Automating Initial Server Setup with Ansible on Ubuntu 18.04

Introduction

When you first create a new Ubuntu 18.04 server, there are a few configuration steps that you should take early on as part of the basic setup. This will increase the security and usability of your server, working as a solid foundation for subsequent actions.

While you can complete these steps manually, automating the process will save you time and eliminate human error. With the popularization of containerized applications and microservices, server automation now plays an essential role in systems administration. It is also a way to establish standard procedures for new servers.

This guide explains how to use Ansible to automate the steps contained in our Initial Server Setup Guide. Ansible is a modern configuration management tool that can be used to automate the provisioning and configuration of remote systems.

Pre-Flight Check

In order to execute the automated setup provided by the playbook we’re discussing in this guide, you’ll need:

  • Ansible installed either on your local machine or on a remote server that you have set up as an Ansible Control Node. You can follow Step 1 of the tutorial How to Install and Configure Ansible on Ubuntu 18.04 to get this set up.
  • Root access to one or more Ubuntu 18.04 servers that will be managed by Ansible.

Before running a playbook, it’s important to make sure Ansible is able to connect to your servers via SSH and run Ansible modules using Python. The next two sections cover how to set up your Ansible inventory to include your servers and how to run ad-hoc Ansible commands to test for connectivity and valid credentials.

Inventory File

The inventory file contains information about the hosts you’ll manage with Ansible. You can include anywhere from one to several hundred of servers in your inventory file, and hosts can be organized into groups and subgroups. The inventory file is also often used to set variables that will be valid for certain hosts and groups only, in order to be used within playbooks and templates. Some variables can also affect the way a playbook is run, like the ansible_python_interpreter variable that we’ll see in a moment.

To inspect the contents of your default Ansible inventory, open the /etc/ansible/hosts file using your command-line editor of choice, on your local machine or an Ansible Control Node:


  • sudo nano /etc/ansible/hosts

Note: some Ansible installations won’t create a default inventory file. If the file doesn’t exist in your system, you can create a new file at /etc/ansible/hosts or provide a custom inventory path using the -i parameter when running commands and playbooks.

The default inventory file provided by the Ansible installation contains a number of examples that you can use as references for setting up your inventory. The following example defines a group named servers with three different servers in it, each identified by a custom alias: server1, server2, and server3:

/etc/ansible/hosts
[servers]
server1 ansible_host=203.0.113.111
server2 ansible_host=203.0.113.112
server3 ansible_host=203.0.113.113

[servers:vars]
ansible_python_interpreter=/usr/bin/python3

The server:vars subgroup sets the ansible_python_interpreter host parameter that will be valid for all hosts included in the servers group. This parameter makes sure the remote server uses the /usr/bin/python3 Python 3 executable instead of /usr/bin/python (Python 2.7), which is not present on recent Ubuntu versions.

To finish setting up your inventory file, replace the highlighted IPs with the IP addresses of your servers. When you’re finished, save and close the file by pressing CTRL+X then y to confirm changes and then ENTER.

Now that your inventory file is ready, it’s time to test connectivity to your nodes

Testing Connectivity

After setting up the inventory file to include your servers, it’s time to check if Ansible is able to connect to these servers and run commands via SSH. For this guide, we will be using the Ubuntu root account because that’s typically the only account available by default on newly created servers. This playbook will create a new non-root user with sudo privileges that you should use in subsequent interactions with the remote server.

From your local machine or Ansible Control Node, run:


  • ansible -m ping all -u root

This command will use the built-in ping Ansible module to run a connectivity test on all nodes from your default inventory, connecting as root. The ping module will test:
if hosts are accessible;
if you have valid SSH credentials;
if hosts are able to run Ansible modules using Python.

If instead of key-based authentication you’re using password-based authentication to connect to remote servers, you should provide the additional parameter -k to the Ansible command, so that it will prompt you for the password of the connecting user.


  • ansible -m ping all -u root -k

Note: Keep in mind that some servers might have additional security measures against password-based authentication as the root user, and in some cases you might be required to manually log in to the server to change the initial root password.

You should get output similar to this:


Output
server1 | SUCCESS => { "changed": false, "ping": "pong" } server2 | SUCCESS => { "changed": false, "ping": "pong" } server3 | SUCCESS => { "changed": false, "ping": "pong" }

If this is the first time you’re connecting to these servers via SSH, you’ll be asked to confirm the authenticity of the hosts you’re connecting to via Ansible. When prompted, type yes and then hit Enter to confirm.

Once you get a “pong” reply back from a host, it means you’re ready to run Ansible commands and playbooks on that server.

What Does this Playbook Do?

This Ansible playbook provides an alternative to manually running through the procedure outlined in the Ubuntu 18.04 initial server setup guide and the guide on setting up SSH keys on Ubuntu 18.04.

Running this playbook will cause the following actions to be performed:

  1. The administrative group wheels is created and then configured for passwordless sudo.
  2. A new administrative user is created within that group, using the name specified by the create_user variable.
  3. A public SSH key is copied from the location defined by the variable copy_local_key, and added to the authorized_keys file for the user created in the previous step.
  4. Password-based authentication is disabled for the root user.
  5. The local apt package index is updated and basic packages defined by the variable sys_packages are installed.
  6. The UFW firewall is configured to allow only SSH connections and deny any other requests.

For more information about each of the steps included in this playbook, please refer to our Ubuntu 18.04 initial server setup guide.

Once the playbook has finished running, you’ll be able to log in to the server using the newly created sudo account.

How to Use this Playbook

To get started, we’ll download the contents of the playbook to your Ansible Control Node. This can be either your local machine, or a remote server where you have Ansible installed and your inventory set up.

For your convenience, the contents of the playbook are also included in a further section of this guide.

