Sentinel quorum concept in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Sentinel quorum in Redis Sentinel?

The Sentinel quorum is the minimum number of Sentinel instances that must agree a master is down before a failover is triggered.

beginner

Why does Redis Sentinel require a quorum before starting a failover?

To avoid false failovers caused by network glitches or temporary issues, ensuring that enough Sentinels agree the master is really down.

intermediate

How do you configure the quorum in Redis Sentinel?

You set the quorum number in the Sentinel configuration file using the 'sentinel monitor' command, for example: sentinel monitor mymaster 127.0.0.1 6379 2 (where 2 is the quorum).

beginner

What happens if the quorum is not reached in Redis Sentinel?

If the quorum is not reached, Sentinel will not start a failover, and the master will continue to be considered up.

intermediate

How does Sentinel quorum relate to high availability?

Quorum helps ensure that failover decisions are reliable, which is key for maintaining high availability and avoiding split-brain scenarios.

What does the Sentinel quorum represent in Redis Sentinel?

A The minimum number of Sentinels that must agree the master is down

B The number of slaves connected to the master

C The number of clients connected to Redis

D The maximum number of failovers allowed

The quorum is the minimum number of Sentinel instances that must agree the master is down before failover.

If the quorum is set to 3, how many Sentinels must agree the master is down to trigger failover?

A 1

B 2

C 3

D 4

The quorum number defines how many Sentinels must agree; if set to 3, at least 3 must agree.

What is the risk of setting the Sentinel quorum too low?

A Failover may never happen

B False failovers due to temporary network issues

C Slower failover process

D More memory usage

A low quorum can cause failover to trigger incorrectly during brief network glitches.

Where do you configure the Sentinel quorum value?

A In the Sentinel configuration file

B In the Redis server config file

C In the client application

D In the operating system settings

The quorum is set in the Sentinel configuration file using the 'sentinel monitor' command.

What happens if the quorum is not reached when a master is suspected down?

A Sentinel promotes a slave anyway

B Sentinel immediately triggers failover

C Sentinel shuts down

D Sentinel ignores the master status and continues monitoring

Without quorum agreement, Sentinel does not trigger failover and keeps monitoring.

Explain the role of quorum in Redis Sentinel failover process.

Think about how Sentinels decide together before acting.

Describe how to set and why to choose a proper quorum value in Redis Sentinel.

Consider the trade-off between quick failover and avoiding mistakes.