With version 3.1 Ansible Tower introduced clustering, replacing the redundancy solution configured with active-passive nodes. Clustering is sharing load between Tower nodes/instances. Each Tower instance is able to act as an entry point for UI and API access.
Using a load balancer in front of the Tower nodes is possible, but optional because an Ansible Tower cluster can be accessed via all Tower instances.
Each instance in a Tower cluster expands the cluster’s capacity to execute jobs. Jobs can and will run anywhere rather than be directed on where to run.
The Appendix contains some installation considerations and an installer inventory for reference.
For the first contact to your cluster open your browser and login to the Tower node 1 web UIs as:
user admin
password VERY_SECRET_PASSWORD
Use the pre-created URLs from the lab landing page or replace <LABID> with the session ID and <N> with your student number!
https://student<N>.<LABID>.open.redhat.com
Just from the web UI you wouldn’t know you’ve got a Tower cluster at your hands here. To learn more about your cluster and its state, in one of the instances web UI under ADMINISTRATION choose Instance Groups. Here you will get an overview of the cluster by instance groups. Explore the information provided, of course there is no capacity used yet and no Jobs have run.
Right now we have only one instance group named tower. When you get more groups, from this view you will see how the instance are distributed over the groups.
To dig deeper click on INSTANCES to get more information about the instances allocated to a group. In the instances view you can toggle nodes off/online and adjust the number of forks (don’t do this now).
You’ll learn more about this later.
You can also get information about your cluster on the command line. Log in to your code-server again if you closed it by opening this URL in your browser:
https://student<N>-code.<LABID>.open.redhat.com
Your VSCode session is running on your Tower node 1. Again if not still open, open a terminal by clicking Terminal->New Terminal in the menu bar.
A terminal window opens at the bottom, become root:
[student@ansible-1 ~]$ sudo -i
[root@ansible-1 ~]#
In the terminal run the following command:
Your exact hostnames will differ, of course!
[root@ansible-1 ~]# awx-manage list_instances
[tower capacity=51]
ansible-1 capacity=17 version=3.7.1 heartbeat="2020-08-27 09:06:21"
ansible-2 capacity=17 version=3.7.1 heartbeat="2020-08-27 09:05:58"
ansible-3 capacity=17 version=3.7.1 heartbeat="2020-08-27 09:06:00"
So what we’ve got is a three-node Tower cluster, no surprises here. In addition the command tells us the capacity (maximum number of forks/concurrent jobs) per node and for the instance groups. Here the capacity value of 17 is allocated to any of our three nodes.
The awx-manage (formerly tower-manage) utility can be used to manage a lot of the more internal aspects of Tower. You can e.g. use it to clean up old data, for token and session management and for cluster management.