Automatic failover behavior in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is automatic failover in MongoDB?

Automatic failover is the process where MongoDB automatically switches to a new primary node if the current primary becomes unavailable, ensuring the database stays available without manual intervention.

beginner

What role does a 'primary' node play in MongoDB replica sets?

The primary node receives all write operations and replicates data to secondary nodes. It is the main point for data changes in the replica set.

intermediate

How does MongoDB detect a primary node failure?

MongoDB members send heartbeats to each other. If a majority of nodes do not receive a heartbeat from the primary within a timeout, they consider it down and start an election for a new primary.

intermediate

What is the election process in MongoDB automatic failover?

When the primary fails, eligible secondary nodes hold an election to select a new primary. The node that wins the majority vote becomes the new primary and starts accepting writes.

advanced

Why is a majority vote important in MongoDB failover?

A majority vote prevents split-brain scenarios by ensuring only one primary is elected. This keeps data consistent and avoids conflicts.

What triggers automatic failover in a MongoDB replica set?

A Primary node becomes unreachable

B Secondary node receives a write

C Client disconnects

D Backup completes

Automatic failover happens when the primary node is unreachable or considered down by the replica set members.

During failover, how is the new primary chosen?

A Node with the most data

B Majority vote among eligible secondaries

C Random selection

D Oldest node

Eligible secondary nodes hold an election and the one with majority votes becomes the new primary.

What is the purpose of heartbeat messages in MongoDB replica sets?

A To check node availability

B To backup data

C To transfer data

D To authenticate users

Heartbeat messages help nodes check if other members, especially the primary, are alive and reachable.

What happens if a majority of nodes cannot communicate with the primary?

A Primary remains primary

B Replica set shuts down

C An election is triggered to select a new primary

D All writes are blocked permanently

If the primary is unreachable by a majority, an election is triggered to maintain availability.

Why is it important to have an odd number of voting members in a replica set?

A To reduce storage

B To improve backup speed

C To increase write speed

D To simplify elections and avoid ties

An odd number of voting members helps avoid tie votes during elections, ensuring smooth failover.

Explain how MongoDB handles automatic failover when the primary node fails.

Think about how nodes communicate and decide who becomes the new leader.

Describe why majority voting is critical in MongoDB's automatic failover mechanism.

Consider what could happen if two primaries existed at the same time.