How to Use Ansible

Ansible is an easy-to-use automation software that can update a server, configure tasks, manage daily server functions and deploys jobs as needed on a schedule of your choosing. It is usually administered from a single location or control server and uses SSH to connect to the remote servers. Because it employs SSH to connect, it is very secure and, there is no software to install on the servers being managed. It can be run from your desktop, laptop or other platforms to assist with automating the tedious tasks which every server owner faces.

Once it is configured, Ansible performs tasks based on an ordered list of assignments in what is called a Playbook. The Playbook outlines what tasks need to be run on the remote server and in what order. Once this is configured, Ansible acts like a bash for-loop command that allows a section of code to be repeated over and over again. The difference between using a bash command and Ansible is that Ansible is idempotent. The term Idempotent sounds a little scary, but it merely means that you can make the same type of request over and over again and unless something has changed, you will get the same result.

Requirements

Source Server Requirements

Ansible requires the installation of Python 2.7 or Python 3.5 on the source server. The source server is where you will be running the tasks in the playbook for the remote servers. The remote servers receive commands defined in the playbook.  A playbook is a file which defines the scripts that will be run on the remote servers.

Let’s start by installing Python on the source server.

root@test:~# apt-get install python

Target Server Requirements

The only requirement from the target server is an open SSH port. Access can also be granted for scp (secure copy) and/or SFTP connections if configured in the /etc/ansible/ansible.cfg file.

Install Ansible On Ubuntu 16.04

To install Ansible on a source Ubuntu server, let’s follow these steps:

root@test:~# apt-get update
 root@test:~# apt-get install software-properties-common
 root@test:~# apt-add-repository ppa:ansible/ansible
 root@test:~# apt-get update
 root@test:~# apt-get install ansible
 (install text)After this operation, 42.0 MB of additional disk space will be used.
 Do you want to continue? [Y/n] y

Answer “Y” to the prompt. The install will complete and take you back to the command prompt. Now, let’s check the version of Ansible installed.

Check Ansible Version

root@test:~# ansible --version
 ansible 2.7.0
   config file = /etc/ansible/ansible.cfg
   configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
   ansible python module location = /usr/lib/python2.7/dist-packages/ansible
   executable location = /usr/bin/ansible
   python version = 2.7.12 (default, Dec  4 2017, 14:50:18) [GCC 5.4.0 20160609]

As an alternative, you can also install Ansible on your CentOS 7 server.

Ansible also can be installed on RedHat, Debian, MacOS, and any of the BSD flavors!

Install Ansible on CentOS 7

In order to install Ansible on a source CentOS 7 server, follow these steps.
First, we need to make sure that the CentOS 7 EPEL repository is added:

[root@test ~]# cat /etc/redhat-release
 CentOS Linux release 7.5.1804 (Core)

[root@test ~]# yum install epel-release
 Loaded plugins: fastestmirror, priorities, universal-hooks
 Loading mirror speeds from cached hostfile
 …
 ...
 Resolving Dependencies
 --> Running transaction check
 ---> Package epel-release.noarch 0:7-11 will be installed
 --> Finished Dependency Resolution
 Dependencies Resolved
 =========================================================================
 Package              Arch          Version       Repository        Size
 =========================================================================
 Installing:
 epel-release         noarch         7-11         system-extras     15 k
 Transaction Summary
 =========================================================================
 Install  1 Package
 Total download size: 15 k
 Installed size: 24 k
 Is this ok [y/d/N]: y
 Downloading packages:
 epel-release-7-11.noarch.rpm                         |  15 kB  00:00:00
 Running transaction check
 Running transaction test
 Transaction test succeeded
 Running transaction
 Installing : epel-release-7-11.noarch                             1/1
 Verifying  : epel-release-7-11.noarch                             1/1
 Installed:
 epel-release.noarch 0:7-11
 Complete!

