Chapter 2. Preparing a control node and managed nodes to use RHEL System Roles

Procedure

1. Install the rhel-system-roles package:

   [root@control-node]# yum install rhel-system-roles

   This command installs the ansible-core package as a dependency.

2. Create a user named ansible to manage and run playbooks:

   [root@control-node]# useradd ansible

3. Switch to the newly created ansible user:

   [root@control-node]# su - ansible

   Perform the rest of the procedure as this user.

4. Create an SSH public and private key:

   [ansible@control-node]$ ssh-keygen
   Generating public/private rsa key pair.
   Enter file in which to save the key (/home/ansible/.ssh/id_rsa): <password>
   ...

   Use the suggested default location for the key file.

5. Optional: To prevent Ansible from prompting you for the SSH key password each time you establish a connection, configure an SSH agent.

6. Create the ~/.ansible.cfg file with the following content:

   [defaults]
   inventory = /home/ansible/inventory
   remote_user = ansible
   
   [privilege_escalation]
   become = True
   become_method = sudo
   become_user = root
   become_ask_pass = True

   Note

   Settings in the ~/.ansible.cfg file have a higher priority and override settings from the global /etc/ansible/ansible.cfg file.

   With these settings, Ansible performs the following actions:

   • Manages hosts in the specified inventory file.
   • Uses the account set in the remote_user parameter when it establishes SSH connections to managed nodes.
   • Uses the sudo utility to execute tasks on managed nodes as the root user.
   • Prompts for the root password of the remote user every time you apply a playbook. This is recommended for security reasons.

7. Create an ~/inventory file in INI or YAML format that lists the hostnames of managed hosts. You can also define groups of hosts in the inventory file. For example, the following is an inventory file in the INI format with three hosts and one host group named US:

   managed-node-01.example.com
   
   [US]
   managed-node-02.example.com ansible_host=192.0.2.100
   managed-node-03.example.com

   Note that the control node must be able to resolve the hostnames. If the DNS server cannot resolve certain hostnames, add the ansible_host parameter next to the host entry to specify its IP address.

Procedure

1. Create a user named ansible:

   [root@managed-node-01]# useradd ansible

   The control node later uses this user to establish an SSH connection to this host.

2. Set a password for the ansible user:

   [root@managed-node-01]# passwd ansible
   Changing password for user ansible.
   New password: <password>
   Retype new password: <password>
   passwd: all authentication tokens updated successfully.

   You must enter this password when Ansible uses sudo to perform tasks as the root user.

3. Install the ansible user’s SSH public key on the managed node:

   1. Log in to the control node as the ansible user, and copy the SSH public key to the managed node:

      [ansible@control-node]$ ssh-copy-id managed-node-01.example.com
      /usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/ansible/.ssh/id_rsa.pub"
      The authenticity of host 'managed-node-01.example.com (192.0.2.100)' can't be established.
      ECDSA key fingerprint is SHA256:9bZ33GJNODK3zbNhybokN/6Mq7hu3vpBXDrCxe7NAvo.

   2. When prompted, connect by entering yes:

      Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
      /usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
      /usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys

   3. When prompted, enter the password:

      ansible@managed-node-01.example.com's password: <password>
      
      Number of key(s) added: 1
      
      Now try logging into the machine, with:   "ssh '<managed-node-01.example.com>'"
      and check to make sure that only the key(s) you wanted were added.

   4. Verify the SSH connection by remotely executing a command on the control node:

      [ansible@control-node]$ ssh <managed-node-01.example.com> whoami
      ansible

4. Create a sudo configuration for the ansible user:

   1. Create and edit the /etc/sudoers.d/ansible file by using the visudo command:

      [root@managed-node-01]# visudo /etc/sudoers.d/ansible

      The benefit of using visudo over a normal editor is that this utility provides basic sanity checks and checks for parse errors before installing the file.

   2. Configure a sudoers policy in the /etc/sudoers.d/ansible file that meets your requirements, for example:

      • To grant permissions to the ansible user to run all commands as any user and group on this host after entering the ansible user’s password, use:

        ansible ALL=(ALL) ALL

      • To grant permissions to the ansible user to run all commands as any user and group on this host without entering the ansible user’s password, use:

        ansible ALL=(ALL) NOPASSWD: ALL

   Alternatively, configure a more fine-granular policy that matches your security requirements. For further details on sudoers policies, see the sudoers(5) man page.

Verification

1. Verify that you can execute commands from the control node on an all managed nodes:

   [ansible@control-node]$ ansible all -m ping
   BECOME password: <password>
   managed-node-01.example.com | SUCCESS => {
       	"ansible_facts": {
       	    "discovered_interpreter_python": "/usr/bin/python3"
       	},
       	"changed": false,
       	"ping": "pong"
   }
   ...

   The hard-coded all group dynamically contains all hosts listed in the inventory file.

2. Verify that privilege escalation works correctly by running the whoami utility on a managed host by using the Ansible command module:

   [ansible@control-node]$ ansible managed-node-01.example.com -m command -a whoami
   BECOME password: <password>
   managed-node-01.example.com | CHANGED | rc=0 >>
   root

   If the command returns root, you configured sudo on the managed nodes correctly.