Replication configuration in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Redis

replicaof [1] [2]

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

A192.168.1.100 6379

Blocalhost 6380

C127.0.0.1 6379

D0.0.0.0 7000

Attempts:

3 left

💡 Hint

Common Mistakes

Using localhost instead of the actual master IP.

Using the wrong port number.

The replicaof command requires the IP address and port of the master server. Here, 192.168.1.100 6379 is the correct master address and port.

2fill in blank

medium

Complete the Redis configuration line to enable replication in the config file.

Redis

replicaof [1] [2]

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

Amasterhost 6379

B192.168.0.10 6379

C0.0.0.0 7000

Dlocalhost 6380

Attempts:

3 left

💡 Hint

Common Mistakes

Using placeholder words like 'masterhost' instead of an IP.

Using incorrect port numbers.

In the Redis config file, replicaof is followed by the master's IP and port. The correct master IP here is 192.168.0.10 and port 6379.

3fill in blank

hard

Fix the error in the command to configure a Redis replica.

Redis

replicaof [1]

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

A192.168.1.50

Blocalhost 6379

C192.168.1.50 6379

D127.0.0.1 7000

Attempts:

3 left

💡 Hint

Common Mistakes

Providing only the IP without the port.

Using wrong port numbers.

The replicaof command requires both the IP address and the port number separated by a space. Option C correctly provides both.

4fill in blank

hard

Fill both blanks to configure a Redis replica with the correct master IP and port.

Redis

replicaof [1] [2]

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

A10.0.0.5

Blocalhost

C6379

D7000

Attempts:

3 left

💡 Hint

Common Mistakes

Using localhost instead of the actual IP.

Using the wrong port number.

The replicaof command needs the master's IP and port. Here, 10.0.0.5 is the master IP and 6379 is the default Redis port.

5fill in blank

hard

Fill all three blanks to write a Redis replica configuration command with IP, port, and a comment.

Redis

# Set replica to master at [1]:[2]
replicaof [3] [2]

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

A192.168.10.20

B6379

D10.0.0.1

Attempts:

3 left

💡 Hint

Common Mistakes

Using different IPs in comment and command.

Mismatching port numbers.

The comment and command must match the master's IP and port. The IP 192.168.10.20 and port 6379 are used consistently.

Practice

1. What is the primary purpose of Redis replication?

easy

A. To compress data stored on disk

B. To delete old data from the database

C. To copy data from a master server to replicas automatically

D. To encrypt data during transmission

Solution

1. Step 1: Understand replication concept

   Replication means copying data from one server (master) to others (replicas) automatically.

2. Step 2: Identify the main goal

   This copying helps keep data safe and allows multiple servers to serve read requests.

3. Final Answer:

   To copy data from a master server to replicas automatically -> Option C

4. Quick Check:

   Replication = Data copying [OK]

Hint: Replication means copying data from master to replicas [OK]

Common Mistakes:

• Confusing replication with data deletion
• Thinking replication encrypts data
• Assuming replication compresses data

2. Which Redis command is used to configure a server as a replica of another?

easy

A. REPLICAOF <master_ip> <master_port>

B. CONNECT <master_ip> <master_port>

C. SYNC <master_ip> <master_port>

D. COPYFROM <master_ip> <master_port>

Solution

1. Step 1: Recall Redis replication commands

   Redis uses the command REPLICAOF (formerly SLAVEOF) to set a server as a replica.

2. Step 2: Check command correctness

   Only REPLICAOF accepts master IP and port to configure replication.

3. Final Answer:

   REPLICAOF <master_ip> <master_port> -> Option A

4. Quick Check:

   Replica config command = REPLICAOF [OK]

Hint: Use REPLICAOF to set replication target server [OK]

Common Mistakes:

• Using CONNECT which is not a Redis replication command
• Confusing SYNC with configuration command
• Inventing COPYFROM which does not exist

3. Given this Redis config snippet:

replicaof 192.168.1.10 6379
replica-read-only yes

What is the effect of replica-read-only yes?

medium

A. The replica rejects write commands and only allows reads

B. The replica can accept write commands from clients

C. The replica disables replication from the master

D. The replica automatically becomes a master

Solution

1. Step 1: Understand replica-read-only setting

   Setting replica-read-only to yes means the replica will not accept writes from clients.

2. Step 2: Identify behavior of replica

   The replica only allows read commands and rejects any write commands to keep data consistent with master.

3. Final Answer:

   The replica rejects write commands and only allows reads -> Option A

4. Quick Check:

   replica-read-only yes = read-only replica [OK]

Hint: replica-read-only yes means no writes allowed on replica [OK]

Common Mistakes:

• Thinking replica can write data with this setting
• Assuming replication stops with this option
• Believing replica becomes master automatically

4. You run replicaof 192.168.1.20 6379 on a Redis server but replication does not start. What is a likely cause?

medium

A. The command should be replicaof start instead

B. The master IP or port is incorrect or unreachable

C. The replica server has no data to replicate

D. Redis does not support replication

Solution

1. Step 1: Check network and master details

   If replication does not start, often the master IP or port is wrong or the replica cannot reach the master.

2. Step 2: Verify command correctness

   The command replicaof with IP and port is correct; no 'start' keyword is needed.

3. Final Answer:

   The master IP or port is incorrect or unreachable -> Option B

4. Quick Check:

   Replication fails if master unreachable [OK]

Hint: Check master IP and port if replication fails [OK]

Common Mistakes:

• Using wrong command syntax like replicaof start
• Assuming replication needs data on replica first
• Thinking Redis does not support replication

5. You want to set up a Redis replica that can serve read requests but also allow some writes during maintenance. Which configuration is best?

hard

A. Use replicaof <master_ip> <master_port> and set replica-read-only yes

B. Set the replica as master with no replication

C. Do not use replication; instead manually copy data

D. Use replicaof <master_ip> <master_port> and set replica-read-only no

Solution

1. Step 1: Understand replica-read-only option

   Setting replica-read-only to no allows writes on the replica, useful during maintenance.

2. Step 2: Combine with replication setup

   Using replicaof configures replication; setting replica-read-only no allows writes while still replicating.

3. Final Answer:

   Use replicaof <master_ip> <master_port> and set replica-read-only no -> Option D

4. Quick Check:

   replica-read-only no allows writes on replica [OK]

Hint: Set replica-read-only no to allow writes on replica [OK]

Common Mistakes:

• Assuming replica-read-only yes allows writes
• Thinking manual copy replaces replication
• Confusing replica with master roles