Previous versions of MongoDB connector used hard coded secondaryPreferred read preference. This will change in 2.4 and debezium will always honor read preference set via connection string.

This is a breaking change since the MongoDB default read preference is primary.
Keeping the original behaviour would be confusing as it was different form MongoDB's default. Nevertheless the change is acceptable as the behaviour can be easily configured to that of previous version by adding the following to the connection string.

&readPreference=secondaryPreferred

Additionally to make this configurable also for sharded cluster with mongodb.connection.mode=replica_set a new property mongodb.connection.string.shard.params was introduced