Shard allocation awareness in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is shard allocation awareness in Elasticsearch?

Shard allocation awareness is a feature that helps Elasticsearch place shards on different nodes based on specific attributes, like rack or zone, to improve fault tolerance and availability.

beginner

Why is shard allocation awareness important?

It ensures that copies of data (shards) are spread across different physical locations or failure domains, so if one location fails, data remains available from another.

intermediate

How do you configure shard allocation awareness in Elasticsearch?

You set node attributes (like zone or rack) and then configure cluster.routing.allocation.awareness.attributes with those attribute names to tell Elasticsearch to spread shards accordingly.

intermediate

What happens if Elasticsearch cannot satisfy shard allocation awareness rules?

Elasticsearch may delay shard allocation or allocate shards on the same attribute value, risking reduced fault tolerance until the cluster state changes.

beginner

Example: If nodes have attribute zone with values zone1 and zone2, how does shard allocation awareness use this?

Elasticsearch tries to place primary and replica shards on nodes in different zones, so if zone1 fails, data is still available in zone2.

What does shard allocation awareness help prevent?

A More shards per node

B All shard copies being on the same failure domain

C Faster indexing speed

D Automatic data backup to cloud

Shard allocation awareness prevents all copies of a shard from being placed on the same failure domain, like the same rack or zone.

Which Elasticsearch setting controls shard allocation awareness?

A cluster.shard.allocation.awareness

B node.attr.shard.awareness

C index.shard.awareness.enabled

D cluster.routing.allocation.awareness.attributes

The correct setting is cluster.routing.allocation.awareness.attributes, which lists node attributes to consider for shard placement.

If you want to spread shards across data centers, what should you do?

A Increase number of shards

B Disable shard allocation awareness

C Set node attributes for data center and use shard allocation awareness

D Use only one node

You assign node attributes representing data centers and configure shard allocation awareness to spread shards accordingly.

What is a node attribute in Elasticsearch shard allocation awareness?

A A label assigned to a node to group it by physical or logical location

B The number of shards on a node

C The IP address of the node

D The node's CPU speed

Node attributes are labels like 'zone' or 'rack' used to group nodes for shard placement decisions.

What happens if all nodes share the same attribute value in shard allocation awareness?

A Elasticsearch may place all shards on the same attribute value, reducing fault tolerance

B Elasticsearch refuses to allocate shards

C Shards are automatically deleted

D Shard allocation awareness is ignored

If all nodes have the same attribute value, Elasticsearch cannot spread shards across different values, so fault tolerance is reduced.

Explain shard allocation awareness and why it matters in Elasticsearch.

Think about how Elasticsearch keeps data safe across different physical locations.

Describe how to configure shard allocation awareness in an Elasticsearch cluster.

Consider what labels you give nodes and how Elasticsearch uses them.