Local-exec provisioner in Terraform - Step-by-Step Execution

Process Flow - Local-exec provisioner

Terraform plan starts

↓

Resource created

↓

Local-exec provisioner triggers

↓

Runs local command/script

↓

Command success?

No→Error stops apply

Yes↓

Terraform apply continues/completes

Terraform creates a resource, then runs a local command on your machine using local-exec provisioner. If the command fails, apply stops.

Execution Sample

Terraform

resource "null_resource" "example" {
  provisioner "local-exec" {
    command = "echo Hello from local-exec"
  }
}

Creates a dummy resource and runs a local shell command printing a message on your machine.

Process Table

Step	Action	Resource State	Provisioner Command	Command Result	Next Step
1	Start terraform apply	No resource	N/A	N/A	Create resource
2	Create null_resource.example	Resource created	N/A	N/A	Run local-exec provisioner
3	Run local-exec command	Resource created	echo Hello from local-exec	Hello from local-exec printed	Check command success
4	Check command success	Resource created	N/A	Success	Complete apply
5	Terraform apply completes	Resource created	N/A	N/A	End

💡 Local-exec command succeeded, so terraform apply completes successfully.

Status Tracker

Variable	Start	After Step 2	After Step 3	Final
Resource State	No resource	Resource created	Resource created	Resource created
Provisioner Command	N/A	N/A	echo Hello from local-exec	N/A
Command Result	N/A	N/A	Hello from local-exec printed	Success

Key Moments - 3 Insights

Why does terraform stop if the local-exec command fails?

Terraform treats the local-exec provisioner as part of resource creation. If the command fails (see step 4 in execution_table), terraform stops to avoid inconsistent state.

Does the local-exec command run on the cloud resource?

No, local-exec runs on your local machine where terraform runs, not on the cloud resource itself (step 3 in execution_table).

Can local-exec provisioner access resource attributes?

Yes, you can use resource attributes in the command string, but the command still runs locally (noted in step 3).

Visual Quiz - 3 Questions

Look at the execution_table, what is the resource state after step 2?

A Resource created

B No resource

C Resource deleted

D Resource failed

💡 Hint

Check the 'Resource State' column at step 2 in execution_table.

At which step does the local-exec command run?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look for 'Run local-exec command' in the 'Action' column in execution_table.

If the local-exec command fails, what happens to terraform apply?

A It retries the command infinitely

B It stops with an error

C It continues normally

D It ignores the failure and completes

💡 Hint

Refer to the concept_flow and key_moments about command failure stopping apply.

Concept Snapshot

Local-exec provisioner runs a command on your local machine after resource creation.
Syntax: provisioner "local-exec" { command = "your-command" }
Runs during terraform apply.
If command fails, terraform apply stops.
Useful for local scripts or notifications.

Full Transcript

The local-exec provisioner in terraform runs a command on your local machine after a resource is created. The flow starts with terraform creating the resource, then triggering the local-exec provisioner to run the specified command. If the command succeeds, terraform continues and completes the apply. If it fails, terraform stops to avoid inconsistent state. The command runs locally, not on the cloud resource. You can use resource attributes in the command string. This provisioner is useful for running local scripts or notifications during terraform apply.

Practice

1. What does the local-exec provisioner do in Terraform?

easy

A. Runs commands inside the cloud resource

B. Executes Terraform plan without applying changes

C. Creates a local copy of the Terraform state file

D. Runs commands on your local machine after resource creation

Solution

1. Step 1: Understand provisioner types

   Terraform provisioners run scripts or commands either locally or remotely after resource creation.

2. Step 2: Identify local-exec purpose

   The local-exec provisioner specifically runs commands on your local machine, not inside the cloud resource.

