Scaling and Shrinking a ClickHouse Cluster (Best Practices for Dynamically Adding Nodes)

What is Cluster Scaling and Shrinking?

In ClickHouse, cluster scaling and shrinking refer to the process of dynamically adding or removing nodes, which helps meet changing business requirements.

Why Do We Need to Scale and Shrink a Cluster?

When business demands suddenly increase, it's necessary to quickly scale up the cluster to handle increased load. In ClickHouse, this can be achieved by dynamically adding new nodes. Similarly, when business demands decrease, resources can be saved by removing nodes.

How to Scale Up a Cluster

1. Obtain information about the new node: First, you need to get details such as the IP address, port number, and memory of this new node.

2. Add the new node to the cluster: Use ClickHouse's API or CLI commands to add the new node to the cluster. There are several specific commands available:

    clickhouse-client --host  --port  --username  --password 

    const cluster = await Cluster.connect({
      host: '',
      port: ,
      user: '',
      password: ''
    });
    await cluster.addNode();

3. Restart all nodes: To ensure the successful addition of the new node, you need to restart all nodes in the cluster.

How to Shrink a Cluster

1. Check the total number of current nodes in the cluster: First, it is necessary to understand how many nodes are currently in the cluster.

2. Remove a node from the cluster: Use ClickHouse's API or CLI commands to remove one node, thereby reducing the size of the cluster.

    clickhouse-client --host  --port  --username  --password 

    const cluster = await Cluster.connect({
      host: '',
      port: ,
      user: '',
      password: ''
    });
    await cluster.removeNode();

3. Restart all nodes: To ensure the removal was successful, you need to restart all nodes in the cluster.

Best Practices

1. Check before scaling up or down a cluster: Ensure that the node(s) required for expansion or shrinking are ready and have no running tasks.

2. Perform operations using CLI commands: CLI commands are more convenient for dynamically adding and removing nodes. API commands can be used to implement some more complex operations, but they may be better suited for large distributed systems.

3. Monitor cluster status: Ensure all nodes are in a normal state; this guarantees the safety and reliability of data.

Conclusion

Scaling up or down ClickHouse clusters is a dynamic operation performed to meet changing business requirements. By effectively adding new nodes when necessary and removing unused ones, you can significantly improve the scalability and reliability of your cluster.