How does Ansible connect to managed nodes?
Jun 24, 2025 am 12:20 AMAnsible communicates with managed nodes via SSH without the need for installing agents or additional software. 1. SSH connection is used by default. SSH key authentication is recommended. You can also use the password to add the --ask-pass parameter. 2. SSH behavior can be controlled through inventory files or ansible.cfg, such as specifying a user or private key. 3. Support multiplexed SSH connections to improve performance. 4. Inventory, host IP, user, key and other information can be defined. 5. In addition to SSH, it also supports Local, Docker, WinRM and other connection methods, which can be specified through the ansible_connection variable. 6. It is necessary to ensure that DNS resolution, firewall opens 22 ports and correctly sets SSH directory permissions. 7. When using sudo, you need to set it to become:yes or add the -b parameter in the playbook.
Ansible connects to managed nodes using SSH by default, which is both secure and widely supported. It doesn't require any agents or additional software installed on the target machines, making it lightweight and easy to scale.
SSH-based Communication
The primary method Ansible uses to connect to managed nodes is SSH. This means that Ansible needs network-level access to the node and valid credentials (like a username and password or SSH key) to authenticate.
- SSH keys are the most common and recommended way to authenticate.
- If you're not using SSH keys, you can also use passwords, but this requires running Ansible with the
--ask-pass
flag. - You can control how SSH connections behave using settings in your inventory file or
ansible.cfg
, such as settingansible_ssh_user
or specifying a custom SSH key withansible_ssh_private_key_file
.
One thing to note is that Ansible will try to reuse SSH connections by default via ControlPersist, which improves performance when running multiple tasks against the same host.
Inventory Setup Matters
How you define your hosts in the inventory directly affects how Ansible connects to them.
-
A basic inventory entry might look like:
webserver01 ansible_host=192.168.1.10
Here,
ansible_host
tells Ansible which IP to connect to. You can also specify connection details inline:
webserver01 ansible_host=192.168.1.10 ansible_user=myuser ansible_ssh_private_key_file=~/.ssh/id_rsa_web
This flexibility lets you manage different systems with different login requirements from one central point without changing playbooks.
Connection Alternatives
While SSH is the default and most commonly used transport, Ansible supports other connection types for special cases:
- Local : Run tasks directly on the control machine.
- Docker : Connects to containers directly using the Docker CLI.
- WinRM : Used for connecting to Windows hosts.
- Paramiko or OpenSSH : These are two Python-based implementations Ansible can fall back on if needed.
You can choose a different connection type per host or group using the ansible_connection
variable. For example, to connect to a Windows host:
winhost01 ansible_connection=winrm ansible_user=Administrator ansible_password=secret
Small Details That Make a Different
A few small but important points often get overlooked:
- DNS resolution must work from the control node to the managed nodes — either through proper DNS setup or
/etc/hosts
. - Firewalls and port access (typically TCP 22 for SSH) must allow connectivity.
- When using SSH keys, permissions on
.ssh
directories and private keys matter — overly permitted settings may cause SSH to reject the connection.
Also, if you're using sudo on the managed node, you'll want to set become: yes
in your playbook or use the -b
flag when running ad-hoc commands. Ansible handles privilege escalation separately from the initial connection, so even if SSH is fine, missing sudo rights can still break things.
Basically that's it.
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