Index aliases in Elasticsearch - Step-by-Step Execution

Concept Flow - Index aliases

Create Index

↓

Add Alias to Index

↓

Use Alias in Queries

↓

Alias Points to Index

↓

Switch Alias to Another Index

↓

Queries Use New Index via Alias

Create an index, assign an alias to it, use the alias in queries, then switch the alias to another index without changing queries.

Execution Sample

Elasticsearch

PUT /products_v1
PUT /_aliases
{
  "actions": [{ "add": { "index": "products_v1", "alias": "products" }}]
}

Create an index 'products_v1' and assign an alias 'products' to it.

Execution Table

Step	Action	Index State	Alias State	Result
1	Create index 'products_v1'	products_v1 created	No aliases	Index ready
2	Add alias 'products' to 'products_v1'	products_v1 exists	products -> products_v1	Alias added
3	Query using alias 'products'	products_v1 exists	products -> products_v1	Query runs on products_v1
4	Create index 'products_v2'	products_v1, products_v2 exist	products -> products_v1	New index ready
5	Switch alias 'products' to 'products_v2'	products_v1, products_v2 exist	products -> products_v2	Alias switched
6	Query using alias 'products'	products_v1, products_v2 exist	products -> products_v2	Query runs on products_v2
7	End	products_v1, products_v2 exist	products -> products_v2	Execution complete

💡 Alias switched to new index; queries now use 'products_v2'

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 5	Final
Index State	No indexes	products_v1	products_v1, products_v2	products_v1, products_v2	products_v1, products_v2
Alias 'products'	None	points to products_v1	points to products_v1	points to products_v2	points to products_v2

Key Moments - 2 Insights

Why does querying the alias 'products' not require changing the query after switching the alias?

Because the alias 'products' always points to one index at a time, switching the alias to a new index means queries using the alias automatically target the new index without query changes, as shown in steps 5 and 6.

Can an alias point to multiple indexes at once?

Yes, but in this example, the alias points to only one index at a time to simplify switching. This is shown in the Alias State column where 'products' points to a single index.

Visual Quiz - 3 Questions

Look at the execution table, after which step does the alias 'products' point to 'products_v2'?

A Step 3

B Step 5

C Step 4

D Step 6

💡 Hint

Check the 'Alias State' column in the execution table for step 5.

According to the variable tracker, what is the state of the alias 'products' after step 2?

A No alias assigned

B Points to products_v2

C Points to products_v1

D Points to both products_v1 and products_v2

💡 Hint

Look at the 'Alias 'products'' row after 'After Step 2' in variable_tracker.

If we add a new index but do not switch the alias, which index will queries using the alias target?

A The original index the alias points to

B Both indexes simultaneously

C The new index

D No index, query fails

💡 Hint

Refer to steps 4 and 6 in the execution table to see alias behavior.

Concept Snapshot

Index aliases let you create a friendly name for one or more indexes.
You can query the alias instead of the actual index name.
Switching the alias to a new index lets queries use the new data without changing query code.
Aliases can point to one or multiple indexes.
Use alias actions to add, remove, or switch aliases.

Full Transcript

This visual execution shows how Elasticsearch index aliases work. First, an index named 'products_v1' is created. Then, an alias 'products' is added to point to 'products_v1'. Queries use the alias 'products' to access data in 'products_v1'. Later, a new index 'products_v2' is created. The alias 'products' is switched to point to 'products_v2'. Queries using the alias now access 'products_v2' without changing the query. The variable tracker shows the alias state changing from pointing to 'products_v1' to 'products_v2'. Key moments clarify why queries don't need changes after alias switching and that aliases can point to multiple indexes but here point to one at a time. The quiz tests understanding of alias switching steps and alias state. The snapshot summarizes the main points about index aliases.

Practice

1.

What is the main purpose of using index aliases in Elasticsearch?

easy

A. To use simple names instead of real index names for easier access

B. To permanently rename an index

C. To delete multiple indexes at once

D. To backup indexes automatically

Solution

1. Step 1: Understand what index aliases do

   Index aliases provide a way to refer to one or more indexes using a simple name.

2. Step 2: Compare options with this purpose

   Only To use simple names instead of real index names for easier access describes using simple names instead of real index names, which matches the purpose of aliases.

3. Final Answer:

   To use simple names instead of real index names for easier access -> Option A

4. Quick Check:

   Index aliases simplify index names = D [OK]

Hint: Aliases are easy names for indexes, not permanent renames [OK]

Common Mistakes:

• Thinking aliases rename indexes permanently
• Confusing aliases with backup or delete functions
• Assuming aliases are only for single indexes

2.

