Replica management in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Elasticsearch replica setting query?

Given the following request to update the number of replicas for an index, what will be the number of replicas after the update?

Elasticsearch

PUT /my-index/_settings
{
  "index" : {
    "number_of_replicas" : 2
  }
}

A The request will fail with a syntax error.

B The index will have 0 replicas per shard.

C The index will have 1 replica per shard.

D The index will have 2 replicas per shard.

💡 Hint

The number_of_replicas setting controls how many copies of each shard exist besides the primary.

The PUT request sets the number_of_replicas to 2, so each primary shard will have 2 replica shards.

❓ Predict Output

intermediate

What happens if you set number_of_replicas to 0?

Consider this request to update an index's replica count: PUT /logs/_settings { "index": { "number_of_replicas": 0 } } What is the effect on the index?

Elasticsearch

PUT /logs/_settings
{
  "index": {
    "number_of_replicas": 0
  }
}

A The request will cause an error because replicas cannot be zero.

B The index will have one replica shard per primary shard.

C The index will have no replica shards, only primary shards.

D The index will have two replica shards per primary shard.

💡 Hint

Replicas provide copies of data for fault tolerance. Zero means no copies.

Setting number_of_replicas to 0 means the index will have only primary shards and no replicas.

❓ Predict Output

advanced

What error does this replica setting update cause?

What error will this request produce? PUT /data/_settings { "index": { "number_of_replicas": -1 } }

Elasticsearch

PUT /data/_settings
{
  "index": {
    "number_of_replicas": -1
  }
}

A 400 Bad Request: number_of_replicas must be >= 0

B 200 OK: number_of_replicas set to -1

C 500 Internal Server Error

D 404 Not Found: index does not exist

💡 Hint

Replica count cannot be negative.

Elasticsearch validates that number_of_replicas is zero or positive. Negative values cause a 400 error.

🧠 Conceptual

advanced

How does replica count affect search availability during node failure?

If an Elasticsearch cluster has 1 replica per shard and one data node fails, what happens to search availability for the shards on that node?

A Search fails because primary shards are lost and replicas are not used.

B Search continues without interruption because replicas serve the requests.

C Search is slower but still works because replicas are rebuilt from scratch.

D Search stops until the failed node is back online.

💡 Hint

Replicas provide copies that can serve search requests if primaries fail.

With replicas, if a node holding primary shards fails, the replicas on other nodes serve search requests, keeping availability.

❓ Predict Output

expert

What is the number of shards and replicas after this index creation?

Given this index creation request, how many total shards (primary + replicas) will the index have? PUT /analytics { "settings": { "number_of_shards": 3, "number_of_replicas": 2 } }

Elasticsearch

PUT /analytics
{
  "settings": {
    "number_of_shards": 3,
    "number_of_replicas": 2
  }
}

A 9 total shards: 3 primary + 6 replicas

B 6 total shards: 3 primary + 3 replicas

C 3 total shards: 3 primary only

D 5 total shards: 3 primary + 2 replicas

💡 Hint

Total shards = primary shards + (primary shards × number_of_replicas).

With 3 primary shards and 2 replicas each, total shards = 3 + (3×2) = 9.