Cluster architecture in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of the command CLUSTER INFO in Redis Cluster?

You run the Redis command CLUSTER INFO on a node in a Redis Cluster. What kind of information does this command return?

A It returns the cluster state, number of slots assigned, number of known nodes, and cluster size.

B It returns the list of all keys stored in the cluster.

C It returns the memory usage of the Redis server.

D It returns the current connected clients and their IP addresses.

💡 Hint

Think about what general cluster status information you might want to check.

The CLUSTER INFO command provides high-level information about the cluster's state, including how many slots are assigned and the cluster size.

🧠 Conceptual

intermediate

How does Redis Cluster handle key distribution?

In Redis Cluster, how are keys distributed across different nodes?

A Keys are stored on all nodes simultaneously for redundancy.

B Keys are assigned randomly to any node without hashing.

C Keys are assigned to nodes based on hashing the key into one of 16384 slots, which are distributed among nodes.

D Keys are stored only on the master node and replicas do not hold keys.

💡 Hint

Think about how consistent hashing or slot assignment works in distributed systems.

Redis Cluster uses a fixed number of hash slots (16384). Each key is hashed to one slot, and slots are assigned to nodes, distributing keys evenly.

📝 Syntax

advanced

Which command correctly adds a new node to an existing Redis Cluster?

You want to add a new node to your Redis Cluster. Which command syntax is correct for this operation?

A redis-cli --cluster create <new_node_ip>:<port>

B redis-cli --cluster add-node <new_node_ip>:<port> <existing_node_ip>:<port>

C redis-cli --cluster join <new_node_ip>:<port> <existing_node_ip>:<port>

D redis-cli --cluster insert <new_node_ip>:<port> <existing_node_ip>:<port>

💡 Hint

Look for the official command to add a node to a cluster.

The correct command to add a node to an existing Redis Cluster is redis-cli --cluster add-node followed by the new node and an existing node.

❓ optimization

advanced

How can you optimize Redis Cluster to handle failover smoothly?

Which configuration or setup helps Redis Cluster handle failover smoothly without data loss?

A Manually restart nodes when a failure occurs.

B Disable replicas to reduce network traffic.

C Use a single master node with no replicas for simplicity.

D Assign replicas to each master node so replicas can take over if a master fails.

💡 Hint

Think about how redundancy helps in failover scenarios.

Having replicas assigned to each master allows automatic failover if a master node fails, improving cluster availability.

🔧 Debug

expert

What error occurs if you try to run a multi-key command on keys located in different Redis Cluster slots?

You run the command MGET key1 key2 where key1 and key2 hash to different slots in a Redis Cluster. What error will Redis return?

A CROSSSLOT Keys in request don't hash to the same slot

B WRONGTYPE Operation against a key holding the wrong kind of value

C OOM command not allowed when used memory > 'maxmemory'.

D NOSCRIPT No matching script. Please use EVAL.

💡 Hint

Think about Redis Cluster's slot-based key distribution and multi-key command restrictions.

Redis Cluster requires all keys in a multi-key command to be in the same hash slot. Otherwise, it returns a CROSSSLOT error.