Which of the following is the correct syntax to add an alias named logs_current to an index called logs_2024 using Elasticsearch API?

{
  "actions": [
    {
      "add": {
        "index": "logs_2024",
        "alias": "logs_current"
      }
    }
  ]
}

easy

A. PUT /logs_current { "index": "logs_2024" }

B. POST /_aliases { "actions": [{ "add": { "index": "logs_2024", "alias": "logs_current" } }] }

C. GET /logs_2024/_alias/logs_current

D. DELETE /_aliases { "actions": [{ "remove": { "index": "logs_2024", "alias": "logs_current" } }] }

Solution

1. Step 1: Identify the correct API endpoint and method

   Adding an alias uses POST on /_aliases with an actions array.

2. Step 2: Match the syntax with the options

   POST /_aliases { "actions": [{ "add": { "index": "logs_2024", "alias": "logs_current" } }] } correctly uses POST /_aliases with the add action and proper JSON structure.

3. Final Answer:

   POST /_aliases with add action JSON -> Option B

4. Quick Check:

   Adding alias uses POST /_aliases = A [OK]

Hint: Add aliases with POST /_aliases and actions array [OK]

Common Mistakes:

• Using PUT on alias name instead of POST on /_aliases
• Using GET to add an alias (GET is for reading)
• Confusing remove action with add

3.

Given these aliases and indexes:
logs_2023, logs_2024
Alias logs_all points to both indexes.
Which index will be searched when querying logs_all?

medium

A. Only logs_2023

B. Only logs_2024

C. No index, alias is invalid

D. Both logs_2023 and logs_2024

Solution

1. Step 1: Understand alias pointing to multiple indexes

   An alias can point to many indexes, so searching the alias searches all linked indexes.

2. Step 2: Apply to given alias logs_all

   Since logs_all points to both logs_2023 and logs_2024, queries to it search both indexes.

3. Final Answer:

   Both logs_2023 and logs_2024 -> Option D

4. Quick Check:

   Alias to multiple indexes searches all = C [OK]

Hint: Aliases can point to many indexes, searching all at once [OK]

Common Mistakes:

• Assuming alias searches only one index
• Thinking alias must be single index
• Believing alias is invalid if multiple indexes linked

4.

What is wrong with this alias update request?

{
  "actions": [
    {
      "add": {
        "alias": "current_logs",
        "index": "logs_2024"
      }
    },
    {
      "remove": {
        "alias": "old_logs",
        "index": "logs_2023"
      }
    }
  ]
}

Sent as POST to /_aliases.

medium

A. The request is correct and will work as expected

B. The JSON keys alias and index are swapped

C. The order of add and remove actions must be reversed

D. The HTTP method should be PUT, not POST

Solution

1. Step 1: Check JSON structure for alias actions

   The actions array correctly uses add and remove with keys alias and index in correct places.

2. Step 2: Verify HTTP method and endpoint

   POST to /_aliases is the correct way to update aliases.

3. Final Answer:

   The request is correct and will work as expected -> Option A

4. Quick Check:

   Correct alias update uses POST /_aliases with add/remove = A [OK]

Hint: POST /_aliases with add/remove actions is correct syntax [OK]

Common Mistakes:

• Thinking order of actions matters
• Swapping alias and index keys
• Using PUT instead of POST for alias updates

5.

You want to switch an alias active_logs from pointing to logs_2023 to logs_2024 without downtime. Which is the best approach?

hard

A. Remove alias from logs_2023 then add alias to logs_2024 in two separate requests

B. Delete logs_2023 index and then add alias to logs_2024

C. Use a single atomic alias update request with both remove and add actions

D. Create a new alias with a different name for logs_2024

Solution

1. Step 1: Understand alias switching without downtime

   Switching alias atomically avoids downtime by updating both remove and add in one request.

2. Step 2: Evaluate options for atomic update

   Use a single atomic alias update request with both remove and add actions uses a single request with remove and add actions, ensuring no downtime.

3. Final Answer:

   Use a single atomic alias update request with both remove and add actions -> Option C

4. Quick Check:

   Atomic alias update = remove + add in one request = B [OK]

Hint: Switch aliases atomically with one request to avoid downtime [OK]

Common Mistakes:

• Doing remove and add in separate requests causing downtime
• Deleting index instead of switching alias
• Creating new alias instead of switching existing one