Adding and removing nodes in Redis - Step-by-Step Execution

Concept Flow - Adding and removing nodes

Start Cluster

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Add Node Command

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Cluster Updates Node List

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Node Joins Cluster

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Cluster Balances Slots

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Node Added Successfully

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Remove Node Command

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Cluster Removes Node

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Cluster Rebalances Slots

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Node Removed Successfully

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End

This flow shows how nodes are added or removed from a Redis cluster, updating the cluster state and slot distribution.

Execution Sample

Redis

redis-cli --cluster add-node 192.168.1.2:7003 192.168.1.1:7000
redis-cli --cluster del-node 192.168.1.1:7000 <node-id>

Commands to add a new node to the cluster and then remove a node by its ID.

Execution Table

Step	Command	Cluster State Change	Slots Rebalanced	Result
1	add-node 192.168.1.2:7003 192.168.1.1:7000	Node 7003 added to cluster node list	No slots yet	Node joins cluster
2	cluster update	Cluster updates slot allocation	Slots redistributed to include new node	Slots balanced
3	add-node complete	Cluster stable with new node	Slots balanced	Node added successfully
4	del-node <node-id>	Node removed from cluster node list	Slots from removed node reassigned	Node leaves cluster
5	cluster update	Cluster updates slot allocation	Slots redistributed among remaining nodes	Slots balanced
6	del-node complete	Cluster stable without removed node	Slots balanced	Node removed successfully
7	end	No further changes	No changes	Process complete

💡 Process ends after node is successfully added and then removed, cluster is stable.

Variable Tracker

Variable	Start	After Add 1	After Add 2	After Remove 1	After Remove 2	Final
Cluster Nodes	[7000,7001,7002]	[7000,7001,7002,7003]	[7000,7001,7002,7003]	[7000,7001,7002,7003]	[7000,7001,7002]	[7000,7001,7002]
Slot Allocation	Balanced among 3 nodes	Unbalanced (new node no slots)	Balanced among 4 nodes	Unbalanced (removed node slots unassigned)	Balanced among 3 nodes	Balanced among 3 nodes

Key Moments - 3 Insights

Why does the cluster need to rebalance slots after adding a node?

Because slots must be distributed evenly among all nodes to balance the data load, as shown in execution_table rows 2 and 3.

What happens to the slots of a node when it is removed?

The slots assigned to the removed node are reassigned to remaining nodes to keep the cluster balanced, as seen in execution_table rows 4 and 5.

Can a node join the cluster without slots assigned initially?

Yes, initially the new node has no slots until the cluster rebalances, as shown in execution_table row 1.

Visual Quiz - 3 Questions

Look at the execution_table, at which step are slots first redistributed to include the new node?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Check the 'Slots Rebalanced' column for when slots are redistributed.

According to variable_tracker, how many nodes are in the cluster after the node is removed?

A 2 nodes

B 4 nodes

C 3 nodes

D 1 node

💡 Hint

Look at 'Cluster Nodes' variable after 'After Remove 2' column.

If the cluster did not rebalance slots after removing a node, what would happen?

A Some slots would be unassigned

B New nodes would be added automatically

C Slots would remain balanced

D Cluster would shut down

💡 Hint

Refer to key_moments about slot reassignment after node removal.

Concept Snapshot

Redis Cluster node management:
- Add node with 'redis-cli --cluster add-node <new-node> <existing-node>'
- Remove node with 'redis-cli --cluster del-node <existing-node> <node-id>'
- Cluster updates node list and slot allocation after changes
- Slots must be balanced among nodes for data distribution
- Rebalancing happens automatically after add/remove

Full Transcript

This visual execution shows how Redis cluster nodes are added and removed. First, a new node is added using the add-node command, which updates the cluster's node list. Initially, the new node has no slots assigned. Then the cluster rebalances slots to distribute data evenly among all nodes. After the node is successfully added, a node can be removed using the del-node command by specifying its ID. The cluster removes the node from its list and reassigns the slots that belonged to the removed node to remaining nodes. This keeps the cluster balanced and stable. The variable tracker shows how the cluster nodes and slot allocation change step-by-step. Key moments clarify why rebalancing is necessary and what happens to slots during node removal. The quiz questions help reinforce understanding by referencing the execution steps and variable changes.