Sentinel configuration in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Sentinel monitoring configuration output

Given the following Redis Sentinel configuration snippet, what will be the output of the SENTINEL masters command?

sentinel monitor mymaster 192.168.1.100 6379 2
sentinel down-after-milliseconds mymaster 5000
sentinel failover-timeout mymaster 60000
sentinel parallel-syncs mymaster 1

A []

B [{"name":"mymaster","ip":"127.0.0.1","port":6379,"quorum":2}]

C [{"name":"mymaster","ip":"192.168.1.100","port":6380,"quorum":2}]

D [{"name":"mymaster","ip":"192.168.1.100","port":6379,"quorum":2}]

💡 Hint

Check the IP and port values in the sentinel monitor command.

The SENTINEL masters command returns the list of monitored masters with their configured IP, port, and quorum. The configuration sets the master IP to 192.168.1.100 and port 6379 with quorum 2.

🧠 Conceptual

intermediate

Understanding Sentinel quorum

In Redis Sentinel configuration, what does the quorum number specify?

A The number of seconds before a master is considered down

B The number of replicas to promote during failover

C The number of Sentinels that must agree a master is down before failover starts

D The number of clients allowed to connect to the master

💡 Hint

Think about how Sentinels decide to start failover.

Quorum is the count of Sentinels that must agree the master is unreachable before failover begins.

📝 Syntax

advanced

Identify the syntax error in Sentinel config

Which of the following Sentinel configuration lines contains a syntax error?

A sentinel monitor mymaster 192.168.1.100 6379 2

B sentinel parallel-syncs mymaster

C sentinel failover-timeout mymaster 60000

D sentinel down-after-milliseconds mymaster 5000

💡 Hint

Check if all required parameters are present.

The 'sentinel parallel-syncs' command requires the master name and the number of replicas to sync in parallel. Option B is missing the number parameter.

❓ optimization

advanced

Optimizing Sentinel failover timeout

You want to reduce the failover time in your Redis Sentinel setup. Which configuration change will most directly reduce the failover duration?

A Decrease the value of sentinel failover-timeout

B Increase the value of sentinel down-after-milliseconds

C Increase the quorum number

D Decrease the number of Sentinels monitoring the master

💡 Hint

Failover-timeout controls the maximum time for failover to complete.

Lowering failover-timeout reduces the maximum time Sentinel waits before completing failover.

🔧 Debug

expert

Debugging Sentinel failover not triggering

You have 3 Sentinels monitoring a master with quorum set to 2. The master goes down, but failover does not start. Which is the most likely cause?

A Only one Sentinel detected the master as down, so quorum was not reached

B The failover-timeout is set too low

C The master IP address is incorrect in the Sentinel config

D The parallel-syncs value is set to zero

💡 Hint

Quorum requires multiple Sentinels to agree on master status.

Failover requires at least quorum number of Sentinels to agree the master is down. If only one Sentinel detects it, failover won't start.