Provisioner failure behavior in Terraform - Mini Project: Build & Apply

Provisioner Failure Behavior in Terraform

📖 Scenario: You are managing cloud infrastructure using Terraform. Sometimes, when Terraform runs a provisioner script on a resource, the script might fail. You want to control what happens when this failure occurs.Terraform allows you to specify how it should behave if a provisioner fails, using the on_failure setting.

🎯 Goal: Build a Terraform configuration that creates a simple resource with a local-exec provisioner. Configure the provisioner to handle failure by choosing the on_failure behavior.You will create the resource, add the provisioner, and set the failure behavior to continue.

📋 What You'll Learn

Create a Terraform resource of type null_resource named example

Add a local-exec provisioner that runs the command exit 1 (which will fail)

Add the on_failure argument to the provisioner and set it to continue

💡 Why This Matters

🌍 Real World

In real cloud infrastructure, provisioners run scripts or commands on resources after creation. Sometimes these scripts fail, and you need to decide if Terraform should stop or continue.

💼 Career

Understanding provisioner failure behavior helps cloud engineers manage infrastructure deployments reliably and avoid unexpected interruptions.

1

Create a null_resource named example

Create a Terraform resource block for null_resource named example.

Terraform

# Your code here

Hint

The resource block starts with resource "null_resource" "example" { and ends with }.

2

Add a local-exec provisioner with a failing command

Inside the null_resource named example, add a provisioner block of type local-exec that runs the command exit 1.

Terraform

resource "null_resource" "example" {
  # Add local-exec provisioner here
}

Hint

The provisioner block should have command = "exit 1" inside.

3

Add on_failure behavior to continue on failure

Inside the local-exec provisioner block, add the argument on_failure and set it to continue.

Terraform

resource "null_resource" "example" {
  provisioner "local-exec" {
    command = "exit 1"
    # Add on_failure = "continue" here
  }
}

Hint

The on_failure argument controls what happens if the provisioner fails.

4

Complete the Terraform configuration

Ensure the Terraform configuration has the null_resource named example with a local-exec provisioner running exit 1 and on_failure = "continue" set.

Terraform

resource "null_resource" "example" {
  provisioner "local-exec" {
    command = "exit 1"
    on_failure = "continue"
  }
}
# Configuration complete

Hint

Review the full resource block to confirm all parts are present.

Practice

1.

What does the on_failure argument in a Terraform provisioner control?

easy

A. It controls what happens if the provisioner script or command fails.

B. It sets the timeout duration for the provisioner execution.

C. It defines the order in which provisioners run.

D. It specifies the operating system for the provisioner.

Solution

1. Step 1: Understand provisioner purpose

   Provisioners run scripts or commands after resource creation.

2. Step 2: Role of on_failure

   The on_failure argument controls what Terraform does if the provisioner fails.

3. Final Answer:

   It controls what happens if the provisioner script or command fails. -> Option A

4. Quick Check:

   on_failure controls failure behavior [OK]

Hint: Remember: on_failure decides action on provisioner failure [OK]

Common Mistakes:

• Confusing on_failure with timeout settings
• Thinking on_failure sets provisioner order
• Assuming on_failure defines OS type

2.

Which of the following is the correct syntax to make a provisioner continue even if it fails?

provisioner "local-exec" {
  command = "echo Hello"
  on_failure = ?
}

easy

A. "continue"

B. "fail"

C. "ignore"

D. "skip"

Solution

1. Step 1: Recall valid on_failure values

   Terraform supports fail and continue as valid on_failure values.

2. Step 2: Identify correct value to continue on failure

   To continue even if the provisioner fails, use continue.

3. Final Answer:

   "continue" -> Option A

4. Quick Check:

   on_failure = "continue" continues on failure [OK]

Hint: Use "continue" to ignore failure and proceed [OK]

Common Mistakes:

• Using invalid values like "ignore" or "skip"
• Confusing "fail" with continuing on failure
• Omitting quotes around the value

3.

Given this Terraform snippet, what happens if the local-exec provisioner command fails?

resource "null_resource" "example" {
  provisioner "local-exec" {
    command = "exit 1"
    on_failure = "fail"
  }
}

medium

A. Terraform retries the provisioner command automatically.

B. Terraform ignores the failure and continues applying other resources.

C. Terraform stops and reports an error, halting the apply process.

D. Terraform logs a warning but marks the resource as created.

Solution

1. Step 1: Analyze provisioner command and on_failure

   The command "exit 1" will fail. The on_failure is set to "fail".

2. Step 2: Understand effect of on_failure = "fail"

   This setting causes Terraform to stop and report an error if the provisioner fails.

3. Final Answer:

   Terraform stops and reports an error, halting the apply process. -> Option C

4. Quick Check:

   on_failure = "fail" stops on failure [OK]

Hint: Fail stops Terraform; continue lets it proceed [OK]

Common Mistakes:

• Assuming Terraform retries automatically
• Thinking failure is ignored with "fail"
• Believing resource is created despite failure

4.

Identify the error in this provisioner block that causes Terraform to ignore failures unexpectedly:

provisioner "remote-exec" {
  inline = ["false_command"]
  on_failure = fail
}

medium

A. The on_failure argument is not allowed in provisioners.

B. The on_failure value should be a string with quotes.

C. The provisioner type remote-exec is not supported.

D. The inline command is invalid and causes syntax error.

Solution

1. Step 1: Check on_failure syntax

   The value for on_failure must be a quoted string, e.g., "fail" or "continue".

2. Step 2: Identify impact of missing quotes

   Without quotes, Terraform treats it as an identifier, causing unexpected behavior or ignoring the setting.

3. Final Answer:

   The on_failure value should be a string with quotes. -> Option B

4. Quick Check:

   on_failure values require quotes [OK]

Hint: Always quote on_failure values "fail" or "continue" [OK]

Common Mistakes:

• Omitting quotes around on_failure values
• Confusing command errors with syntax errors
• Thinking on_failure is unsupported

5.

You want to run a local-exec provisioner that might fail but should not stop Terraform from creating other resources. Which configuration achieves this?

resource "null_resource" "example" {
  provisioner "local-exec" {
    command = "some_command"
    on_failure = ?
  }
}

hard

A. "fail" to stop on failure

B. "retry" to try again on failure

C. "ignore" to silently skip failure

D. "continue" to ignore failure and proceed

Solution

1. Step 1: Understand requirement to not stop Terraform

   The provisioner may fail but Terraform should continue creating other resources.

2. Step 2: Choose correct on_failure value

   Using on_failure = "continue" tells Terraform to ignore provisioner failure and proceed.

3. Final Answer:

   "continue" to ignore failure and proceed -> Option D

4. Quick Check:

   on_failure = "continue" allows continuation on failure [OK]

Hint: Use "continue" to keep going despite provisioner failure [OK]

Common Mistakes:

• Using unsupported values like "retry" or "ignore"
• Choosing "fail" which stops Terraform
• Not quoting the on_failure value