Adding and removing nodes in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does adding a node mean in a Redis cluster?

Adding a node means introducing a new Redis server to the cluster to share the data and workload, improving capacity and availability.

intermediate

How do you safely remove a node from a Redis cluster?

You first migrate the data from the node to be removed to other nodes, then use the cluster command to forget the node, ensuring no data loss.

beginner

What is the purpose of the 'CLUSTER MEET' command in Redis?

The 'CLUSTER MEET' command is used to add a new node to an existing Redis cluster by making nodes aware of each other.

intermediate

Why must slots be migrated when removing a node from a Redis cluster?

Slots hold the data keys. Migrating slots ensures data is moved safely to other nodes before removing the node, preventing data loss.

intermediate

What command helps to forget a node in a Redis cluster after removal?

The 'CLUSTER FORGET ' command removes the node from the cluster's configuration after its data has been migrated.

Which command is used to introduce a new node to a Redis cluster?

A CLUSTER MIGRATE

B CLUSTER FORGET

C CLUSTER MEET

D CLUSTER ADDNODE

CLUSTER MEET is the command that makes nodes aware of each other to form or expand a cluster.

Before removing a node, what must be done with its slots?

A Migrate them to other nodes

B Backup them locally

C Delete them immediately

D Ignore them

Slots must be migrated to other nodes to preserve data before removing a node.

What does the 'CLUSTER FORGET' command do?

A Removes a node from the cluster configuration

B Adds a node to the cluster

C Migrates slots between nodes

D Lists all nodes in the cluster

CLUSTER FORGET removes a node from the cluster's configuration after it is removed.

Why add nodes to a Redis cluster?

A To reduce data storage

B To increase capacity and availability

C To slow down queries

D To delete data

Adding nodes helps the cluster handle more data and stay available if some nodes fail.

What happens if you remove a node without migrating its slots?

A Nothing happens

B Cluster automatically backs up data

C Other nodes take over slots automatically

D Data on that node is lost

Removing a node without migrating slots causes data loss for keys in those slots.

Explain the steps to add a new node to a Redis cluster.

Think about how nodes become aware of each other and share data.

Describe how to safely remove a node from a Redis cluster without losing data.

Focus on data migration and cluster configuration update.

Practice

1. What is the primary purpose of adding nodes to a Redis cluster?

easy

A. To increase the cluster's capacity and distribute data

B. To delete all data from the cluster

C. To backup the cluster data

D. To change the Redis version on all nodes

Solution

1. Step 1: Understand what adding nodes means

   Adding nodes means increasing the number of servers in the cluster to share the data load.

2. Step 2: Identify the effect of adding nodes

   More nodes mean more capacity and better data distribution across the cluster.

3. Final Answer:

   To increase the cluster's capacity and distribute data -> Option A

4. Quick Check:

   Adding nodes = More capacity and distribution [OK]

Hint: Adding nodes grows cluster capacity and data spread [OK]

Common Mistakes:

• Thinking adding nodes deletes data
• Confusing adding nodes with backup
• Assuming adding nodes upgrades Redis version

2. Which of the following is the correct syntax to add a node to a Redis cluster using redis-cli?

easy

A. redis-cli --cluster add-node :<port> :<port>

B. redis-cli --cluster remove-node :<port>

C. redis-cli --cluster create-node :<port>

D. redis-cli --cluster add :<port>

Solution

1. Step 1: Recall the command to add a node

   The correct command uses --cluster add-node followed by the new node and an existing node in the cluster.

2. Step 2: Match the syntax

   redis-cli --cluster add-node :<port> :<port> matches the correct syntax: redis-cli --cluster add-node new-node existing-node.

3. Final Answer:

   redis-cli --cluster add-node <new-node-ip>:<port> <existing-node-ip>:<port> -> Option A

4. Quick Check:

   Correct add-node syntax = redis-cli --cluster add-node :<port> :<port> [OK]

Hint: Add node command uses --cluster add-node with new and existing nodes [OK]

Common Mistakes:

• Using remove-node instead of add-node
• Using create-node which does not exist
• Omitting existing node IP in command

3. Given the command redis-cli --cluster del-node 192.168.1.5:7000 07c37dfeb2352e03a5a1e1f3a2f8b9a1f2e3d4c5, what will happen?

medium

A. A new node will be added at 192.168.1.5:7000

B. The node at 192.168.1.5:7000 will be removed from the cluster

C. The cluster will be created with the given node ID

D. The command will fail due to wrong syntax

Solution

1. Step 1: Understand the del-node command

   The command redis-cli --cluster del-node removes a node from the cluster using its IP and node ID.

2. Step 2: Analyze the given command

   The command specifies the node IP and the node ID, so it will remove that node from the cluster.

3. Final Answer:

   The node at 192.168.1.5:7000 will be removed from the cluster -> Option B

4. Quick Check:

   del-node removes specified node [OK]

Hint: del-node removes node by IP and node ID [OK]

Common Mistakes:

• Confusing del-node with add-node
• Thinking it adds a node
• Assuming command syntax is incorrect

4. You run redis-cli --cluster add-node 192.168.1.10:7003 192.168.1.11:7000 but get an error. What is the most likely cause?

medium

A. The new node is already part of the cluster

B. The existing node IP is incorrect

C. The command should be --cluster del-node instead

D. Redis server is not running on the new node

Solution

1. Step 1: Check prerequisites for adding a node

   The new node must be running Redis and reachable for the add-node command to succeed.

2. Step 2: Identify common causes of add-node failure

   If Redis is not running on the new node, the command will fail because it cannot connect.

3. Final Answer:

   Redis server is not running on the new node -> Option D

4. Quick Check:

   New node must run Redis to add [OK]

Hint: New node must be running Redis before adding [OK]

Common Mistakes:

• Assuming IP typo without checking server status
• Confusing add-node with del-node command
• Ignoring that Redis must run on new node

5. You want to remove a node from a Redis cluster but keep its data safe. Which sequence of commands should you use?

hard

A. Use redis-cli --cluster del-node then backup data manually

B. Directly stop the Redis server on the node and remove it

C. Use redis-cli --cluster reshard to move slots, then redis-cli --cluster del-node

D. Use redis-cli --cluster add-node to replace the node

Solution

1. Step 1: Understand data safety when removing nodes

   Removing a node without moving its data causes data loss.

2. Step 2: Use reshard to move data slots

   Resharding moves the data slots from the node to be removed to other nodes safely.

3. Step 3: Remove the node after resharding

   After data is moved, del-node safely removes the node without data loss.

4. Final Answer:

   Use redis-cli --cluster reshard to move slots, then redis-cli --cluster del-node -> Option C

5. Quick Check:

   Reshard then del-node = safe removal [OK]

Hint: Reshard slots before removing node to keep data safe [OK]

Common Mistakes:

• Removing node without moving data first
• Stopping server directly causing data loss
• Confusing add-node with removal process