Cluster health API in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Cluster Health API in Elasticsearch?

The Cluster Health API provides information about the health status of an Elasticsearch cluster, including the status of nodes, shards, and indices to help monitor cluster stability and performance.

beginner

What are the possible health status values returned by the Cluster Health API?

The health status can be green (all primary and replica shards are active), yellow (all primary shards are active but some replicas are not), or red (some primary shards are not active).

beginner

How do you request the cluster health status using the Elasticsearch REST API?

You send a GET request to /_cluster/health. For example: GET /_cluster/health returns the overall cluster health.

intermediate

What does the wait_for_status parameter do in the Cluster Health API?

It makes the API call wait until the cluster reaches the specified health status (green, yellow, or red) or until a timeout occurs, useful for monitoring or automation.

intermediate

What key information does the Cluster Health API response include?

The response includes cluster name, status, number of nodes, number of data nodes, active primary shards, active shards, relocating shards, initializing shards, unassigned shards, and timed_out flag.

Which HTTP method is used to check cluster health in Elasticsearch?

A DELETE

B GET

C PUT

D POST

The Cluster Health API uses the GET method to retrieve health information.

What does a 'yellow' status mean in cluster health?

A All primary shards are active but some replicas are not

B Some primary shards are not active

C All primary and replica shards are active

D Cluster is offline

Yellow means all primary shards are active but some replica shards are not.

Which parameter makes the Cluster Health API wait for a specific status?

A wait_for_nodes

B level

C timeout

D wait_for_status

The 'wait_for_status' parameter waits until the cluster reaches the specified health status.

What does the 'timed_out' field in the response indicate?

A The API call timed out before reaching the desired status

B The cluster is down

C The cluster is healthy

D The API call was successful

The 'timed_out' field shows if the API call timed out waiting for the cluster to reach the requested status.

Which endpoint is used to get health information for a specific index?

A /_cluster/health

B /index_name/_health

C /_cluster/health/index_name

D /_health/index_name

You append the index name to the cluster health endpoint to get health info for that index.

Explain how the Cluster Health API helps monitor an Elasticsearch cluster.

Think about what information you get and how it shows cluster stability.

Describe the meaning of green, yellow, and red statuses in the Cluster Health API.

Relate the colors to shard availability.

Practice

1. What does the Elasticsearch Cluster Health API primarily provide?

easy

A. The current health status of the Elasticsearch cluster

B. The list of all documents in the cluster

C. The configuration settings of the cluster nodes

D. The query performance statistics

Solution

1. Step 1: Understand the purpose of Cluster Health API

   The Cluster Health API is designed to report the health status of the Elasticsearch cluster, such as green, yellow, or red status.

2. Step 2: Compare with other options

   Options B, C, and D relate to documents, configuration, and performance, which are not the main focus of the Cluster Health API.

3. Final Answer:

   The current health status of the Elasticsearch cluster -> Option A

4. Quick Check:

   Cluster Health API = Cluster health status [OK]

Hint: Cluster Health API shows cluster status, not data or config [OK]

Common Mistakes:

• Confusing cluster health with document data
• Thinking it shows node configuration
• Assuming it reports query stats

2. Which of the following is the correct syntax to get the cluster health using Elasticsearch REST API?

easy

A. GET /_cluster/health

B. POST /_cluster/health

C. GET /_cluster/status

D. POST /_health/cluster

Solution

1. Step 1: Recall the correct HTTP method and endpoint

   The Cluster Health API uses the GET method with the endpoint /_cluster/health.

2. Step 2: Eliminate incorrect options

   POST is not used for this API, and the endpoint must be exactly /_cluster/health. Options C and D have wrong endpoints.

3. Final Answer:

   GET /_cluster/health -> Option A

4. Quick Check:

   GET + /_cluster/health = Correct syntax [OK]

Hint: Use GET method with /_cluster/health endpoint [OK]

Common Mistakes:

• Using POST instead of GET
• Wrong endpoint like /_cluster/status
• Mixing endpoint parts

3. What will be the output status if the cluster has all primary and replica shards allocated properly?

medium

A. "status": "red"

B. "status": "yellow"

C. "status": "blue"

D. "status": "green"

Solution

1. Step 1: Understand cluster health statuses

   Green means all primary and replica shards are allocated properly, yellow means replicas missing but primaries allocated, red means some primaries missing.

2. Step 2: Match the condition to status

   Since all primary and replica shards are allocated, the status is green.

3. Final Answer:

   "status": "green" -> Option D

4. Quick Check:

   All shards allocated = green status [OK]

Hint: Green means all shards allocated, yellow means some replicas missing [OK]

Common Mistakes:

• Confusing yellow with green
• Thinking red means healthy
• Assuming blue is a valid status

4. You run GET /_cluster/health?level=shards but get an error. What is the likely cause?

medium

A. The query parameter should be detail=shards instead

B. The HTTP method should be POST, not GET

C. The level parameter does not accept 'shards' as a value

D. The endpoint should be /_cluster/status

Solution

1. Step 1: Check valid values for level parameter

   The Cluster Health API accepts level values like 'cluster', 'indices', and 'shards'. However, 'shards' is only supported in newer versions and may cause errors if unsupported.

2. Step 2: Analyze other options

   GET is correct method, endpoint is correct, and detail is not a valid parameter for this API.

3. Final Answer:

   The level parameter does not accept 'shards' as a value -> Option C

4. Quick Check:

   Invalid level value causes error [OK]

Hint: Check if 'level=shards' is supported in your Elasticsearch version [OK]

Common Mistakes:

• Using POST instead of GET
• Wrong endpoint /_cluster/status
• Using invalid query parameters

5. You want to monitor your cluster health and get detailed info about each index's health. Which API call should you use?

hard

A. GET /_cluster/health?level=cluster

B. GET /_cluster/health?level=indices

C. GET /_cluster/state?filter_path=metadata.indices

D. GET /_nodes/stats

Solution

1. Step 1: Identify the parameter for detailed index health

   The level=indices parameter in the Cluster Health API returns health info for each index.

2. Step 2: Compare with other options

   level=cluster gives overall cluster health only; /_cluster/state and /_nodes/stats provide different info unrelated to health per index.

3. Final Answer:

   GET /_cluster/health?level=indices -> Option B

4. Quick Check:

   Use level=indices for per-index health details [OK]

Hint: Use level=indices to get health info per index [OK]

Common Mistakes:

• Using level=cluster for detailed index info
• Confusing cluster state with health API
• Requesting node stats instead of health