Index lifecycle management in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this ILM policy status query?

Given an index named logs-2023.06 managed by an ILM policy, what will be the phase shown in the output after the index has been rolled over and is currently in the warm phase?

Elasticsearch

GET logs-2023.06/_ilm/explain

A {"indices":{"logs-2023.06":{"index":"logs-2023.06","managed":true,"policy":"logs_policy","phase":"warm","action":"complete","step":"complete"}}}

B {"indices":{"logs-2023.06":{"index":"logs-2023.06","managed":true,"policy":"logs_policy","phase":"hot","action":"rollover","step":"check-rollover-ready"}}}

C {"indices":{"logs-2023.06":{"index":"logs-2023.06","managed":true,"policy":"logs_policy","phase":"delete","action":"wait-for-shard-history-leases","step":"wait-for-shard-history-leases"}}}

D {"indices":{"logs-2023.06":{"index":"logs-2023.06","managed":false}}}

💡 Hint

Think about what phase comes after rollover in a typical ILM policy.

After rollover, the index moves from the hot phase to the warm phase. The ILM explain API shows the current phase and step for the index.

🧠 Conceptual

intermediate

Which ILM phase is best for reducing index shard size without deleting data?

In Index Lifecycle Management, which phase is typically used to reduce shard size by shrinking or force merging indices, while keeping the data available?

A Cold phase

B Warm phase

C Hot phase

D Delete phase

💡 Hint

This phase is after hot and before cold, focusing on optimizing storage.

The warm phase is used to optimize indices by shrinking or force merging to reduce shard size while keeping data accessible.

📝 Syntax

advanced

Which ILM policy JSON snippet correctly defines a delete phase after 30 days?

Select the correct JSON snippet that defines a delete phase in an ILM policy to delete indices after 30 days.

A { "delete": { "min_age": "30d", "actions": { "remove": {} } } }

B { "delete": { "min_age": 30, "actions": { "delete": {} } } }

C { "delete": { "min_age": "30", "actions": { "remove": {} } } }

D { "delete": { "min_age": "30d", "actions": { "delete": {} } } }

💡 Hint

The min_age must be a string with time unit, and the action to delete is named 'delete'.

The correct syntax uses a string with 'd' for days and the action key 'delete' to remove indices.

❓ optimization

advanced

How to optimize ILM policy to reduce disk usage quickly after rollover?

You want to reduce disk usage as soon as possible after rollover. Which ILM phase action should you add immediately after rollover to optimize storage?

A Add a force_merge action in the warm phase

B Add a shrink action in the hot phase

C Add a freeze action in the cold phase

D Add a delete action in the warm phase

💡 Hint

Force merge reduces segment count and disk usage without deleting data.

Force merge in the warm phase reduces disk usage by merging index segments after rollover.

🔧 Debug

expert

Why does this ILM policy fail to delete indices after 30 days?

An ILM policy has this delete phase snippet: { "delete": { "min_age": "30d", "actions": { "remove": {} } } } Why does the index not get deleted after 30 days?

A The min_age should be an integer, not a string.

B The delete phase must be named 'delete_phase', not 'delete'.

C The action 'remove' is invalid; it should be 'delete'.

D The policy must include a rollover action before delete.

💡 Hint

Check the action names supported by ILM for deleting indices.

The correct action to delete indices is 'delete', not 'remove'. Using 'remove' causes the delete phase to be ignored.

Practice

1. What is the main purpose of Index Lifecycle Management (ILM) in Elasticsearch?

easy

A. To automate index handling and improve cluster performance

B. To manually create indexes for each data type

C. To backup data to external storage

D. To encrypt index data for security

Solution

1. Step 1: Understand ILM's role

   ILM automates managing indexes through their lifecycle phases.

2. Step 2: Identify the benefit

   Automation helps save space and improves cluster health and performance.

3. Final Answer:

   To automate index handling and improve cluster performance -> Option A

4. Quick Check:

   ILM automates index management = A [OK]

Hint: ILM automates index tasks to keep Elasticsearch healthy [OK]

Common Mistakes:

• Thinking ILM is for manual index creation
• Confusing ILM with backup or encryption
• Assuming ILM only deletes indexes

2. Which of the following is the correct way to define a rollover action in an ILM policy JSON?

easy

A. "rollover": { "max_size": "50gb", "max_age": "30d" }

B. "rollover": "true"

C. "rollover": { "size": "50gb" }

D. "rollover": { "max_documents": 1000 }

Solution

1. Step 1: Check rollover action syntax

   Rollover requires conditions like max_size and max_age in a JSON object.

2. Step 2: Validate options

   "rollover": { "max_size": "50gb", "max_age": "30d" } correctly uses max_size and max_age keys with proper values.

