Cluster, node, and shard architecture in Elasticsearch - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a cluster name in Elasticsearch configuration.

Elasticsearch

cluster.name: [1]

Drag options to blanks, or click blank then click option'

Anode-1

B"my-cluster"

Cshard-0

Dindex-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a node name instead of a cluster name

Omitting quotes around the cluster name

The cluster.name setting defines the name of the Elasticsearch cluster.

2fill in blank

medium

Complete the code to set the node name in Elasticsearch configuration.

Elasticsearch

node.name: [1]

Drag options to blanks, or click blank then click option'

A"index-1"

B"cluster-1"

C"node-1"

D"shard-1"

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing node name with cluster name

Using shard or index names as node names

The node.name setting specifies the name of the node within the cluster.

3fill in blank

hard

Fix the error in the shard allocation setting to specify primary shards count.

Elasticsearch

index.number_of_primary_shards: [1]

Drag options to blanks, or click blank then click option'

A"five"

Bfive

C"5"

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of a number

Writing the number as a word

The number of primary shards must be an integer, so 5 without quotes is correct.

4fill in blank

hard

Fill both blanks to create a dictionary mapping node names to shard counts.

Elasticsearch

shard_allocation = {"[1]": [2]

Drag options to blanks, or click blank then click option'

Anode_1

B5

C3

Dnode_2

Attempts:

3 left

💡 Hint

Common Mistakes

Using shard count as key

Using node name as a number

The dictionary key is the node name (a string without quotes here for code), and the value is the number of shards (an integer).

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension for shard sizes greater than 10GB.

Elasticsearch

large_shards = {node: size[1]2 for node, size in shard_sizes.items() if size [2] [3]

Drag options to blanks, or click blank then click option'

A*

B>

C10

D**

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of exponentiation

Using less than instead of greater than

Using 10 as a string instead of number

The code squares the size using **, then filters sizes greater than 10.

Practice

1. What is a node in Elasticsearch cluster architecture?

easy

A. A single machine that is part of the cluster

B. A group of machines working together

C. A piece of data stored in the index

D. A backup copy of data

Solution

1. Step 1: Understand the definition of a node

   A node is one machine or server that joins the Elasticsearch cluster to share work.

2. Step 2: Differentiate node from cluster and shard

   A cluster is many nodes working together; shards are parts of data inside nodes.

3. Final Answer:

   A single machine that is part of the cluster -> Option A

4. Quick Check:

   Node = single machine [OK]

Hint: Node means one machine in the cluster [OK]

Common Mistakes:

• Confusing node with cluster
• Thinking node is a data piece
• Mixing node with shard

2. Which of the following is the correct way to describe a shard in Elasticsearch?

easy

A. A part of an index that stores data

B. A node in the cluster

C. A full copy of the entire index

D. A cluster of nodes

Solution

1. Step 1: Define what a shard is

   A shard is a smaller piece or partition of an index that holds part of the data.

2. Step 2: Compare with other options

   It is not a full copy (that's a replica), not a node or cluster.

3. Final Answer:

   A part of an index that stores data -> Option A

4. Quick Check:

   Shard = index part [OK]

Hint: Shard means a data part of an index [OK]

Common Mistakes:

• Thinking shard is a full index copy
• Confusing shard with node
• Mixing shard with cluster

3. Consider an Elasticsearch cluster with 3 nodes and an index configured with 5 primary shards and 1 replica per shard. How many total shards will be in the cluster?

medium

A. 5 shards

B. 10 shards

C. 6 shards

D. 15 shards

Solution

1. Step 1: Calculate total shards per primary and replica

   Each primary shard has 1 replica, so total shards = primary shards + replicas = 5 + 5 = 10 shards.

2. Step 2: Understand shard distribution across nodes

   Since there are 3 nodes, shards are distributed but total shards remain 10. However, the question asks total shards in cluster, including replicas.

3. Step 3: Re-check options

   15 shards says 15 shards, which is incorrect. The correct total is 10 shards.

4. Final Answer:

   10 shards -> Option B

5. Quick Check:

   Total shards = primary + replica = 5 + 5 = 10 [OK]

Hint: Total shards = primary shards x (1 + replicas) [OK]

Common Mistakes:

• Counting only primary shards
• Adding nodes to shard count incorrectly
• Confusing replicas with nodes

4. You have an Elasticsearch cluster with 2 nodes and an index with 4 primary shards and 1 replica. You try to assign 2 replicas per shard. What is the problem with this configuration?

medium

A. Replicas must be zero for cluster to work

B. Primary shards must be equal to replica shards

C. Number of nodes must be equal to number of shards

D. You cannot have more replicas than nodes minus one

Solution

1. Step 1: Understand replica shard limits

   Replicas cannot exceed the number of nodes minus one because replicas cannot be on the same node as primary.

2. Step 2: Apply to given cluster

   With 2 nodes, max replicas per shard = 1 (2 - 1). Trying 2 replicas is invalid.

3. Final Answer:

   You cannot have more replicas than nodes minus one -> Option D

4. Quick Check:

   Replicas ≤ nodes - 1 [OK]

Hint: Replicas max = nodes minus one [OK]

Common Mistakes:

• Setting replicas more than nodes - 1
• Confusing primary and replica counts
• Assuming replicas can be zero always

5. You want to design an Elasticsearch cluster for high availability with 4 nodes. You plan to create an index with 6 primary shards and 2 replicas per shard. What is the best shard and replica configuration to avoid shard allocation errors?

hard

A. 6 primary shards and 3 replicas per shard, total 24 shards

B. 6 primary shards and 2 replicas per shard, total 18 shards

C. 6 primary shards and 1 replica per shard, total 12 shards

D. 4 primary shards and 2 replicas per shard, total 12 shards

Solution

1. Step 1: Check replica limit based on nodes

   With 4 nodes, max replicas per shard = nodes - 1 = 3. So 2 replicas is allowed.

2. Step 2: Consider shard allocation rules

   Each shard copy must be on a different node. 6 primary shards + 2 replicas = 18 shards total, but 18 shards on 4 nodes means some nodes hold multiple shards.

3. Step 3: Avoid allocation errors by balancing shards

   Too many shards per node can cause performance issues. 1 replica (total 12 shards) is safer and avoids errors.

4. Final Answer:

   6 primary shards and 1 replica per shard, total 12 shards -> Option C

5. Quick Check:

   Replicas ≤ nodes - 1 and balanced shards [OK]

Hint: Replicas max = nodes - 1; balance shards per node [OK]

Common Mistakes:

• Setting replicas more than nodes - 1
• Ignoring shard distribution limits
• Choosing fewer shards than needed