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
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
devel and install
uwsgi with PIP. Next, we use the
template module to copy over the
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:
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.