Cross-cluster search in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Cross-cluster search in Elasticsearch?

Cross-cluster search allows you to search data across multiple Elasticsearch clusters as if they were one. It helps gather results from different places quickly.

intermediate

How do you configure a remote cluster for cross-cluster search?

You add the remote cluster's address to your local cluster settings using the cluster.remote.<name>.seeds setting. This tells your cluster where to find the remote one.

beginner

What is the role of the search request in cross-cluster search?

The search request can include remote cluster prefixes like cluster_name:index_name to specify which cluster and index to search in.

beginner

Can cross-cluster search be used to write data to remote clusters?

No, cross-cluster search is only for reading data across clusters. Writing data requires other methods like cross-cluster replication or direct indexing.

beginner

What are some benefits of using cross-cluster search?

It helps combine data from multiple clusters without moving data around. This improves search speed and keeps data organized in separate clusters.

What setting is used to add a remote cluster for cross-cluster search?

A index.remote.settings

B cluster.remote.<name>.seeds

C search.remote.cluster

D cluster.local.address

The cluster.remote.<name>.seeds setting specifies the addresses of remote clusters for cross-cluster search.

How do you specify a remote cluster index in a search query?

A Use <code>cluster_name:index_name</code> format

B Use <code>index_name@cluster_name</code> format

C Use <code>remote:index_name</code> format

D Use <code>index_name</code> only

You prefix the index with the remote cluster name like cluster_name:index_name to search that cluster.

Can cross-cluster search write data to remote clusters?

A Only if enabled in settings

B Yes, it can write and read data

C No, it only reads data

D Only for specific indices

Cross-cluster search is designed only for reading data across clusters, not writing.

What is a main advantage of cross-cluster search?

A Combining data from multiple clusters without moving it

B Faster data indexing

C Automatic data backup

D Improved data encryption

Cross-cluster search lets you search across clusters without copying data, saving time and storage.

Which Elasticsearch API is used to perform cross-cluster search?

A Index API

B Snapshot API

C Cluster API

D Search API

The Search API is used to query data across clusters in cross-cluster search.

Explain how to set up and use cross-cluster search in Elasticsearch.

Think about connecting clusters and how to ask for data from them.

Describe the benefits and limitations of cross-cluster search.

Consider what cross-cluster search can and cannot do.

Practice

1. What is the main purpose of cross-cluster search in Elasticsearch?

easy

A. To monitor cluster health status remotely

B. To backup data from one cluster to another

C. To merge two clusters into one

D. To search data across multiple Elasticsearch clusters using a single query

Solution

1. Step 1: Understand cross-cluster search concept

   Cross-cluster search allows querying data from multiple clusters in one search request.

2. Step 2: Differentiate from other cluster operations

   It does not merge clusters, backup data, or monitor health but focuses on searching data.

3. Final Answer:

   To search data across multiple Elasticsearch clusters using a single query -> Option D

4. Quick Check:

   Cross-cluster search = search across clusters [OK]

Hint: Cross-cluster search = one query, many clusters [OK]

Common Mistakes:

• Confusing search with backup or monitoring
• Thinking it merges clusters
• Assuming it manages cluster health

2. Which syntax correctly specifies a remote cluster alias in a cross-cluster search query?

easy

A. GET /remote_cluster:index/_search

B. GET /index@remote_cluster/_search

C. GET /index/remote_cluster/_search

D. GET /remote_cluster/_search/index

Solution

1. Step 1: Recall remote cluster alias syntax

   The correct syntax uses remote_cluster:index to specify the cluster alias and index.

2. Step 2: Check each option format

   Only GET /remote_cluster:index/_search matches the correct pattern: GET /remote_cluster:index/_search.

3. Final Answer:

   GET /remote_cluster:index/_search -> Option A

4. Quick Check:

   Alias:index/_search = correct syntax [OK]

Hint: Use alias:index/_search to target remote cluster data [OK]

Common Mistakes:

• Placing alias after index
• Using slashes instead of colon
• Misordering parts of the URL

3. Given this cross-cluster search query:

GET /clusterA:logs-2023/_search
{
  "query": { "match_all": {} }
}

What data will this query return?

medium

A. All documents from the local cluster's logs-2023 index

B. All documents from the logs-2023 index in clusterA

C. Documents matching "clusterA" in the logs-2023 index

D. An error because cluster alias is missing

Solution

1. Step 1: Identify cluster alias usage

   The query uses clusterA:logs-2023, meaning it targets the logs-2023 index on remote cluster named clusterA.

2. Step 2: Understand the query body

   The match_all query returns all documents from that index on clusterA.

3. Final Answer:

   All documents from the logs-2023 index in clusterA -> Option B

4. Quick Check:

   Alias:index with match_all = all remote docs [OK]

Hint: Alias:index means search that index on remote cluster [OK]

Common Mistakes:

• Assuming it searches local cluster
• Thinking it filters by cluster name in data
• Believing alias is optional

4. You run this cross-cluster search query:

GET /remoteCluster:products/_search
{
  "query": { "term": { "category": "electronics" } }
}

But get an error: no such remote cluster. What is the likely cause?

medium

A. The query syntax is invalid for cross-cluster search

B. The index 'products' does not exist on the remote cluster

C. The remote cluster alias 'remoteCluster' is not configured in the local cluster

D. The term query cannot be used in cross-cluster search

Solution

1. Step 1: Analyze the error message

   The error no such remote cluster means the alias 'remoteCluster' is unknown to the local cluster.

2. Step 2: Check configuration requirements

   Remote clusters must be configured before use; missing alias causes this error.

3. Final Answer:

   The remote cluster alias 'remoteCluster' is not configured in the local cluster -> Option C

4. Quick Check:

   Missing alias config = no such remote cluster error [OK]

Hint: Configure remote cluster alias before querying [OK]

Common Mistakes:

• Assuming index absence causes this error
• Blaming query syntax for alias errors
• Thinking term queries are unsupported

5. You want to search the sales-2023 index across two remote clusters named clusterX and clusterY. Which query correctly searches both clusters and returns combined results?

hard

A. GET /clusterX:sales-2023,clusterY:sales-2023/_search
{ "query": { "match_all": {} } }

B. GET /sales-2023/_search
{ "query": { "match_all": {} }, "clusters": ["clusterX", "clusterY"] }

C. GET /clusterX:clusterY:sales-2023/_search
{ "query": { "match_all": {} } }

D. GET /sales-2023/_search
{ "query": { "match_all": {} }, "remote_clusters": ["clusterX", "clusterY"] }

Solution

1. Step 1: Recall syntax for multiple remote clusters

   To search multiple clusters, use comma-separated list of <code>cluster_alias:index</code>, like <code>clusterX:sales-2023,clusterY:sales-2023</code>.

2. Step 2: Evaluate each option

   GET /clusterX:sales-2023,clusterY:sales-2023/_search { "query": { "match_all": {} } } uses <code>clusterX:sales-2023,clusterY:sales-2023</code> which is correct syntax for cross-cluster search across multiple clusters.

3. Final Answer:

   GET /clusterX:sales-2023,clusterY:sales-2023/_search { "query": { "match_all": {} } } -> Option A

4. Quick Check:

   clusterX:sales-2023,clusterY:sales-2023/_search = multi-cluster search [OK]

Hint: comma-separate alias:index for multi-cluster search [OK]

Common Mistakes:

• Using multiple colons instead of commas
• Adding cluster names inside query body
• Assuming local index searches multiple clusters