The cluster.initial_master_nodes setting is a crucial configuration parameter in Elasticsearch that specifies the initial set of master-eligible nodes for cluster bootstrap. It plays a vital role in the cluster formation process, especially when starting a new cluster for the first time.
- Default value: No default value; must be explicitly set for new clusters
- Possible values: A list of node names or IP addresses
- Recommendation: Set this value when bootstrapping a new cluster with multiple nodes
This setting is used to determine the initial set of master-eligible nodes that should join to form a new cluster. It helps prevent the "split-brain" problem by ensuring that only one cluster forms, even if multiple master-eligible nodes start independently.
Example and Effects
cluster.initial_master_nodes:
- node-1
- node-2
- node-3
In this example, we specify three nodes that are eligible to become the initial master. When starting a new cluster, you would set this on all master-eligible nodes.
You must set this when bootstrapping a new multi-node cluster to ensure proper cluster formation.
Proper configuration ensures that the cluster forms correctly and prevents split-brain scenarios during initial cluster startup.
Common Issues and Misuses
- Forgetting to remove the setting after the cluster is formed
- Incorrectly specifying node names or IP addresses
- Using this setting on an already formed cluster
Do's and Don'ts
Do's:
- Set this on all master-eligible nodes when bootstrapping a new cluster
- Use consistent values across all nodes
- Remove the setting after the cluster has formed successfully
Don'ts:
- Don't use this setting on an existing cluster
- Don't leave this setting in the configuration after initial cluster formation
- Don't use it for adding new nodes to an existing cluster
Frequently Asked Questions
Q: Do I need to set cluster.initial_master_nodes for a single-node cluster?
A: No, it's not necessary for single-node clusters. Elasticsearch can form a cluster automatically in this case.
Q: How many nodes should I list in cluster.initial_master_nodes?
A: It's recommended to list all master-eligible nodes in your initial cluster setup. For optimal fault tolerance, use an odd number of nodes, typically 3 or 5.
Q: Can I use IP addresses instead of node names in cluster.initial_master_nodes?
A: Yes, you can use either node names or IP addresses. However, using node names is generally preferred for clarity and flexibility.
Q: What happens if I don't set cluster.initial_master_nodes in a multi-node cluster?
A: Without this setting, master-eligible nodes may not be able to discover each other and form a cluster, leading to startup failures or multiple independent clusters.
Q: Should I keep cluster.initial_master_nodes in my configuration after the cluster is formed?
A: No, you should remove this setting after the cluster has successfully formed. It's only needed for the initial bootstrap process.
