In the previous lab, we created two WildFly Swarm servers running our application. The next step is to setup a load balancer. We will use NGINX as the load balancer in this lab. Let's overview which part of the system you will be working on.
A role has already been written for installing NGINX with Ansible. The role can be found at the Ansible Galaxy site (https://galaxy.ansible.com/nginxinc/nginx/). Ansible Galaxy is the place where roles and modules are shared.
👍 As always be critical when using content on the internet. When it comes to roles on Ansible Galaxy it's easy to do a quick review of the general health of the role.
👍 Look at development activity of the role and number of downloads. Ansible Galaxy makes this evaluation easy by putting it on the front page of each role, as marked above. If there is not a lot of activity, there may be a risk that the role is not maintained.
💥 Now that we've seen that the nginx role seems solid. We need to install the role. First create file for pulling required roles with ansible-galaxy:
cat << 'EOF' > $WORK_DIR/requirements.yml
- src: nginxinc.nginx
name: nginx
EOF
And do run the install command to pull all required external roles:
ansible-galaxy install --roles-path=$WORK_DIR/roles -r requirements.yml
and wait for the role to be installed. When that is done, we can use the role in our playbooks.
💥 To create a playbook which installs NGINX go to $WORK_DIR and create a new file named lb.yml with the following content:
---
- name: Install NGINX
hosts: lbservers
become: true
tasks:
- include_role:
name: nginx
💥 Now, run the playbook to install NGINX on your server in the lbservers group with the command
ansible-playbook -i hosts lb.yml
Take a moment to appreciate how simple that was. You can again run the playbook multiple times, to ensure that this role is idempotent and that nothing changes the second time you run it.
This installs NGINX on the servers in the lbservers group.
💥 To verify the installation, in your web browser, go to: http://$loadbalancer1-ip-address.
You should get the NGINX default page, as shown above. Take some extra time to appreciate how very simple it was to install the NGINX software, even though you may never have done that before.
Next step is to configure NGINX as a loadbalancer for the two wildflyapp servers. To do so, we'll add an additional role for the configuration. We follow the best practises for Ansible directory layout and place tasks, handlers, and vars in separate directories. This is done so that it's easier to collaborate and maintain your work.
💥 To create a boilerplate for our new role, which features these best practices, we use the ansible-galaxy command. Run below commands:
cd $WORK_DIR
ansible-galaxy init roles/nginx-config
💥 First we'll create a handler for restarting the NGINX service in case of configuration changes. Define the handler in the file $WORK_DIR/roles/nginx-config/handlers/main.yml by replacing the content in the file with:
---
- name: restart-nginx-service
systemd:
state: restarted
daemon_reload: yes
name: nginx
💥 This defines a handler named restart-nginx-service, which we'll use in a moment. Now replace the content in the file $WORK_DIR/roles/nginx-config/tasks/main.yml with below:
---
- name: Configure NGINX to listen for http
template:
src: default.template
dest: /etc/nginx/conf.d/default.conf
notify: restart-nginx-service
- name: Ensure nginx is started and persistent across reboot
systemd:
name: nginx
enabled: yes
masked: no
state: started
- name: Set and persist httpd_can_network_connect SELinux flag for NGINX
seboolean:
name: httpd_can_network_connect
state: yes
persistent: yes
A template is used to setup the NGINX HTTP listener. The template ensures that your configuration file doesn't have to be static. In this case, you need to add the servers to loadbalance between. This is done by introducing a variable wildfly_servers, which you'll use when writing the template shortly. The configuration file is saved instead of the default.conf nginx template. Other approaches apply. Please refer to the NGINX documentation for more information. If the configuration file is changed, the previously defined handler (notify: restart-nginx-service) ensures that the NGINX process is restarted. Finally a SELinux rule has to be setup, to allow NGINX to connect to port 8080.
💥 Define the variable wildfly_servers by replacing $WORK_DIR/roles/nginx-config/vars/main.yml with below content:
---
wildfly_servers: "{{ groups['wildflyservers'] }}"
💥 Edit $WORK_DIR/lb.yml to include the newly created role. $WORK_DIR/lb.yml should now look as below:
---
- name: Install and configure NGINX as a load balancer
hosts: lbservers
become: true
tasks:
- include_role:
name: nginx
- include_role:
name: nginx-config
After having extended the playbook to add the loadbalancer configuration, you need to add the template file for the configuration.
💥 In your favorite editor create the file $WORK_DIR/roles/nginx-config/templates/default.template and add the following content:
upstream backend {
{% for host in wildfly_servers %}
server {{ hostvars[host].ansible_host }}:8080;
{% endfor %}
}
server {
listen 80;
server_name localhost;
access_log /var/log/nginx/host.access.log main;
location / {
proxy_pass http://backend;
}
# redirect server error pages to the static page /50x.html
#
error_page 500 502 503 504 /50x.html;
location = /50x.html {
root /usr/share/nginx/html;
}
}
As you can see, the wildfly_servers variable is used to iterate over the servers with the WildFly application deployed.
💥 Apply the changes to the NGINX configuration by running the playbook:
cd $WORK_DIR
ansible-playbook -i hosts lb.yml
The playbook should complete as such:
PLAY RECAP *****************************************************************
loadbalancer1 : ok=8 changed=3 unreachable=0 failed=0
💥 Now test, that you can access the application on both application servers. For this we'll use a simple http client, called curl. In your terminal write:
curl -w '\n' http://IP-address-of-loadbalancer1/
When running the command multiple times, you should see different wildfly servers responding, as shown below:
$ curl -w '\n' http://18.184.24.113/
Howdy from unknown at 2018-08-31T08:07:32.948Z (from ip-172-31-25-165.eu-central-1.compute.internal)
$ curl -w '\n' http://18.184.24.113/
Howdy from unknown at 2018-08-31T08:07:48.816Z (from ip-172-31-28-91.eu-central-1.compute.internal)
$
💥 Finally create a playbook to collect the two playbooks already made, by creating a file named main.yml in $WORK_DIR with the following content:
---
- import_playbook: lb.yml
- import_playbook: site.yml
💥 By running this playbook, you can setup everything with one command. Try it out.
ansible-playbook -i hosts main.yml
The playbook should complete as such:
PLAY RECAP ****************************************************************
loadbalancer1 : ok=7 changed=0 unreachable=0 failed=0
wildfly1 : ok=8 changed=0 unreachable=0 failed=0
wildfly2 : ok=8 changed=0 unreachable=0 failed=0
End of lab