Index aliases in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this alias query?

Given an Elasticsearch index alias products_current pointing to the index products_2024, what will the following query return?

{"query": {"match_all": {}}}

when executed on the alias products_current?

Elasticsearch

GET /products_current/_search
{
  "query": {
    "match_all": {}
  }
}

A Returns an error because the alias name is invalid

B Returns no documents because aliases cannot be queried directly

C Returns documents only if the alias has a filter defined

D Returns all documents from the index products_2024

💡 Hint

Think about what an alias does in Elasticsearch.

An alias in Elasticsearch acts as a pointer to one or more indices. Querying an alias is equivalent to querying the underlying index or indices it points to. Since products_current points to products_2024, the query returns all documents from that index.

🧠 Conceptual

intermediate

How does an alias with a filter affect search results?

If an alias active_users points to the index users with a filter {"term": {"status": "active"}}, what will a search on active_users return?

A All documents in the <code>users</code> index regardless of status

B No documents because filters on aliases are ignored

C Only documents where the field <code>status</code> is <code>active</code>

D An error because filters cannot be applied on aliases

💡 Hint

Consider how alias filters limit visible documents.

Alias filters restrict the documents visible through that alias. Searching the alias active_users returns only documents matching the filter, i.e., where status is active.

📝 Syntax

advanced

Which option correctly creates an alias with a filter?

Choose the correct JSON syntax to create an alias recent_orders for the index orders that only shows documents where order_date is after 2024-01-01.

Elasticsearch

PUT /orders/_alias/recent_orders
{
  "filter": {
    "range": {
      "order_date": {
        "gt": "2024-01-01"
      }
    }
  }
}

A { "filter": { "range": { "order_date": { "gt": "2024-01-01" } } } }

B { "query": { "range": { "order_date": { "gt": "2024-01-01" } } } }

C { "filter": { "term": { "order_date": "2024-01-01" } } }

D { "alias": { "filter": { "range": { "order_date": { "gte": "2024-01-01" } } } } }

💡 Hint

Alias filters use the filter key, not query.

The correct syntax uses the filter key with a range query. Option A matches the correct structure. Option A uses query which is invalid for alias filters. Option A uses term which does not specify a range. Option A has an invalid alias wrapper.

❓ optimization

advanced

Why use aliases for zero-downtime reindexing?

You want to update your Elasticsearch index products_v1 to products_v2 without downtime. How do aliases help?

A Aliases cannot help with zero-downtime reindexing

B Point the alias <code>products</code> to <code>products_v2</code> after reindexing, so clients query the alias without changing code

C Use aliases to merge both indices into one automatically

D Delete <code>products_v1</code> and rename <code>products_v2</code> to <code>products_v1</code> directly

💡 Hint

Think about how aliases abstract index names.

Aliases allow you to switch the pointer from the old index to the new index instantly. Clients query the alias name, so no code changes are needed. This enables zero downtime during reindexing.

🔧 Debug

expert

Why does this alias creation fail?

You run this command to create an alias with a filter:

PUT /logs/_alias/error_logs
{
  "filter": {
    "term": {
      "level": "error"
    }
  },
  "routing": "error"
}

But you get an error. What is the cause?

A The alias creation fails because <code>routing</code> is not allowed with <code>filter</code>

B The alias creation fails because <code>routing</code> must be a number, not a string

C The alias creation fails because <code>routing</code> must be inside <code>filter</code>

D The alias creation fails because the <code>term</code> filter syntax is incorrect

💡 Hint

Check Elasticsearch alias API rules for routing and filter.

Elasticsearch does not allow setting routing and filter together in the same alias definition. You must choose one or create separate aliases.