Automatic failover behavior in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What triggers automatic failover in MongoDB replica sets?

In a MongoDB replica set, what event causes the automatic failover process to start?

A When a secondary node finishes syncing data

B When the primary node becomes unreachable or stops responding

C When a client disconnects from the database

D When the replica set configuration is changed manually

💡 Hint

Think about what happens if the main server stops working.

Automatic failover starts when the primary node is unreachable or stops responding, so a new primary can be elected to keep the database available.

❓ query_result

intermediate

Result of election after primary failure

Given a MongoDB replica set with 3 members: one primary and two secondaries, if the primary goes down, what will be the state of the replica set after automatic failover?

A The replica set becomes unavailable until manual intervention

B All members become secondary

C The original primary remains primary despite being down

D One of the secondaries becomes the new primary, and the other remains secondary

💡 Hint

Think about how MongoDB keeps the database available after failure.

When the primary fails, one of the secondaries is elected as the new primary to maintain availability.

📝 Syntax

advanced

Identify the correct command to check replica set status

Which MongoDB shell command correctly shows the current status of the replica set, including primary and secondaries?

A show replSet

B db.replicaSetStatus()

C rs.status()

D rs.showStatus()

💡 Hint

It is a method of the rs object.

The rs.status() command returns detailed information about the replica set's current state.

❓ optimization

advanced

Optimizing failover time in MongoDB replica sets

Which configuration change can reduce the time it takes for automatic failover to complete in a MongoDB replica set?

A Decrease the electionTimeoutMillis setting

B Disable write concern majority

C Increase the heartbeatIntervalMillis setting

D Increase the priority of secondary nodes to zero

💡 Hint

Failover speed depends on how quickly nodes detect primary failure.

Lowering electionTimeoutMillis makes secondaries detect primary failure faster, triggering quicker elections.

🔧 Debug

expert

Diagnosing failover failure in MongoDB replica set

A MongoDB replica set does not perform automatic failover when the primary node goes down. Which of the following is the most likely cause?

A The majority of voting members are not available to elect a new primary

B The replica set has more than 3 members

C The heartbeatIntervalMillis is set too low

D The primary node has a higher priority than secondaries

💡 Hint

Think about what is needed for an election to succeed.

Failover requires a majority of voting members to be available to elect a new primary. If the majority is not reachable, failover cannot occur.