3. Final Answer:

   "rollover": { "max_size": "50gb", "max_age": "30d" } -> Option A

4. Quick Check:

   Rollover needs max_size and max_age keys = A [OK]

Hint: Rollover needs max_size and max_age keys in JSON [OK]

Common Mistakes:

• Using string 'true' instead of object for rollover
• Missing max_age or max_size keys
• Using incorrect key names like 'size'

3. Given this ILM policy snippet:

{"phases": {"hot": {"actions": {"rollover": {"max_size": "10gb"}}}, "delete": {"min_age": "90d", "actions": {"delete": {}}}}}

What happens to an index after it reaches 10GB?

medium

A. It archives data to external storage

B. It rolls over to a new index and continues indexing

C. It stops accepting new data but stays

D. It is immediately deleted

Solution

1. Step 1: Analyze rollover action in hot phase

   The policy rolls over the index when it reaches 10GB.

2. Step 2: Understand delete phase timing

   Deletion happens only after 90 days, so not immediate.

3. Final Answer:

   It rolls over to a new index and continues indexing -> Option B

4. Quick Check:

   Rollover at 10GB, delete after 90d = D [OK]

Hint: Rollover triggers at size, delete waits min_age [OK]

Common Mistakes:

• Confusing rollover with immediate deletion
• Ignoring min_age delay for delete phase
• Assuming data stops indexing after rollover

4. You have this ILM policy JSON:

{"phases": {"hot": {"actions": {"rollover": {"max_size": "20gb"}}}, "warm": {"min_age": "10d", "actions": {"shrink": {"number_of_shards": 1}}}}}

After applying, the shrink action never runs. What is the likely cause?

medium

A. Rollover max_size is too small

B. Shrink action requires delete phase

C. Shrink action must be in hot phase

D. The index has not reached 10 days old yet

Solution

1. Step 1: Check warm phase min_age

   Shrink runs only after index is at least 10 days old.

2. Step 2: Confirm index age

   If index age is less than 10 days, shrink won't trigger yet.

3. Final Answer:

   The index has not reached 10 days old yet -> Option D

4. Quick Check:

   min_age controls action timing = C [OK]

Hint: Check min_age before expecting warm phase actions [OK]

Common Mistakes:

• Assuming shrink needs delete phase
• Changing rollover size unrelated to shrink
• Placing shrink in wrong phase

5. You want to create an ILM policy that:
- Rolls over an index at 30GB or 15 days
- Moves the index to warm phase after rollover
- Deletes the index 60 days after rollover

Which policy configuration correctly implements this?

hard

A. {"phases": {"hot": {"actions": {"rollover": {"max_size": "30gb"}}}, "warm": {"min_age": "30d", "actions": {}}, "delete": {"min_age": "60d", "actions": {"delete": {}}}}}

B. {"phases": {"hot": {"actions": {"rollover": {"max_age": "15d"}}}, "warm": {"min_age": "15d", "actions": {"shrink": {}}}, "delete": {"min_age": "60d", "actions": {"delete": {}}}}}

C. {"phases": {"hot": {"actions": {"rollover": {"max_size": "30gb", "max_age": "15d"}}}, "warm": {"min_age": "15d", "actions": {}}, "delete": {"min_age": "60d", "actions": {"delete": {}}}}}

D. {"phases": {"hot": {"actions": {"rollover": {"max_size": "15gb", "max_age": "30d"}}}, "warm": {"min_age": "15d", "actions": {}}, "delete": {"min_age": "60d", "actions": {"delete": {}}}}}

Solution

1. Step 1: Verify rollover conditions

   {"phases": {"hot": {"actions": {"rollover": {"max_size": "30gb", "max_age": "15d"}}}, "warm": {"min_age": "15d", "actions": {}}, "delete": {"min_age": "60d", "actions": {"delete": {}}}}} uses max_size 30gb and max_age 15d, matching requirements.

2. Step 2: Check warm and delete phases

   Warm phase starts at 15d (after rollover), delete at 60d, as required.

3. Step 3: Confirm other options

   Other options have wrong sizes, ages, or missing actions.

4. Final Answer:

   {"phases": {"hot": {"actions": {"rollover": {"max_size": "30gb", "max_age": "15d"}}}, "warm": {"min_age": "15d", "actions": {}}, "delete": {"min_age": "60d", "actions": {"delete": {}}}}} -> Option C

5. Quick Check:

   Rollover at 30gb/15d, warm at 15d, delete at 60d = B [OK]

Hint: Match rollover size and age, then warm and delete min_age [OK]

Common Mistakes:

• Swapping max_size and max_age values
• Setting warm min_age too late
• Missing delete action or wrong min_age