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.