Ingest pipelines in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this ingest pipeline simulation?

Given the following ingest pipeline configuration and a document, what will be the value of the full_name field after processing?

Elasticsearch

{
  "description": "Combine first and last name",
  "processors": [
    {
      "set": {
        "field": "full_name",
        "value": "{{first_name}} {{last_name}}"
      }
    }
  ]
}

Document:
{
  "first_name": "Alice",
  "last_name": "Johnson"
}

A "full_name" will be "Alice"

B "full_name" will be "{{first_name}} {{last_name}}" (literal string)

C The pipeline will fail with a template error

D "full_name" will be "Alice Johnson"

💡 Hint

Remember that double curly braces {{}} are used for variable substitution in ingest pipelines.

The set processor uses mustache templates to replace variables with their values from the document. So {{first_name}} and {{last_name}} are replaced by "Alice" and "Johnson" respectively, resulting in "Alice Johnson".

❓ Predict Output

intermediate

What is the output of this pipeline with a grok processor?

Given this ingest pipeline and input document, what will be the value of the status_code field after processing?

Elasticsearch

{
  "description": "Extract status code from message",
  "processors": [
    {
      "grok": {
        "field": "message",
        "patterns": ["%{WORD:method} %{URIPATHPARAM:request} %{NUMBER:status_code:int}"]
      }
    }
  ]
}

Document:
{
  "message": "GET /home 404"
}

A 404 (as an integer)

B "404" (as a string)

C null (field not extracted)

D Pipeline fails with grok parse error

💡 Hint

The grok pattern uses :int to convert the extracted value to integer.

The grok processor extracts the status code from the message field and converts it to an integer because of the :int suffix in the pattern.

🔧 Debug

advanced

Why does this pipeline fail with a 'field not found' error?

This ingest pipeline uses a rename processor but fails with an error. What is the cause?

Elasticsearch

{
  "description": "Rename field",
  "processors": [
    {
      "rename": {
        "field": "user",
        "target_field": "username"
      }
    }
  ]
}

Document:
{
  "username": "bob123"
}

A The rename processor requires a 'copy' flag to be set to true.

B The source field 'user' does not exist in the document, causing the error.

C The pipeline syntax is invalid because 'field' and 'target_field' are swapped.

D The target field 'username' already exists, causing a conflict error.

💡 Hint

Check if the source field exists in the input document.

The rename processor tries to rename a field that does not exist in the document. Since 'user' is missing, the processor fails with a 'field not found' error.

📝 Syntax

advanced

Which option shows a valid ingest pipeline with a conditional processor?

Select the pipeline JSON that correctly uses a condition to run a processor only if the field status equals error.

A

{
  "processors": [
    {
      "set": {
        "field": "alert",
        "value": "true",
        "if": "ctx.status == 'error'"
      }
    }
  ]
}

B

{
  "processors": [
    {
      "set": {
        "field": "alert",
        "value": "true",
        "condition": "ctx.status == 'error'"
      }
    }
  ]
}

C

{
  "processors": [
    {
      "set": {
        "field": "alert",
        "value": "true"
      },
      "if": "ctx.status == 'error'"
    }
  ]
}

D

{
  "processors": [
    {
      "set": {
        "field": "alert",
        "value": "true"
      },
      "condition": "ctx.status == 'error'"
    }
  ]
}

💡 Hint

The condition must be outside the processor object, not inside the processor's parameters.

In ingest pipelines, the condition is specified as a sibling key to the processor type, not inside the processor's parameters. So 'if' is correct and placed outside the 'set' object.

🚀 Application

expert

How many processors run for this document in the pipeline?

Consider this pipeline with two processors and a condition on the second. How many processors will run when processing the document below?

Elasticsearch

{
  "processors": [
    {
      "set": {
        "field": "processed",
        "value": true
      }
    },
    {
      "remove": {
        "field": "debug"
      },
      "if": "ctx.debug == false"
    }
  ]
}

Document:
{
  "debug": true
}

A Only 1 processor runs (the set processor).

B Both processors run.

C No processors run because condition fails.

D Only the remove processor runs.

💡 Hint

Check the condition on the remove processor and the value of the debug field.

The first processor always runs and sets 'processed' to true. The second processor runs only if ctx.debug == false, but debug is true, so it does not run.

Practice

1. What is the main purpose of an ingest pipeline in Elasticsearch?

easy

A. To create visualizations from data

B. To query documents faster

C. To backup Elasticsearch data

D. To modify documents before they are indexed

Solution

1. Step 1: Understand ingest pipeline role

   An ingest pipeline processes documents before they are stored in Elasticsearch.