3. Final Answer:

   Runs commands on your local machine after resource creation -> Option D

4. Quick Check:

   local-exec runs commands locally [OK]

Hint: Local-exec runs commands on your own computer [OK]

Common Mistakes:

• Confusing local-exec with remote-exec
• Thinking it runs inside the cloud resource
• Assuming it manages Terraform state files

2. Which of the following is the correct syntax to use a local-exec provisioner in a Terraform resource?

easy

A. provisioner "local-exec" { command = "echo Hello" }

B. provisioner local-exec { run = "echo Hello" }

C. local_exec { command = "echo Hello" }

D. provisioner "local_exec" { execute = "echo Hello" }

Solution

1. Step 1: Recall Terraform provisioner syntax

   Provisioners use the keyword provisioner followed by the provisioner type in quotes.

2. Step 2: Check correct attribute names

   The local-exec provisioner uses command to specify the shell command to run.

3. Final Answer:

   provisioner "local-exec" { command = "echo Hello" } -> Option A

4. Quick Check:

   Correct syntax uses provisioner "local-exec" and command [OK]

Hint: Use quotes and 'command' attribute for local-exec [OK]

Common Mistakes:

• Omitting quotes around local-exec
• Using wrong attribute names like run or execute
• Using underscore instead of dash in local-exec

3. Given this Terraform snippet, what will happen when the resource is created?

resource "null_resource" "example" {
  provisioner "local-exec" {
    command = "echo Resource created"
  }
}

medium

A. Terraform will fail because null_resource cannot have provisioners

B. Terraform will print 'Resource created' inside the cloud resource

C. Terraform will print 'Resource created' on your local machine

D. Terraform will ignore the provisioner and create the resource silently

Solution

1. Step 1: Understand null_resource and local-exec

   The null_resource is a Terraform resource that supports provisioners for running commands.

2. Step 2: Analyze the command execution

   The local-exec provisioner runs the command on your local machine, so it will print the message locally.

3. Final Answer:

   Terraform will print 'Resource created' on your local machine -> Option C

4. Quick Check:

   local-exec runs commands locally, so output appears locally [OK]

Hint: local-exec runs commands locally, not remotely [OK]

Common Mistakes:

• Thinking output appears inside cloud resource
• Believing null_resource disallows provisioners
• Assuming provisioners are ignored silently

4. You wrote this Terraform code but get an error when applying:

resource "null_resource" "fail_example" {
  provisioner "local-exec" {
    command = echo "Hello"
  }
}

What is the cause of the error?

medium

A. Missing quotes around the command string

B. local-exec provisioner cannot be used with null_resource

C. The command attribute should be named run

D. Terraform does not support echo commands

Solution

1. Step 1: Check command syntax

   The command value must be a string enclosed in quotes in Terraform configuration.

2. Step 2: Identify missing quotes

   Here, command = echo "Hello" lacks quotes around the entire command string, causing a syntax error.

3. Final Answer:

   Missing quotes around the command string -> Option A

4. Quick Check:

   Command must be a quoted string [OK]

Hint: Always quote command strings in local-exec [OK]

Common Mistakes:

• Forgetting quotes around command
• Using wrong attribute names
• Assuming null_resource disallows provisioners

5. You want to run a local script setup.sh after creating an AWS EC2 instance using Terraform. Which is the best way to use local-exec provisioner to achieve this safely?

hard

A. Run setup.sh manually after Terraform apply

B. Use remote-exec provisioner to run setup.sh on the EC2 instance

C. Use local-exec with command = "./setup.sh" inside the EC2 resource without dependencies

D. Use local-exec with command = "./setup.sh" inside the EC2 resource and add depends_on for the instance

Solution

1. Step 1: Understand local-exec vs remote-exec

   The local-exec provisioner runs commands on your local machine, which is not suitable for running scripts on the EC2 instance itself.

2. Step 2: Use remote-exec for remote commands

   To run a script on the EC2 instance, use the remote-exec provisioner which executes commands on the remote resource.

3. Final Answer:

   Use remote-exec provisioner to run setup.sh on the EC2 instance -> Option B

4. Quick Check:

   remote-exec runs commands on the remote resource [OK]

Hint: Use remote-exec to run scripts on remote instances [OK]

Common Mistakes:

• Using remote-exec for a local script
• Running scripts manually instead of automating
• Adding unnecessary depends_on inside the resource