The recent release of Cloud Manager has changed the way we add new members to a replica set with Automation. Here’s how we’ve changed it, and why.
Previously, if you asked Cloud Manager to add a replica set member for you with a particular vote and priority setting, we would simply add a new member with that priority and vote setting. Now we do something a little different, and a little safer.
With this release, we save the vote and priority settings, but we don’t set them immediately. Instead, we start with vote and priority set to 0 until the initial sync has completed. One benefit of this procedure is that it means that any write concern you use will not be affected by the new node until it is ready to receive replicated writes. Another reason is to prevent the node in initial sync from vetoing a legitimate election. Once the initial sync is complete, we set the priority and votes to the desired levels.