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.

Practice

1.

What is the primary role of a master node in Elasticsearch?

easy

A. Manage cluster-wide settings and coordinate nodes

B. Store and manage the actual data

C. Process incoming documents before indexing

D. Serve as a backup node for data recovery

Solution

1. Step 1: Understand node roles in Elasticsearch

   The master node is responsible for managing the cluster state and coordinating nodes.

2. Step 2: Differentiate master from other roles

   Data nodes store data, and ingest nodes process documents. Master nodes handle cluster-wide tasks.

3. Final Answer:

   Manage cluster-wide settings and coordinate nodes -> Option A

4. Quick Check:

   Master node = cluster coordination [OK]

Hint: Master node controls cluster settings and coordination [OK]

Common Mistakes:

• Confusing master node with data node
• Thinking ingest node manages cluster
• Assuming master stores data

2.

Which of the following is the correct way to assign a node as a data node in the elasticsearch.yml configuration file?

node.roles: [ ? ]

easy

A. ["master"]

B. ["data"]

C. ["ingest"]

D. ["coordinating"]

Solution

1. Step 1: Identify the role name for data nodes

   Data nodes are assigned the role "data" in the node.roles setting.

2. Step 2: Match the correct syntax

   The correct syntax uses a list with the string "data" inside square brackets and quotes.

3. Final Answer:

   ["data"] -> Option B

4. Quick Check:

   node.roles: ["data"] assigns data node role [OK]

Hint: Use node.roles: ["data"] to assign data node role [OK]

Common Mistakes:

• Using incorrect role names like "coordinating"
• Omitting quotes around role names
• Assigning master role instead of data

3.

Given this node configuration snippet in elasticsearch.yml:

node.roles: ["master", "ingest"]

Which tasks will this node perform?

medium

A. Only manage cluster state

B. Only process incoming documents

C. Manage cluster state and process incoming documents

D. Store data and manage cluster state

Solution

1. Step 1: Analyze the assigned roles

   The node has roles "master" and "ingest", so it can do both tasks.

2. Step 2: Understand what each role does

   Master manages cluster state; ingest processes incoming documents before indexing.

3. Final Answer:

   Manage cluster state and process incoming documents -> Option C

4. Quick Check:

   Roles master + ingest = cluster + document processing [OK]

Hint: Multiple roles mean combined tasks of those roles [OK]

Common Mistakes:

• Assuming node can only have one role
• Confusing ingest with data node role
• Ignoring master role effects

4.

Look at this elasticsearch.yml snippet:

node.roles: master, data

What is the problem with this configuration?

medium

A. Roles must be listed as a YAML list with brackets and quotes

B. The roles "master" and "data" cannot be assigned together

C. The roles should be uppercase

D. The node.roles setting is deprecated

Solution

1. Step 1: Check YAML syntax for node.roles

   Roles must be defined as a list, e.g., ["master", "data"], not as a comma-separated string.

2. Step 2: Validate role assignment rules

   Assigning master and data roles together is allowed; roles are lowercase; node.roles is valid.

3. Final Answer:

   Roles must be listed as a YAML list with brackets and quotes -> Option A

4. Quick Check:

   YAML list syntax required for node.roles [OK]

Hint: Use YAML list syntax: node.roles: ["master", "data"] [OK]

Common Mistakes:

• Writing roles as comma-separated string without brackets
• Using uppercase role names
• Thinking roles cannot combine

5.

You want to create a node that only processes incoming documents but does not store data or manage cluster state. Which node.roles setting should you use?

hard

A. ["master", "data"]

B. ["data"]

C. ["master"]

D. ["ingest"]

Solution

1. Step 1: Identify the role for processing incoming documents

   The ingest role processes incoming documents before indexing.

2. Step 2: Exclude roles that store data or manage cluster

   Data role stores data; master manages cluster state. We want neither.

3. Final Answer:

   ["ingest"] -> Option D

4. Quick Check:

   Only ingest role processes documents without storing or managing [OK]

Hint: Use node.roles: ["ingest"] for document processing only [OK]

Common Mistakes:

• Choosing data role which stores data
• Choosing master role which manages cluster
• Combining roles unnecessarily