Explicitly passing a serverID in copydb config means only one copydb isntance can operate on a source mysql server at a time. This would be probably okay in a production environment, but for parallel testing where you have multiple copydb instance opearing on the same source mysql server can create an issue.
It's better to not explicitly pass a serverID from copydb and let the binlog_streamer generate a random serverID.
Explicitly passing a serverID in copydb config means only one copydb isntance can operate on a source mysql server at a time. This would be probably okay in a production environment, but for parallel testing where you have multiple copydb instance opearing on the same source mysql server can create an issue.
It's better to not explicitly pass a serverID from copydb and let the binlog_streamer generate a random serverID.