2. Step 2: Compare options to pipeline purpose

   Only To modify documents before they are indexed matches this role; others describe unrelated tasks.

3. Final Answer:

   To modify documents before they are indexed -> Option D

4. Quick Check:

   Ingest pipeline = modify before indexing [OK]

Hint: Ingest pipelines change data before saving [OK]

Common Mistakes:

• Confusing pipelines with query optimization
• Thinking pipelines create backups
• Assuming pipelines generate reports

2. Which of the following is the correct way to define a processor that adds a field "source": "web" in an ingest pipeline?

easy

A. "processors": [{"add": {"field": "source", "value": "web"}}]

B. "processors": [{"remove": {"field": "source", "value": "web"}}]

C. "processors": [{"set": {"field": "source", "value": "web"}}]

D. "processors": [{"append": {"field": "source", "value": "web"}}]

Solution

1. Step 1: Identify processor to add or set field

   The set processor assigns or adds a field with a value.

2. Step 2: Check syntax correctness

   "processors": [{"set": {"field": "source", "value": "web"}}] uses set with correct JSON structure; add is not a valid processor name.

3. Final Answer:

   "processors": [{"set": {"field": "source", "value": "web"}}] -> Option C

4. Quick Check:

   Use set to add fields [OK]

Hint: Use 'set' processor to add or update fields [OK]

Common Mistakes:

• Using 'add' instead of 'set' processor
• Confusing 'append' with adding new fields
• Trying to remove field when adding

3. Given this ingest pipeline snippet:

{"processors": [{"rename": {"field": "old_name", "target_field": "new_name"}}]}

What happens to a document {"old_name": "value"} when processed?

medium

A. {"old_name": "value", "new_name": "value"}

B. {"new_name": "value"}

C. {"old_name": null}

D. {"old_name": "value"}

Solution

1. Step 1: Understand rename processor effect

   The rename processor moves the value from old_name to new_name, removing the original field.

2. Step 2: Apply to example document

   Input {"old_name": "value"} becomes {"new_name": "value"} after processing.

3. Final Answer:

   {"new_name": "value"} -> Option B

4. Quick Check:

   Rename moves field, removes old [OK]

Hint: Rename moves field value, deletes old field [OK]

Common Mistakes:

• Thinking rename duplicates field
• Assuming old field remains
• Confusing rename with copy

4. You wrote this pipeline processor:

{"processors": [{"convert": {"field": "age", "type": "integer"}}]}

But when simulating, you get an error. What is the likely cause?

medium

A. The field "age" does not exist in the document

B. The "convert" processor does not exist

C. The "type" value "integer" is invalid

D. The pipeline must have a "description" field

Solution

1. Step 1: Check processor and type validity

   The "convert" processor and type "integer" are valid in Elasticsearch ingest pipelines.

2. Step 2: Identify common error cause

   If the field "age" is missing in the document, conversion fails causing error during simulation.

3. Final Answer:

   The field "age" does not exist in the document -> Option A

4. Quick Check:

   Missing field causes convert error [OK]

Hint: Convert errors if field missing in document [OK]

Common Mistakes:

• Assuming convert processor is invalid
• Thinking 'integer' is wrong type
• Believing description is mandatory

5. You want to create an ingest pipeline that adds a field "status": "new" only if the field "priority" exists. Which processor setup achieves this?

hard

A. "processors": [{"set": {"field": "status", "value": "new", "if": "ctx.priority != null"}}]

B. "processors": [{"set": {"field": "status", "value": "new"}}, {"exists": {"field": "priority"}}]

C. "processors": [{"conditional": {"field": "priority", "processor": {"set": {"field": "status", "value": "new"}}}}]

D. "processors": [{"set": {"field": "status", "value": "new"}, "condition": "priority"}]

Solution

1. Step 1: Understand conditional execution in pipelines

   Processors support an "if" condition using painless scripts to run only when true.

2. Step 2: Identify correct syntax for conditional set

   "processors": [{"set": {"field": "status", "value": "new", "if": "ctx.priority != null"}}] uses "if": "ctx.priority != null" which runs set only if "priority" exists.

3. Final Answer:

   "processors": [{"set": {"field": "status", "value": "new", "if": "ctx.priority != null"}}] -> Option A

4. Quick Check:

   Use "if" with painless script for conditions [OK]

Hint: Use 'if' with painless script to conditionally run processor [OK]

Common Mistakes:

• Using non-existent 'conditional' processor
• Placing condition outside processor block
• Misusing 'exists' as processor