Master-replica architecture in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a Redis instance as a replica of a master.

Redis

replicaof [1] [2]

Drag options to blanks, or click blank then click option'

A192.168.1.100 6380

B127.0.0.1 6379

Clocalhost 6379

Dmaster 6379

Attempts:

3 left

💡 Hint

Common Mistakes

Using an incorrect hostname or port.

Omitting the port number.

The replicaof command requires the master host and port. Here, localhost 6379 correctly points to the master Redis instance.

2fill in blank

medium

Complete the command to check the role of a Redis instance.

Redis

info replication | grep [1]

Drag options to blanks, or click blank then click option'

Astatus

Bmaster

Creplica

Drole

Attempts:

3 left

💡 Hint

Common Mistakes

Using master or replica directly instead of the key.

Using unrelated keys like status.

The info replication command shows replication info. Filtering by role shows if the instance is master or replica.

3fill in blank

hard

Fix the error in the command to promote a replica to master.

Redis

redis-cli [1]

Drag options to blanks, or click blank then click option'

Areplicaof noone

Breplicaof no one

Creplicaof none

Dreplicaof no_one

Attempts:

3 left

💡 Hint

Common Mistakes

Writing 'noone' as one word.

Using 'none' or 'no_one' which are invalid.

The correct command to promote a replica to master is replicaof no one with a space between 'no' and 'one'.

4fill in blank

hard

Fill both blanks to configure a replica to follow a master at IP 10.0.0.5 and port 6380.

Redis

replicaof [1] [2]

Drag options to blanks, or click blank then click option'

A10.0.0.5

B6380

C6379

Dlocalhost

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping IP and port positions.

Using default port 6379 instead of 6380.

The replicaof command needs the master's IP and port. Here, the IP is 10.0.0.5 and the port is 6380.

5fill in blank

hard

Fill all three blanks to create a Redis configuration snippet that sets a replica to follow master at 192.168.0.10 port 6379 and disables replica read-only mode.

Redis

replicaof [1] [2]
replica-read-only [3]

Drag options to blanks, or click blank then click option'

A192.168.0.10

B6379

Cno

Dyes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'yes' for replica-read-only which keeps replica read-only.

Mixing up IP and port order.

The replicaof command sets the master IP and port. Setting replica-read-only no allows writes on the replica.

Practice

1. What is the main purpose of the master-replica architecture in Redis?

easy

A. To copy data from one main server to others for safety and speed

B. To delete data from all servers simultaneously

C. To run multiple unrelated databases on one server

D. To encrypt data on the master server only

Solution

1. Step 1: Understand the role of master and replicas

   The master server holds the original data, and replicas copy this data to keep backups and improve read speed.

2. Step 2: Identify the main goal of this setup

   This setup is mainly for safety (backup) and speed (load distribution).

3. Final Answer:

   To copy data from one main server to others for safety and speed -> Option A

4. Quick Check:

   Master-replica = data copy for safety and speed [OK]

Hint: Master copies data to replicas for safety and speed [OK]

Common Mistakes:

• Thinking replicas delete data
• Confusing master-replica with encryption
• Believing replicas run unrelated databases

2. Which Redis command correctly sets a server as a replica of another?

easy

A. REPLICAOF <port>

B. SETREPLICA <port>

C. SLAVEOF <port>

D. COPYTO <port>

Solution

1. Step 1: Recall the Redis command for setting a replica

   The correct command is SLAVEOF followed by the master's IP and port.

2. Step 2: Check the options for exact command syntax

   Only SLAVEOF <port> uses the correct command SLAVEOF.

3. Final Answer:

   SLAVEOF <master-ip> <port> -> Option C

4. Quick Check:

   Set replica with SLAVEOF command [OK]

Hint: Use SLAVEOF to set replica, not REPLICAOF or others [OK]

Common Mistakes:

• Using REPLICAOF instead of SLAVEOF
• Trying non-existent commands like SETREPLICA
• Confusing COPYTO with replication commands

3. Given this Redis command sequence on a replica server:

SLAVEOF 192.168.1.10 6379
GET user:100

What will happen if the master at 192.168.1.10 is down?

medium

A. The replica will return an error because it can't reach the master

B. The replica will return the last synced value for user:100

C. The replica will become master automatically

D. The replica will delete the user:100 key

Solution

1. Step 1: Understand replica behavior when master is down

   The replica keeps the last synced data even if the master is offline.

2. Step 2: Predict the GET command result on replica

   GET will return the last known value for the key from the replica's local data.

3. Final Answer:

   The replica will return the last synced value for user:100 -> Option B

4. Quick Check:

   Replica serves last synced data if master is down [OK]

Hint: Replica serves cached data if master is unreachable [OK]

Common Mistakes:

• Assuming replica errors out when master is down
• Thinking replica auto-promotes to master
• Believing replica deletes keys on master failure

4. You run SLAVEOF NO ONE on a Redis replica server but it still behaves like a replica. What is the likely problem?

medium

A. The server is still connected to the master and did not switch roles

B. The server needs a restart to apply the change

C. The command was typed incorrectly; it should be SLAVE OF NO ONE

D. SLAVEOF NO ONE only works on master servers

Solution

1. Step 1: Understand what SLAVEOF NO ONE does

   This command tells the server to stop replicating and become a master.

2. Step 2: Identify why the server still acts as replica

   If the server is still connected or replication not stopped properly, it remains a replica.

3. Final Answer:

   The server is still connected to the master and did not switch roles -> Option A

4. Quick Check:

   Server must disconnect from master to become master [OK]

Hint: Ensure replica disconnects from master to become master [OK]

Common Mistakes:

• Typing SLAVE OF instead of SLAVEOF
• Thinking restart is always needed
• Believing SLAVEOF NO ONE only works on masters

5. You want to ensure your Redis setup continues working if the master fails. Which approach best uses master-replica architecture?

hard

A. Use only one replica and manually copy data to it daily

B. Disable replication and rely on backups only

C. Run multiple masters without replicas to balance load

D. Set multiple replicas and configure automatic failover to promote a replica to master

Solution

1. Step 1: Identify the goal of continuous operation

   To keep Redis working if master fails, replicas must be ready to take over automatically.

2. Step 2: Evaluate options for failover and replication

   Set multiple replicas and configure automatic failover to promote a replica to master uses multiple replicas and automatic failover, which is the best practice.

3. Final Answer:

   Set multiple replicas and configure automatic failover to promote a replica to master -> Option D

4. Quick Check:

   Multiple replicas + auto failover = high availability [OK]

Hint: Use multiple replicas with auto failover for master failure [OK]

Common Mistakes:

• Relying on manual data copy only
• Running multiple masters without replicas
• Disabling replication and trusting backups alone