currently into the non-sync OU specified in the migration command. It was possible in the original code that if an exception occurred on moving the group to the non-sync OU this would not cause the migration to fail. This in turn created an endless loop in the migration process scanning for the distribution list deletion in Office 365. The migration would neither succeed nor fail. The current code now attempts the move to the non-sync OU and if an exception occurs will retry the operation up to 5 times waiting 5 seconds between each attempt. If the move is not successful in 5 tries the migration is halted. The second call involves moving the group from the non-sync OU back to the sync OU. The code now attempts this operation 1 time and if the move fails a post create error is created alerting the administrator that manual movement is required. Failing this move was an optional task. The last potential call for a move occurs when the migration fails. If the migration fails after moving the group to a non-sync OU the group will remain there until the administrator move the group back to the sync OU. If the migration fails a single attempt at moving the group back to the original OU is performed. If an error is encountered the migration will end as a result of the previous failure.

The second improvement provides some clean up capabilities in response to failure. There are two scenarios that potentially require cleanup after a failed migration. The first scenario is the temporary distribution group created in Office 365. In order to speed operations and limit downtime that the group is unavailable in the cloud operations that potentially take a significant amount of time are performed on a temporary distribution list created in Office 365 as a part of the migration. In previous versions if a failure was encountered after this temporary distribution list was created but before it was renamed as part of migration the group would often be orphaned if a failure occurs. New logic is now implemented that tracks the migration status and if the migration fails between the creation of the temporary distribution list and the renaming / finalizing operation of the migration the temporary distribution list is automatically cleaned up. The second scenario is that failed migrations prior to disabling the distribution list on premises often resulted in the distribution list remaining in the non-sync OU. New is now implemented that tracks the migration status and if a failure occurs prior to disabling the on-premises distribution list an attempt is made to move the list back to the original OU. This should allow the synchronization process to detect the original distribution list and provision the recipient again in the cloud limiting the likelihood of an extended outage pending administrator intervention. It is important to note that the module does not trigger a synchronization in response to this event but rather waits for the current sync cycle to run. If your sync cycles are not default the outage in the cloud may be longer than anticipated.

These changes should hopefully improve the reliability of the migrations and prevent manual cleanup.