Replica management in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a replica in Elasticsearch?

A replica is a copy of a primary shard in Elasticsearch. It provides fault tolerance and improves search performance by distributing the load.

beginner

How do replicas improve Elasticsearch availability?

Replicas allow Elasticsearch to continue serving data even if a primary shard fails, because the replica shard can take over without data loss.

intermediate

How can you change the number of replicas for an existing Elasticsearch index?

You can update the number of replicas using the Update Index Settings API with a command like: <br>PUT /my_index/_settings { "index": { "number_of_replicas": 2 } }

intermediate

What happens if you set the number of replicas to 0 in Elasticsearch?

Setting replicas to 0 means there are no copies of primary shards. This reduces fault tolerance and search performance but saves disk space.

intermediate

Can replicas be allocated on the same node as their primary shards?

No. Elasticsearch ensures replicas are allocated on different nodes than their primary shards to avoid data loss if a node fails.

What is the main purpose of replicas in Elasticsearch?

A To provide fault tolerance and improve search speed

B To store backup data on the same node

C To reduce the number of shards

D To increase indexing speed only

Replicas provide copies of primary shards on different nodes to protect against failure and improve search performance.

How do you change the number of replicas for an index?

A Using the Update Index Settings API

B By deleting and recreating the index

C By changing the cluster settings only

D By restarting Elasticsearch

You update the number of replicas with the Update Index Settings API without needing to recreate the index.

If a primary shard fails, what happens to its replica shard?

A It is deleted automatically

B It remains inactive

C It becomes the new primary shard

D It merges with other shards

The replica shard is promoted to primary to keep the data available.

Can replicas be stored on the same node as their primary shards?

A Yes, always on the same node

B No, replicas are stored on different nodes

C Only if manually configured

D Only for small clusters

Elasticsearch automatically places replicas on different nodes to avoid data loss.

What is a consequence of setting number_of_replicas to 0?

A Indexing speed decreases

B More disk space is used

C Search performance improves

D No replicas exist, reducing fault tolerance

With zero replicas, there are no copies of data, so if a primary shard fails, data is unavailable.

Explain what replicas are in Elasticsearch and why they are important.

Think about how Elasticsearch keeps data safe and fast to search.

Describe how to change the number of replicas for an existing index and what effect it has.

Consider the command to update settings and what happens after.