How to disable host key checking in Ansible

Introduction

Ansible is a powerful IT automation tool that simplifies infrastructure management and deployment. However, when working with remote hosts, Ansible's default host key checking can sometimes create challenges. This tutorial will guide you through the process of disabling host key checking in Ansible, ensuring a smooth and efficient automation experience.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL ansible(("`Ansible`")) -.-> ansible/InventoryManagementGroup(["`Inventory Management`"]) ansible(("`Ansible`")) -.-> ansible/ModuleOperationsGroup(["`Module Operations`"]) ansible/InventoryManagementGroup -.-> ansible/host_variables("`Set Host Variables`") ansible/ModuleOperationsGroup -.-> ansible/ping("`Network Test`") ansible/ModuleOperationsGroup -.-> ansible/shell("`Execute Shell Commands`") ansible/ModuleOperationsGroup -.-> ansible/file("`Manage Files/Directories`") ansible/ModuleOperationsGroup -.-> ansible/command("`Execute Commands`") subgraph Lab Skills ansible/host_variables -.-> lab-415240{{"`How to disable host key checking in Ansible`"}} ansible/ping -.-> lab-415240{{"`How to disable host key checking in Ansible`"}} ansible/shell -.-> lab-415240{{"`How to disable host key checking in Ansible`"}} ansible/file -.-> lab-415240{{"`How to disable host key checking in Ansible`"}} ansible/command -.-> lab-415240{{"`How to disable host key checking in Ansible`"}} end

Understanding Host Key Checking

Host key checking is a security feature in Ansible that helps to verify the identity of the remote hosts you are connecting to. When you connect to a remote host for the first time, Ansible will store the host's public key in a known_hosts file. On subsequent connections, Ansible will compare the host's public key to the one stored in the known_hosts file to ensure that the remote host is the same one you connected to previously.

This process helps to prevent man-in-the-middle attacks, where an attacker could intercept your connection and impersonate the remote host. By verifying the host's identity, Ansible can ensure that you are communicating with the correct remote host.

However, in some cases, you may want to disable host key checking, for example, when working with ephemeral or dynamically provisioned hosts, or when testing your Ansible playbooks. Disabling host key checking can make the connection process faster and more convenient, but it also increases the risk of a man-in-the-middle attack.

graph LR A[Client] -- Connect --> B[Remote Host] B -- Public Key --> A A -- Verify Public Key --> C[Known Hosts File]

Action	Description
Connect	The client connects to the remote host.
Public Key	The remote host sends its public key to the client.
Verify Public Key	The client compares the received public key to the one stored in the known_hosts file.

Disabling Host Key Checking

To disable host key checking in Ansible, you can use the following methods:

Environment Variable

You can set the ANSIBLE_HOST_KEY_CHECKING environment variable to False to disable host key checking globally:

export ANSIBLE_HOST_KEY_CHECKING=False
ansible-playbook my_playbook.yml

Ansible Configuration File

You can also disable host key checking by setting the host_key_checking option in the Ansible configuration file (/etc/ansible/ansible.cfg or ~/.ansible.cfg):

[defaults]
host_key_checking = False

Ansible Command-line Option

Alternatively, you can disable host key checking for a specific Ansible command by using the --ask-vault-pass or -k option:

ansible-playbook my_playbook.yml --ask-vault-pass -k

This will prompt you to enter the vault password and disable host key checking for the current command.

graph LR A[Ansible] -- Set Environment Variable --> B[ANSIBLE_HOST_KEY_CHECKING=False] A -- Set Configuration File --> C[ansible.cfg] A -- Use Command-line Option --> D[--ask-vault-pass/-k]

By disabling host key checking, you can simplify the connection process and make it easier to work with dynamic or ephemeral hosts. However, it's important to note that this also increases the risk of a man-in-the-middle attack, so it's recommended to only disable host key checking in non-production environments or when you're confident that the remote hosts are trusted.

Configuring Host Key Checking

If you prefer to keep host key checking enabled, you can configure it to suit your needs. Here are a few options:

Manually Accepting Host Keys

When you connect to a remote host for the first time, Ansible will prompt you to accept the host's public key. You can manually accept the key by typing "yes" when prompted:

The authenticity of host 'example.com (192.168.1.100)' can't be established.
ECDSA key fingerprint is SHA256:abcd1234efgh5678.
Are you sure you want to continue connecting (yes/no)? yes

This will add the host's public key to the known_hosts file, and Ansible will use it to verify the host's identity on subsequent connections.

Automatically Accepting Host Keys

Alternatively, you can configure Ansible to automatically accept host keys by setting the host_key_auto_add option in the Ansible configuration file:

[defaults]
host_key_auto_add = True

This will automatically add new host keys to the known_hosts file without prompting you.

Specifying a Custom Known Hosts File

By default, Ansible uses the ~/.ssh/known_hosts file to store host keys. However, you can specify a custom known_hosts file by setting the ANSIBLE_SSH_ARGS environment variable:

export ANSIBLE_SSH_ARGS="-o UserKnownHostsFile=/path/to/custom/known_hosts"
ansible-playbook my_playbook.yml

This can be useful if you want to maintain separate known_hosts files for different environments or projects.

graph LR A[Ansible] -- Prompt for Manual Acceptance --> B[known_hosts file] A -- Automatically Accept --> C[known_hosts file] A -- Specify Custom File --> D[/path/to/custom/known_hosts]

By configuring host key checking, you can strike a balance between security and convenience, ensuring that your Ansible connections are secure while still allowing for efficient workflow.

Summary

By disabling host key checking in Ansible, you can streamline your automation workflows, reduce friction, and improve the overall efficiency of your infrastructure management. This tutorial has provided a comprehensive overview of the process, covering the understanding of host key checking, the steps to disable it, and the configuration options available. With these insights, you can now confidently implement this technique and enhance your Ansible-powered automation capabilities.