Connection blocks for SSH in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a connection block in Terraform when using SSH?

A connection block tells Terraform how to connect to a remote machine using SSH. It provides details like the host address, user name, and authentication method so Terraform can run commands or copy files on that machine.

beginner

Which key fields are commonly used inside a Terraform SSH connection block?

Common fields include host (IP or hostname), user (username to log in), private_key (SSH private key content), and port (SSH port, usually 22).

intermediate

How do you specify the SSH private key in a Terraform connection block?

You use the private_key field and provide the private key as a string. For example, you can read it from a file using Terraform's file() function.

beginner

True or False: The connection block is required for Terraform to manage resources on remote machines via SSH.

True. Without a connection block, Terraform does not know how to connect to the remote machine to execute commands or transfer files.

beginner

What happens if you omit the port field in a Terraform SSH connection block?

Terraform will use the default SSH port 22 to connect to the remote machine.

Which field in a Terraform connection block specifies the username for SSH?

A user

B host

C private_key

D port

The user field specifies the username Terraform uses to log in via SSH.

What is the default SSH port used if the port field is not set in the connection block?

A 443

B 21

C 80

D 22

SSH uses port 22 by default.

How can you provide the SSH private key content in a Terraform connection block?

A Using the <code>password</code> field

B Using the <code>private_key</code> field with the key as a string

C Using the <code>host</code> field

D Using the <code>user</code> field

The private_key field holds the SSH private key content as a string.

Which Terraform resource block commonly uses a connection block for SSH?

A aws_instance

B azurerm_virtual_network

C null_resource

D google_storage_bucket

The null_resource often uses connection blocks to run remote commands via SSH.

What is the main reason to use a connection block in Terraform?

A To connect to a remote machine for executing commands

B To define the cloud provider

C To specify resource dependencies

D To set environment variables

Connection blocks tell Terraform how to connect to remote machines to run commands or copy files.

Explain how a Terraform connection block is used to connect to a remote machine via SSH.

Think about what information Terraform needs to log in and run commands remotely.

Describe what happens if you omit the port field in a Terraform SSH connection block.

Consider the standard SSH port and how Terraform behaves without explicit port info.

Practice

1. What is the main purpose of a connection block in Terraform when using SSH?

easy

A. To specify the Terraform backend storage

B. To define how Terraform connects to remote machines for running commands or copying files

C. To configure the cloud provider credentials

D. To create a new SSH key pair automatically

Solution

1. Step 1: Understand the role of connection blocks

   Connection blocks specify how Terraform connects to remote machines, typically using SSH, to run commands or transfer files during provisioning.

2. Step 2: Differentiate from other configurations

   SSH key creation, cloud credentials, and backend storage are configured elsewhere, not in connection blocks.

3. Final Answer:

   To define how Terraform connects to remote machines for running commands or copying files -> Option B

4. Quick Check:

   Connection block purpose = Define SSH connection [OK]

Hint: Connection blocks set SSH details for remote commands [OK]

Common Mistakes:

• Confusing connection block with SSH key creation
• Mixing connection block with cloud provider config
• Thinking connection block manages backend storage

2. Which of the following is the correct syntax to specify an SSH connection block in Terraform?

easy

A. connection { type = "winrm" user = "ubuntu" host = self.public_ip private_key = file("~/.ssh/id_rsa") }

B. connection { protocol = "ssh" username = "ubuntu" address = self.public_ip key = file("~/.ssh/id_rsa") }

C. connection { ssh_user = "ubuntu" ssh_host = self.public_ip ssh_key = file("~/.ssh/id_rsa") }

D. connection { user = "ubuntu" host = self.public_ip private_key = file("~/.ssh/id_rsa") }

Solution

1. Step 1: Recall Terraform connection block syntax

   The correct keys are user, host, and private_key. The type key is not required for SSH as it is the default.

2. Step 2: Identify the valid syntax

   connection { user = "ubuntu" host = self.public_ip private_key = file("~/.ssh/id_rsa") } uses correct keys without unnecessary or incorrect ones like type or protocol.