To download this playbook from the command-line, you can use curl:


  • curl -L https://raw.githubusercontent.com/do-community/ansible-playbooks/master/initial_server_setup/ubuntu1804.yml -o initial_server_setup.yml

This will download the contents of the playbook to a file named initial_server_setup.yml on your current local path. You can examine the contents of the playbook by opening the file with your command-line editor of choice:


  • sudo nano initial_server_setup.yml

Once you’ve opened the playbook file, you should notice a section named vars with three distinct variables that require your attention:

  • create_user: The name of the non-root user account to create and grant sudo privileges to. Our example uses sammy, but you can use whichever username you’d like.
  • copy_local_key: Local path to a valid SSH public key to set up as an authorized key for the new non-root sudo account. The default value points to the current local user’s public key located at ~/.ssh/id_rsa.pub.
  • sys_packages: A list of basic system packages that will be installed using the package manager tool apt.

Once you’re done updating the variables inside initial_server_setup.yml, save and close the file.

You’re now ready to run this playbook on one or more servers. Most playbooks are configured to be executed on all servers from your inventory, by default. We can use the -l flag to make sure that only a subset of servers, or a single server, is affected by the playbook. To execute the playbook only on server1, you can use the following command:


  • ansible-playbook initial_server_setup.yml -l server1

You will get output similar to this:


Output
PLAY [all] *************************************************************************************************************************************** TASK [Make sure we have a 'wheel' group] ********************************************************************************************************* changed: [server1] TASK [Allow 'wheel' group to have passwordless sudo] ********************************************************************************************* changed: [server1] TASK [Create a new regular user with sudo privileges] ******************************************************************************************** changed: [server1] TASK [Set authorized key for remote user] ******************************************************************************************************** changed: [server1] TASK [Disable password authentication for root] ************************************************************************************************** changed: [server1] TASK [Update apt] ******************************************************************************************************************************** changed: [server1] TASK [Install required system packages] ********************************************************************************************************** ok: [server1] TASK [UFW - Allow SSH connections] *************************************************************************************************************** changed: [server1] TASK [UFW - Deny all other incoming traffic by default] ****************************************************************************************** changed: [server1] PLAY RECAP *************************************************************************************************************************************** server1 : ok=9 changed=8 unreachable=0 failed=0

Once the playbook execution is finished, you’ll be able to log in to the server with:


  • ssh sammy@server_domain_or_IP

Remember to replace sammy with the user defined by the create_user variable, and server_domain_or_IP with your server’s hostname or IP address.

In case you have set a custom public key with the copy_local_key variable, you’ll need to provide an extra parameter specifying the location of its private key counterpart:


  • ssh sammy@server_domain_or_IP -i ~/.ssh/ansible_controller_key

After logging in to the server, you can check the UFW firewall’s active rules to confirm that it’s properly configured:


  • sudo ufw status

You should get output similar to this:


Output
Status: active To Action From -- ------ ---- OpenSSH ALLOW Anywhere OpenSSH (v6) ALLOW Anywhere (v6)

This means that the UFW firewall has successfully been enabled. Since this was the last task in the playbook, it confirms that the playbook was fully executed on this server.

The Playbook Contents

You can find the initial server setup playbook in the ansible-playbooks repository in the DigitalOcean Community GitHub organization. To copy or download the script contents directly, click the Raw button towards the top of the script, or click here to view the raw contents directly.

The full contents are also included here for convenience:

initial_server_setup.yml
---
- hosts: all
  remote_user: root
  gather_facts: false
  vars:
    create_user: sammy
    copy_local_key: "{{ lookup('file', lookup('env','HOME') + '/.ssh/id_rsa.pub') }}"
    sys_packages: [ 'curl', 'vim', 'git', 'ufw' ]

  tasks:
    - name: Make sure we have a 'wheel' group
      group:
        name: wheel
        state: present

    - name: Allow 'wheel' group to have passwordless sudo
      lineinfile:
        path: /etc/sudoers
        state: present
        regexp: '^%wheel'
        line: '%wheel ALL=(ALL) NOPASSWD: ALL'
        validate: '/usr/sbin/visudo -cf %s'

    - name: Create a new regular user with sudo privileges
      user:
        name: "{{ create_user }}"
        groups: wheel
        shell: /bin/bash

    - name: Set authorized key for remote user
      authorized_key:
        user: "{{ create_user }}"
        state: present
        key: "{{ copy_local_key }}"

    - name: Disable password authentication for root
      lineinfile:
        path: /etc/ssh/sshd_config
        state: present
        regexp: '^PermitRootLogin'
        line: 'PermitRootLogin prohibit-password'

    - name: Update apt
      apt: update_cache=yes

    - name: Install required system packages
      apt: name={{ sys_packages }} state=latest

    - name: UFW - Allow SSH connections
      ufw:
        rule: allow
        name: OpenSSH

    - name: UFW - Deny all other incoming traffic by default
      ufw:
        state: enabled
        policy: deny
        direction: incoming

Feel free to modify this playbook or include new tasks to best suit your individual needs within your own workflow.

Conclusion

Automating the initial server setup can save you time, while also making sure your servers will follow a standard configuration that can be improved and customized to your needs. With the distributed nature of modern applications and the need for more consistency between different staging environments, automation like this becomes a necessity.

In this guide, we demonstrated how to use Ansible for automating the initial tasks that should be executed on a fresh server, such as creating a non-root user with sudo access, enabling UFW and disabling remote root login.

If you’d like to include new tasks in this playbook to further customize your initial server setup, please refer to our introductory Ansible guide Configuration Management 101: Writing Ansible Playbooks.

Originally posted on DigitalOcean Community Tutorials
Author: DigitalOcean

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