How to use Ansible to patch systems and install applications

Have you ever wondered how to patch your systems, reboot, and continue working?

If so, you'll be interested in Ansible, a simple configuration management tool that can make some of the hardest work easy. For example, system administration tasks that can be complicated, take hours to complete, or have complex requirements for security.

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In my experience, one of the hardest parts of being a sysadmin is patching systems. Every time you get a Common Vulnerabilities and Exposure (CVE) notification or Information Assurance Vulnerability Alert (IAVA) mandated by security, you have to kick into high gear to close the security gaps. (And, believe me, your security officer will hunt you down unless the vulnerabilities are patched.)

Ansible can reduce the time it takes to patch systems by running packaging modules. To demonstrate, let's use the yum module to update the system. Ansible can install, update, remove, or install from another location (e.g., rpmbuild from continuous integration/continuous development). Here is the task for updating the system:

  - name: update the system
    yum:
      name: "*"
      state: latest

In the first line, we give the task a meaningful name so we know what Ansible is doing. In the next line, the yum module updates the CentOS virtual machine (VM), then name: "*" tells yum to update everything, and, finally, state: latest updates to the latest RPM.

After updating the system, we need to restart and reconnect:

  - name: restart system to reboot to newest kernel
    shell: "sleep 5 && reboot"
    async: 1
    poll: 0

  - name: wait for 10 seconds
    pause:
      seconds: 10

  - name: wait for the system to reboot
    wait_for_connection:
      connect_timeout: 20
      sleep: 5
      delay: 5
      timeout: 60

  - name: install epel-release
    yum:
      name: epel-release
      state: latest

The shell module puts the system to sleep for 5 seconds then reboots. We use sleep to prevent the connection from breaking, async to avoid timeout, and poll to fire & forget. We pause for 10 seconds to wait for the VM to come back and use wait_for_connection to connect back to the VM as soon as it can make a connection. Then we install epel-release to test the RPM installation. You can run this playbook multiple times to show the idempotent, and the only task that will show as changed is the reboot since we are using the shell module. You can use changed_when: False to ignore the change when using the shell module if you expect no actual changes.

So far we've learned how to update a system, restart the VM, reconnect, and install a RPM. Next we will install NGINX using the role in Ansible Lightbulb.

  - name: Ensure nginx packages are present
    yum:
      name: nginx, python-pip, python-devel, devel
      state: present
    notify: restart-nginx-service

  - name: Ensure uwsgi package is present
    pip:
      name: uwsgi
      state: present
    notify: restart-nginx-service

  - name: Ensure latest default.conf is present
    template:
      src: templates/nginx.conf.j2
      dest: /etc/nginx/nginx.conf
      backup: yes
    notify: restart-nginx-service

  - name: Ensure latest index.html is present
    template:
      src: templates/index.html.j2
      dest: /usr/share/nginx/html/index.html

  - name: Ensure nginx service is started and enabled
    service:
      name: nginx
      state: started
      enabled: yes

  - name: Ensure proper response from localhost can be received
    uri:
      url: "http://localhost:80/"
      return_content: yes
    register: response
    until: 'nginx_test_message in response.content'
    retries: 10
    delay: 1

And the handler that restarts the nginx service:

# handlers file for nginx-example
  - name: restart-nginx-service
    service:
      name: nginx
      state: restarted

In this role, we install the RPMs nginx, python-pip, python-devel, and devel and install uwsgi with PIP. Next, we use the template module to copy over the nginx.conf and index.html for the page to display. After that, we make sure the service is enabled on boot and started. Then we use the uri module to check the connection to the page.

Here is a playbook showing an example of updating, restarting, and installing an RPM. Then continue installing nginx. This can be done with any other roles/applications you want.

  - hosts: all
    roles:
      - centos-update
      - nginx-simple

Watch this demo video for more insight on the process.

This was just a simple example of how to update, reboot, and continue. For simplicity, I added the packages without variables. Once you start working with a large number of hosts, you will need to change a few settings:

• async & poll
• serial
• forks

This is because on your production environment you might want to update one system at a time (not fire & forget) and actually wait a longer time for your system to reboot and continue.

For more ways to automate your work with this tool, take a look at the other Ansible articles on Opensource.com.