3. Final Answer:

   connection { user = "ubuntu" host = self.public_ip private_key = file("~/.ssh/id_rsa") } -> Option D

4. Quick Check:

   Correct keys = user, host, private_key [OK]

Hint: Use user, host, private_key keys in connection block [OK]

Common Mistakes:

• Adding unnecessary 'type' or 'protocol' keys
• Using wrong key names like ssh_user or username
• Omitting required keys like user or host

3. Given this Terraform snippet, what will happen when Terraform tries to connect?

connection {
  user = "admin"
  host = aws_instance.example.public_ip
  private_key = file("~/.ssh/id_rsa")
  timeout = "2m"
}

medium

A. Terraform will connect but ignore the timeout setting

B. Terraform will fail because timeout must be a number, not a string

C. Terraform will connect using SSH as user 'admin' with a 2-minute timeout

D. Terraform will connect using default user instead of 'admin'

Solution

1. Step 1: Analyze connection block fields

   The block correctly sets user, host, private_key, and timeout. Timeout accepts a duration string like "2m".

2. Step 2: Understand Terraform SSH connection behavior

   Terraform uses these values to connect via SSH as user 'admin' with a 2-minute timeout for connection attempts.

3. Final Answer:

   Terraform will connect using SSH as user 'admin' with a 2-minute timeout -> Option C

4. Quick Check:

   Timeout string '2m' is valid duration [OK]

Hint: Timeout accepts duration strings like '2m' for SSH connections [OK]

Common Mistakes:

• Thinking timeout must be numeric only
• Assuming default user is used ignoring 'user' key
• Believing timeout is ignored by Terraform

4. Identify the error in this Terraform connection block:

connection {
  user = "ec2-user"
  host = aws_instance.web.public_ip
  private_key = "~/.ssh/id_rsa"
}

medium

A. private_key should use file() function to read the key content

B. host should be a static IP, not a resource attribute

C. user must be 'ubuntu' for AWS instances

D. Missing 'type = "ssh"' in connection block

Solution

1. Step 1: Check private_key value type

   The private_key must contain the actual key content, not just the file path string. Using file("~/.ssh/id_rsa") reads the key content.

2. Step 2: Validate other fields

   Host can be a resource attribute, user can be 'ec2-user' for Amazon Linux, and 'type' defaults to SSH so it's optional.

3. Final Answer:

   private_key should use file() function to read the key content -> Option A

4. Quick Check:

   private_key needs file() to read key [OK]

Hint: Use file() to load private_key content, not just path string [OK]

Common Mistakes:

• Assigning private_key a file path string directly
• Assuming host cannot be a resource attribute
• Forcing user to 'ubuntu' regardless of OS

5. You want to run a remote command on an AWS instance using Terraform. Which connection block setup is best practice to ensure a reliable SSH connection?

hard

A. connection {
user = "ec2-user"
host = aws_instance.app.public_ip
private_key = file("~/.ssh/id_rsa")
timeout = "5m"
agent = true
}

B. connection {
user = "ec2-user"
host = aws_instance.app.public_ip
private_key = file("~/.ssh/id_rsa")
timeout = "1m"
agent = false
}

C. connection {
user = "ec2-user"
host = aws_instance.app.private_ip
private_key = file("~/.ssh/id_rsa")
timeout = "5m"
agent = true
}

D. connection {
user = "ubuntu"
host = aws_instance.app.public_ip
private_key = file("~/.ssh/id_rsa")
timeout = "30s"
agent = false
}

Solution

1. Step 1: Choose correct user and host

   For AWS Amazon Linux, user is usually 'ec2-user'. Public IP is needed for SSH from outside the VPC.

2. Step 2: Set appropriate timeout and agent

   A longer timeout like "5m" helps with slow connections. Using SSH agent forwarding (agent = true) can improve key management.

3. Step 3: Compare options

   connection { user = "ec2-user" host = aws_instance.app.public_ip private_key = file("~/.ssh/id_rsa") timeout = "5m" agent = true } uses correct user, public IP, sufficient timeout, and enables agent forwarding, matching best practices.

4. Final Answer:

   connection { user = "ec2-user" host = aws_instance.app.public_ip private_key = file("~/.ssh/id_rsa") timeout = "5m" agent = true } -> Option A

5. Quick Check:

   Public IP, correct user, timeout 5m, agent true = best practice [OK]

Hint: Use public IP, correct user, 5m timeout, and agent true for reliability [OK]

Common Mistakes:

• Using private IP when public IP is needed
• Setting too short timeout causing failures
• Disabling agent forwarding unnecessarily
• Using wrong user for the OS