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Chapter 2. Preparing a control node and managed nodes to use RHEL system roles

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Before you can use individual RHEL system roles to manage services and settings, you must prepare the control node and managed nodes.

2.1. Preparing a control node on RHEL 8

Before using RHEL system roles, you must configure a control node. This system then configures the managed hosts from the inventory according to the playbooks.

Prerequisites

Procedure

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

    [root@control-node]# useradd ansible
  2. Switch to the newly created ansible user:

    [root@control-node]# su - ansible

    Perform the rest of the procedure as this user.

  3. 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):
    Enter passphrase (empty for no passphrase): <password>
    Enter same passphrase again: <password>
    ...

    Use the suggested default location for the key file.

  4. Optional: To prevent Ansible from prompting you for the SSH key password each time you establish a connection, configure an SSH agent.
  5. 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.
  6. 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.

  7. Install RHEL system roles:

    • On a RHEL host without Ansible Automation Platform, install the rhel-system-roles package:

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

      This command installs the collections in the /usr/share/ansible/collections/ansible_collections/redhat/rhel_system_roles/ directory, and the ansible-core package as a dependency.

    • On Ansible Automation Platform, perform the following steps as the ansible user:

      1. Define Red Hat automation hub as the primary source for content in the ~/.ansible.cfg file.
      2. Install the redhat.rhel_system_roles collection from Red Hat automation hub:

        [ansible@control-node]$ ansible-galaxy collection install redhat.rhel_system_roles

        This command installs the collection in the ~/.ansible/collections/ansible_collections/redhat/rhel_system_roles/ directory.

Next step

2.2. Preparing a managed node

Managed nodes are the systems listed in the inventory and which will be configured by the control node according to the playbook. You do not have to install Ansible on managed hosts.

Prerequisites

  • You prepared the control node. For more information, see Preparing a control node on RHEL 8.
  • You have SSH access from the control node.

    Important

    Direct SSH access as the root user is a security risk. To reduce this risk, you will create a local user on this node and configure a sudo policy when preparing a managed node. Ansible on the control node can then use the local user account to log in to the managed node and run playbooks as different users, such as root.

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 checks, such as 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) manual 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 all managed nodes by using the Ansible command module:

    [ansible@control-node]$ ansible all -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.

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