Adding and removing nodes in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of adding a new node to a Redis cluster?

You have a Redis cluster with 3 nodes. You run the command to add a new node to the cluster. What will the cluster nodes list show after adding the new node but before resharding?

Redis

redis-cli --cluster add-node 192.168.1.4:7004 192.168.1.1:7000
redis-cli --cluster nodes 192.168.1.1:7000

A The new node appears in the cluster nodes list with no slots assigned.

B The new node appears with all slots assigned to it.

C The new node does not appear until resharding is done.

D The cluster nodes list shows an error because slots are not balanced.

💡 Hint

Think about what happens immediately after adding a node before moving slots.

When you add a new node to a Redis cluster, it joins the cluster but initially has no hash slots assigned. Slots must be manually resharded to the new node.

❓ query_result

intermediate

What happens when you remove a node that holds slots without resharding?

In a Redis cluster, you remove a node that currently holds hash slots without migrating its slots first. What will be the state of the cluster?

Redis

redis-cli --cluster del-node 192.168.1.2:7002 <node-id>

A The node is removed and slots are lost but cluster continues normally.

B The cluster automatically migrates slots to other nodes.

C The cluster enters an error state and refuses writes to affected slots.

D The command fails because slots must be migrated before removal.

💡 Hint

Consider what happens to data when slots are suddenly missing.

Removing a node that holds slots without migrating them causes the cluster to lose those slots, leading to an error state and inability to serve keys in those slots.

📝 Syntax

advanced

Which command correctly adds a node to a Redis cluster?

You want to add a new node at IP 10.0.0.5 port 7005 to an existing cluster with a node at 10.0.0.1 port 7000. Which command is syntactically correct?

A redis-cli --cluster add-node 10.0.0.5:7005 10.0.0.1:7000

B redis-cli --cluster add-node 10.0.0.1:7000 10.0.0.5:7005

C redis-cli --cluster add-node --node 10.0.0.5:7005 --cluster 10.0.0.1:7000

D redis-cli --add-node 10.0.0.5:7005 10.0.0.1:7000

💡 Hint

The syntax is: redis-cli --cluster add-node

The correct syntax for adding a node is to specify the new node address first, then an existing cluster node address.

❓ optimization

advanced

Best practice to minimize downtime when removing a Redis cluster node

You want to remove a node from a Redis cluster with minimal downtime. Which approach is best?

A Remove the node and rely on cluster auto-recovery to fix slots.

B Migrate slots from the node to be removed to other nodes, then remove the node.

C Remove the node immediately and then reshard slots manually.

D Stop the entire cluster, remove the node, then restart the cluster.

💡 Hint

Think about how to keep data available during node removal.

Migrating slots before removal ensures data is available on other nodes, preventing downtime.

🧠 Conceptual

expert

Why is it important to reshard slots after adding a new node to a Redis cluster?

After adding a new node to a Redis cluster, why must you reshard slots to the new node?

A To update the cluster configuration file automatically.

B Because Redis requires manual slot assignment for security reasons.

C Because the new node cannot join the cluster without slots.

D To balance the data load and improve cluster performance.

💡 Hint

Think about what happens if slots are unevenly distributed.

Resharding distributes hash slots to the new node, balancing data and load across the cluster.