Node roles (master, data, ingest) in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of the cluster health API for a single master-eligible node?

Consider an Elasticsearch cluster with only one node configured as master-eligible but not data or ingest. What will the cluster.health API report for the number_of_data_nodes?

Elasticsearch

GET /_cluster/health

A {"number_of_data_nodes":0}

B {"number_of_data_nodes":1}

C {"number_of_data_nodes":-1}

D {"number_of_data_nodes":null}

💡 Hint

Master nodes do not hold data unless explicitly configured.

Master-eligible nodes manage cluster state but do not store data unless also configured as data nodes. Since this node is not a data node, number_of_data_nodes is 0.

❓ Predict Output

intermediate

What happens when an ingest node processes a document?

Given a node configured only as an ingest node, what is the expected behavior when a document is sent to it for indexing?

Elasticsearch

PUT /my-index/_doc/1
{
  "field": "value"
}

A The ingest node processes the document pipeline and forwards it to a data node for storage.

B The ingest node stores the document locally without forwarding.

C The ingest node rejects the document with an error.

D The ingest node converts the document to a master node for storage.

💡 Hint

Ingest nodes handle preprocessing but do not store data.

Ingest nodes apply pipelines to documents and then forward them to data nodes for storage. They do not store data themselves.

🧠 Conceptual

advanced

Which node role is responsible for cluster state management?

In Elasticsearch, which node role primarily manages the cluster state and coordinates cluster-wide actions?

A Data node

B Master-eligible node

C Ingest node

D Coordinating-only node

💡 Hint

Think about which node decides the cluster's overall health and configuration.

Master-eligible nodes manage the cluster state, elect the master, and coordinate cluster-wide operations.

❓ Predict Output

advanced

What error occurs if a data node is down during indexing?

Assume a cluster with one master-eligible node and one data node. If the data node is down and you try to index a document, what error will Elasticsearch return?

Elasticsearch

PUT /my-index/_doc/1
{
  "field": "value"
}

A {"error":{"type":"illegal_argument_exception","reason":"cannot index on master node"}}

B {"error":{"type":"index_not_found_exception","reason":"no such index"}}

C {"error":{"type":"unavailable_shards_exception","reason":"primary shard is not active"}}

D {"error":{"type":"cluster_block_exception","reason":"blocked by: [SERVICE_UNAVAILABLE/1/no master];"}}

💡 Hint

Think about shard availability on data nodes.

If the data node holding the primary shard is down, Elasticsearch cannot index the document and returns an unavailable_shards_exception.

🔧 Debug

expert

Why does this cluster fail to elect a master node?

Given a cluster with three nodes, all configured as node.data: true but node.master: false, why does the cluster fail to elect a master?

node1.yml:
node.master: false
node.data: true

node2.yml:
node.master: false
node.data: true

node3.yml:
node.master: false
node.data: true

A Data nodes cannot communicate with each other without a master node.

B The cluster name is missing, causing election failure.

C The cluster requires at least one ingest node to elect a master.

D No node is master-eligible, so no master election can occur.

💡 Hint

Master election requires at least one master-eligible node.

All nodes have node.master: false, so none can become master. Without a master-eligible node, the cluster cannot elect a master.