Master-replica architecture in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of the command INFO replication on a Redis replica?

You run INFO replication on a Redis replica node. What key information will you see in the output?

Redis

INFO replication

A role:replica, master_host:<ip>, master_link_status:up

B role:master, connected_slaves:0

C role:client, connected_clients:10

D role:sentinel, monitored_masters:1

💡 Hint

Think about what role a replica plays and what info it reports about its master.

A Redis replica reports its role as 'replica' (or 'slave' in older versions), shows the master's IP, and the link status to the master. Masters report connected slaves, sentinels report monitored masters, and clients report connected clients.

🧠 Conceptual

intermediate

Why does a Redis replica not accept write commands by default?

In a master-replica setup, why are write commands disabled on replicas by default?

A To prevent data inconsistency by ensuring writes happen only on the master

B Because replicas have no memory to store data

C To reduce network traffic between nodes

D Because replicas only store metadata, not actual data

💡 Hint

Consider the role of master and replica in data consistency.

Writes are allowed only on the master to keep data consistent. Replicas replicate data from the master and do not accept writes to avoid conflicts.

📝 Syntax

advanced

Which Redis command correctly promotes a replica to master?

You want to promote a Redis replica to become a master. Which command will do this correctly?

A PROMOTE MASTER

B SLAVEOF NO ONE

C REPLICAOF NO ONE

D MASTER PROMOTE

💡 Hint

The command changed name in recent Redis versions.

The command to promote a replica to master is 'REPLICAOF NO ONE' in modern Redis versions. 'SLAVEOF' is deprecated but still works in older versions. The other commands do not exist.

❓ optimization

advanced

How can you reduce replication lag in a Redis master-replica setup?

Which approach helps reduce replication lag between master and replica in Redis?

A Use synchronous replication mode

B Increase the number of replicas to distribute load

C Disable AOF persistence on the master

D Enable diskless replication to send data directly over the network

💡 Hint

Think about how data is transferred from master to replica.

Diskless replication sends data directly over the network without writing to disk first, reducing lag. Increasing replicas doesn't reduce lag per replica. Disabling AOF affects persistence, not replication lag. Redis replication is asynchronous; synchronous mode is not supported.

🔧 Debug

expert

Why does a Redis replica show master_link_status:down after network recovery?

After a network outage, your Redis replica shows master_link_status:down even though the network is restored. What is the most likely cause?

A The master has crashed and is not accepting connections

B The replica's replication backlog is lost and needs a full resync

C The replica is still configured as a master

D The replica's IP address changed and is not updated

💡 Hint

Consider what happens to replication state after network failures.

If the replication backlog is lost during outage, the replica cannot catch up incrementally and must perform a full resync, causing the link to stay down until resync completes. Master crash or IP change would cause different symptoms. Replica configured as master would not show master link status.