Exam Professional Cloud Database Engineer topic 1 question 96 discussion

The Option D describes the correct answer (even though it is only half part as it doesn't prevent split brain situations but It is better answer than B, A or C), The issue with answer B is It doesn't return to pretest configuration. Same Goes for A as DB-2 still the primary in this case. Option C is not recommended in case region is not available and still you end up having only Primary (DB-1) available and Not Replica (DB-2) we want pre test config which is both DB-1 and DB-2 available. PLEASE UPVOTE SO OTHERS CAN BENEFIT.

https://cloud.google.com/sql/docs/mysql/high-availability#failback

Option D is correct. Option A is false because After a failover, the instance that received the failover continues to be the primary instance, even after the original instance comes back online. After the zone or instance that experienced an outage becomes available again, the original primary instance is destroyed and recreated. Then it becomes the new standby instance. If a failover occurs in the future, the new primary will fail over to the original instance in the original zone. Reference: https://cloud.google.com/sql/docs/mysql/high-availability#failback

Option D is correct. Option A is false because After a failover, the instance that received the failover continues to be the primary instance, even after the original instance comes back online. After the zone or instance that experienced an outage becomes available again, the original primary instance is destroyed and recreated. Then it becomes the new standby instance. If a failover occurs in the future, the new primary will fail over to the original instance in the original zone. Reference: https://cloud.google.com/sql/docs/mysql/high-availability#failback

The Option D describes the correct answer (even though it is only half part as it doesn't prevent split brain situations but It is better answer than B, A or C), The issue with answer B is It doesn't return to pretest configuration. Same Goes for A as DB-2 still the primary in this case. Option C is not recommended in case region is not available and still you end up having only Primary (DB-1) available and Not Replica (DB-2) we want pre test config which is both DB-1 and DB-2 available. PLEASE UPVOTE SO OTHERS CAN BENEFIT.

According to this: https://cloud.google.com/solutions/cloud-sql-mysql-disaster-recovery-complete-failover-fallback#phase_1_setting_up_an_ha_database_instance_for_dr Option D is the correct one. Once you promote a read replica it destroys the old replica flow and you need to create a new instance to promote as primary.

D is correct.

D. If you need to have the primary instance in the zone that had the outage, you can do a failback. A failback performs the same steps as the failover, only in the opposite direction, to reroute traffic back to the original instance. To perform a failback, use the procedure in Initiating failover. https://cloud.google.com/sql/docs/mysql/high-availability#failback

option A- Bring DB-1 back online.

As stated in the documentation (https://cloud.google.com/sql/docs/mysql/replication/cross-region-replicas) the cross region read replica promotion is a manual activity and it destroys all the previous replica flow. The pre-test configuration is having a primary instance on region 1 with 2 read replicas on region 2 and 3; the only way to do that is to create a replica of DB2 in region 1 (DB4), promote it as a primary instance and then create DB4 read replicas on region 2 and 3. - Answer D is the only one in that direction - Answer A is wrong because the replica flow between DB1 and DB2 has been destroyed with the promotion - Answer B is partially correct but not enough - Answer C is wrong because we are talking about read replica, not high availability, and the replica flow between DB1 and DB2 has been destroyed by the promotion

A. Bring back original primary. Tabs at link below shows process for failover and then failback https://cloud.google.com/sql/docs/mysql/high-availability#failback

correct answer is A. Bring DB-1 back online. :)

A you just need to bring it back again as you can see in the Google documentation: https://cloud.google.com/sql/docs/mysql/high-availability#failback

https://cloud.google.com/sql/docs/mysql/replication/cross-region-replicas If the primary instance (db-1) becomes unavailable, you can promote the replica in region B to become the primary. To again have additional replicas in regions A and C, delete the old instances (the former primary instance in A, and the replica in C), and create new read replicas from the new primary instance in B.

A is the correct choice because it allows you to restore the original primary instance. By bringing DB-1 back online, it will automatically synchronize with the promoted replica (DB-2) and resume its role as the primary instance. This ensures that the system returns to the pre-test configuration.

The answer is A. To return to the pre-test configuration, you need to bring DB-1 back online. This will automatically demote DB-2 and make DB-1 the primary instance again. Option B is incorrect because it would re-create DB-1 as a read replica, which is not the pre-test configuration. Option C is incorrect because deleting DB-2 would not automatically revert DB-1 to the primary instance. You would need to manually promote DB-1 to primary. Option D is incorrect because creating DB-4 as a read replica and promoting it to primary would create a new primary instance, but it would not revert DB-1 to its pre-test configuration.

When you promote a read replica to become the new primary instance, the original primary instance (DB-1) is demoted and becomes a replica. To revert to the pre-test configuration, you need to delete the promoted instance (DB-2) so that the original primary instance (DB-1) can automatically resume its role as the primary instance. By deleting DB-2, DB-1 will automatically take over as the primary instance, and the read replicas (DB-3) will continue to replicate data from DB-1.