Provisioner failure behavior in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens when a Terraform provisioner fails during resource creation?

Terraform marks the resource as tainted and stops the apply process unless you use the 'ignore_errors' option. This means the resource will be destroyed and recreated on the next apply.

intermediate

What is the purpose of the 'on_failure' argument in Terraform provisioners?

The 'on_failure' argument controls what Terraform does if the provisioner fails. Options include 'fail' (default), 'continue', and 'warn'.

intermediate

Explain the difference between 'fail' and 'continue' in the 'on_failure' setting.

'fail' stops the apply and marks the resource as tainted. 'continue' lets Terraform proceed even if the provisioner fails, without marking the resource as tainted.

advanced

How can you prevent Terraform from destroying a resource if a provisioner fails?

Set 'on_failure' to 'continue' or use 'ignore_errors = true' in the provisioner block to avoid resource destruction on failure.

beginner

Why should provisioners be used as a last resort in Terraform?

Provisioners can cause unpredictable failures and complicate resource management. It's better to use native Terraform resources or external configuration management tools.

What does Terraform do by default if a provisioner fails?

A Stops apply and marks resource as tainted

B Ignores the failure and continues

C Automatically retries the provisioner

D Deletes the entire Terraform state

By default, Terraform stops the apply and marks the resource as tainted when a provisioner fails.

Which 'on_failure' option allows Terraform to continue even if the provisioner fails?

A fail

B continue

C warn

D ignore

'continue' lets Terraform proceed without marking the resource as tainted.

What is the effect of setting 'ignore_errors = true' in a provisioner?

A Terraform ignores provisioner failures and continues

B Terraform pauses the apply process

C Terraform deletes the resource immediately

D Terraform will retry the provisioner indefinitely

'ignore_errors = true' tells Terraform to ignore failures and continue the apply.

Why is it recommended to minimize the use of provisioners in Terraform?

A They are deprecated and no longer supported

B They increase the cost of cloud resources

C They can cause unpredictable failures and complexity

D They slow down Terraform plan operations

Provisioners can cause unpredictable failures and make resource management harder.

If a provisioner fails and 'on_failure' is set to 'warn', what happens?

A Terraform retries the provisioner

B Terraform stops and marks resource as tainted

C Terraform ignores the failure silently

D Terraform continues but logs a warning

'warn' lets Terraform continue but logs a warning about the failure.

Describe how Terraform handles provisioner failures and the options to control this behavior.

Think about what happens when a script run by Terraform fails and how you can tell Terraform to react differently.

Explain why relying on provisioners in Terraform can be risky and what alternatives exist.

Consider how you would manage configuration without running scripts inside Terraform.

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