Select “y”. The EPEL repo will then be added. Once the repository is enabled, we can install Ansible with yum:

root@test:~# yum install ansible
 Loaded plugins: fastestmirror, priorities, universal-hooks
 Loading mirror speeds from cached hostfile
 epel/x86_64/metalink                                  | 18 kB 00:00:00
 * EA4: 208.100.0.204
 * cpanel-addons-production-feed: 208.100.0.204
 * epel: mirrors.liquidweb.com
 epel                                                  | 3.2 kB 00:00:00
 (1/3): epel/x86_64/group_gz                           | 88 kB 00:00:00
 (2/3): epel/x86_64/updateinfo
 (3/3): epel/x86_64/primary                            | 3.6 MB 00:00:00
 epel                                                  12756/12756
 Resolving Dependencies
 … (dependencies check)
 Dependencies Resolved
 ========================================================================
 Package                     Arch Version            Repository Size
 ========================================================================
 Installing:
 ansible                     noarch 2.4.2.0-2.el7    system-extras 7.6 M
 Installing for dependencies:
 21 k
 Transaction Summary
 ========================================================================
 Install  1 Package (+17 Dependent packages)
 Total download size: 12 M
 Installed size: 58 M
 Is this ok [y/d/N]:

Select “y” to start the Ansible install:

Is this ok [y/d/N]: y
 … Downloading 18 packages:
 ---------------------------------------------------------------
 Total                                  30 MB/s | 12 MB 00:00:00
 Running transaction check
 Running transaction test
 Transaction test succeeded
 Running transaction
 … (installing 18 python related software)
 ...
 Installed:
 ansible.noarch 0:2.4.2.0-2.el7
 Dependency Installed:
 ... (dependencies verified)
 Complete!

Check Ansible Version on CentOS 7

Now, let’s verify the version installed:

root@test ~]# ansible --version
 ansible 2.4.2.0
 config file = /etc/ansible/ansible.cfg
 configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
 ansible python module location = /usr/lib/python2.7/site-packages/ansible
 executable location = /usr/bin/ansible
 python version = 2.7.5 (default, Jul 13 2018, 13:06:57) [GCC 4.8.5 20150623 (Red Hat 4.8.5-28)]

Setting Up Ansible Connections

Initially, we will be adding server names or IP’s to the /etc/ansible/hosts file to identify which “ungrouped” servers and “groups” of servers we are going to be connecting to. We mention ungrouped and grouped in this specific order because this is the way the Ansible hosts file is usually arranged.

We can use any name we like for the hosts file itself but typically it is just called hosts. Ansible also states that the hosts file can also be identified as an inventory file and, you can have multiple inventory files.

Let's start by opening the hosts file with vim and inserting some entries into the file.

root@test:~# vim /etc/ansible/hosts

Here is what the default hosts file will look like:

# This is the default ansible 'hosts' file.
 #
 # It should live in /etc/ansible/hosts
 #
 #   - Comments begin with the '#' character
 #   - Blank lines are ignored
 #   - Groups of hosts are delimited by [header] elements
 #   - You can enter hostnames or ip addresses
 #   - A hostname/ip can be a member of multiple groups
 # Example 1: Ungrouped hosts, specify before any group headers.
 #green.example.com
 #blue.example.com
 #192.168.100.1
 #192.168.100.10
 # Example 2: A collection of hosts belonging to the 'webservers' group
 #[webservers]
 #alpha.example.org
 #beta.example.org
 #192.168.1.100
 #192.168.1.110
 # If you have multiple hosts following a pattern you can specify
 # them like this:
 #www[001:006].example.com
 # Example 3: A collection of database servers in the 'dbservers' group
 #[dbservers]
 #
 #db01.intranet.mydomain.net
 #db02.intranet.mydomain.net
 #10.25.1.56
 #10.25.1.57
 # Here's another example of host ranges, this time there are no
 # leading 0s:
 #db-[99:101]-node.example.com

As you can see, there are individual servers “#green.example.com”, and groups like #[webservers] which have multiple servers under the group and, another section with multiple servers listed like #db-[99:101]-node.example.com which identifies all of the individual servers from 99-101; eg.

• db-99-node.example.com
• db-100-node.example.com
• db-101-node.example.com

So, let's quickly add another server to the #[webservers] group:

#[webserver1]
 #alpha.example.org
 #beta.example.org
 #192.168.1.100
 #192.168.1.110gamma.example.com

Now, simply save the file using :wq.

