Sentinel architecture in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Redis Sentinel?

Redis Sentinel is a system that helps monitor Redis servers, automatically switch to a backup if the main server fails, and notify users about the system status.

beginner

What are the main roles of Redis Sentinel?

Redis Sentinel has three main roles: monitoring Redis servers, notifying clients about changes, and performing automatic failover to a backup server if the main one stops working.

intermediate

How does Redis Sentinel decide to failover to a backup server?

Sentinel checks if the main Redis server is down by asking other Sentinels and clients. If enough agree the server is unreachable, Sentinel promotes a backup to be the new main server.

intermediate

What is a quorum in Redis Sentinel?

A quorum is the minimum number of Sentinel instances that must agree a Redis server is down before starting a failover. This prevents mistakes from a single Sentinel's wrong judgment.

beginner

Why is it recommended to run multiple Sentinel instances?

Running multiple Sentinel instances improves reliability by allowing them to vote on server status, reducing false failovers and ensuring the system can handle Sentinel failures.

What is the primary purpose of Redis Sentinel?

A To store data persistently

B To monitor Redis servers and manage automatic failover

C To provide a user interface for Redis

D To backup Redis data to cloud storage

Redis Sentinel monitors Redis servers and automatically switches to a backup if the main server fails.

What does Redis Sentinel use to decide if a master server is down?

A Votes from multiple Sentinel instances

B A single Sentinel's opinion

C Client application logs

D Manual user input

Sentinel requires a quorum of Sentinels to agree a server is down before failover.

What happens during a failover in Redis Sentinel?

A Data is deleted

B Clients disconnect permanently

C All servers restart

D A slave is promoted to master

During failover, Sentinel promotes a slave to become the new master.

Why is it important to have multiple Sentinel instances?

A To avoid false failovers and improve reliability

B To increase data storage capacity

C To speed up Redis queries

D To reduce network traffic

Multiple Sentinels vote to confirm failures, preventing mistakes and improving system reliability.

What is the role of notifications in Redis Sentinel?

A To backup data automatically

B To send emails to users

C To inform clients about server status changes

D To encrypt Redis data

Sentinel notifies clients when the master changes or other important events happen.

Explain how Redis Sentinel monitors and manages failover in a Redis setup.

Think about how Sentinel watches servers and what it does when the main server stops working.

Describe why running multiple Sentinel instances is important and how they work together.

Consider how decisions are made and why one Sentinel alone is not enough.