SSH Keys

You can set up public SSH keys from the control server to log in to those remote servers noted in the hosts file. In this case, you simply want to make sure your local SSH keys are located in the /root/.ssh/authorized_keys file on the remote systems. (Depending on your setup, you may wish to use Ansible’s --private-key option to specify a .pem file instead)

Verify Ansible Connections

The ansible inventory file (/etc/ansible/hosts) contains the server names you will have control over and can run tasks against. To verify Ansible’s connectivity, run:

ansible remote -m ping

Ansible Playbooks

Ansible playbooks (also called inventory files) define the tasks ran on the remote servers. You can have one playbook or multiple playbooks to accomplish different tasks on different servers.  To easily apply a task to all of the servers in a pool, use the ‘group’ name to apply the task for that group (using the example above, you would use the [webserver1] in the command.

Create a Playbook

Step 1: In order to create a playbook, let’s create a new file in the /etc/ansible/playbooks/ folder:

mkdir -p /etc/ansible/playbooks/ && touch /etc/ansible/playbooks/playbook.yml && vim /etc/ansible/playbooks/playbook.yml

Step 2: Let's add a server and file entry into the playbook filer:

(Click the insert key to open VIM’s edit access on the file)

- hosts: gamma.example.com
   tasks:
       - name: Create file
         file:
             path: /tmp/test.txt
             state: touch

Once we have added the entry, let’s save the file using :wq.

Step 3: Now, to set up 0644 permissions on that file, we can reopen it and add another line defining the permission set.

- hosts: gamma.example.com
 tasks:
     - name: Create file
       file:
           path: /tmp/test.txt
           state: touch            mode: "u=rw,g=r,o=r"

Again, let’s save the file using:wq.

Step 4: Next, let’s create a folder and then place a text file in it using Ansible. We will add another section defining the element needed.

- hosts: gamma.example.com
   Tasks:       - name: Create folder
         path: /home/tmp/
             state: directory
             mode: 0755
       - name: Create file
         file:
             path: /home/tmp/test.txt
             state: touch            mode: "u=rw,g=r,o=r"

Once we have added this entry, save the file using:wq.

Running a Playbook

To start a playbook, simply run:

ansible-playbook /etc/ansible/playbooks/playbook.yml

Or if you have multiple playbooks in a folder, can run a specific playbook using the -i <path> option from the command line:

ansible-playbook -i /etc/ansible/playbooks/playbook1.yml

In addition to .yaml files, Ansible can use .json files as well to control the playbook. It is also very easy to convert bash or shell scripts into playbooks as well!

Schedule a Playbook Using Cron

As an additional option, you can schedule a playbook to run at a specific time using your servers cron command! To accomplish this, log in to your server as root and run the following command:

crontab -e

This command opens a temporary cron file in your system’s default text editor and then simply add a line like so:

0 4 * * * /usr/bin/ansible-playbook /etc/ansible/playbooks/playbook.yml

This will run the/etc/ansible/playbooks/playbook.yml file at 0400 a.m. using the ansible-playbook command.

Troubleshooting A Playbook

Sometimes, a set of commands in the playbook file may fail. If it does, you have several options to address this. Generally, playbooks will simply stop completing the commands in the playbook. If this occurs, you can define a follow-up task in the playbook to overlook the error by adding another section like so:

- name: ignore this error
   command: /bin/false
   ignore_errors: yes

Unreachable Hosts
this command will only work when the task is run but returns a "failed" value.

If Ansible fails to connect to a server, it will set the host as being ‘UNREACHABLE’. This effectively removes the server temporarily from the list of active hosts for that task. To correct this, we can use an entry to reactivate them and have all current hosts previously indicated as being unreachable cleared, so subsequent tasks can use the playbook again.

meta: clear_host_errors

Handlers and Failure

A handler is simply a specially named task that runs when told to by another task. Handlers are executed at the end of the playbook by default as opposed to other tasks, which are executed immediately when defined within the playbook. This behavior can be modified by using the

--force-handlers

command-line option, or by including

force_handlers: True

in a playbook, or adding

force_handlers = True

in the ansible.cfg file.

If you want to force a handler to run in the middle of two separate tasks instead of at the end of the playbook, you will need to add this entry between the two tasks:

- meta: flush_handlers

When handlers are “forced” like this, they will run when notified even if a task fails on that host.

Handlers will only be visible in the output if they have actually been executed. Also, handlers are only fired when there are changes made by a task. For example, a task may update a specific configuration file and then notify a handler to restart a service. If a task in the same playbook fails later on, the service will not be restarted despite the previous configuration change.

Overall, Ansible is an indispensable tool for managing and administrating a single server or an entire group of geographically diverse servers.