Exercise 2.2 - Inventories, credentials and ad hoc commands

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Create an Inventory
Machine Credentials
Configure Machine Credentials
Run Ad Hoc Commands
Challenge Lab: Ad Hoc Commands

Create an Inventory

Let’s get started with: The first thing we need is an inventory of your managed hosts. This is the equivalent of an inventory file in Ansible Engine. There is a lot more to it (like dynamic inventories) but let’s start with the basics.

You should already have the web UI open, if not: Point your browser to the URL you were given, similar to https://student<X>.workshopname.rhdemo.io (replace “<X>” with your student number and “workshopname” with the name of your current workshop) and log in as admin. The password will be provided by the instructor.

Create the inventory:

In the web UI menu on the left side, go to RESOURCES → Inventories, click the button on the right side and choose Inventory.

Parameter	Value
NAME	Workshop Inventory
ORGANIZATION	Default

Click SAVE

Now there will be two inventories, the Demo Inventory and the Workshop Inventory. In the Workshop Inventory click the Hosts button, it will be empty since we have not added any hosts there.

So let’s add some hosts. First we need to have the list of all hosts which are accessible to you within this lab. These can be found in an inventory on the ansible control node on which Tower is installed. You’ll find the password for the SSH connection there as well.

Warning

Replace workshopname by the workshop name provided to you, and the X in studentX by the student number provided to you.

ssh student<X>@student<X>.workshopname.rhdemo.io

You can find the inventory information at ~/lab_inventory/hosts. Output them with cat, they should look like:

$ cat ~/lab_inventory/hosts
[all:vars]
ansible_user=student<X>
ansible_ssh_pass=PASSWORD
ansible_port=22

[web]
node1 ansible_host=22.33.44.55
node2 ansible_host=33.44.55.66
node3 ansible_host=44.55.66.77

[control]
ansible ansible_host=11.22.33.44

Warning

In your inventory the IP addresses will be different.

Note the names for the nodes and the IP addresses, we will use them to fill the inventory in Tower now:

In the inventory view of Tower click on your Workshop Inventory
Click on the HOSTS button
To the right click the button.
HOST NAME: node1
Variables: Under the three dashes ---, enter ansible_host: 22.33.44.55 in a new line. Make sure to enter your specific IP address for your node1 from the inventory looked up above, and note that the variable definition has a colon : and a space between the values, not an equal sign = like in the inventory file.
Click SAVE
Go back to HOSTS and repeat to add node2 as a second host and node3 as a third node. Make sure that for each node you enter the right IP addresses.

You have now created an inventory with three managed hosts.

Machine Credentials

One of the great features of Ansible Tower is to make credentials usable to users without making them visible. To allow Tower to execute jobs on remote hosts, you must configure connection credentials.

Note

This is one of the most important features of Tower: Credential Separation! Credentials are defined separately and not with the hosts or inventory settings.

As this is an important part of your Tower setup, why not make sure that connecting to the managed nodes from Tower is working?

To access the Tower host via SSH do the following:

Login to your Tower control host via SSH: ssh student<X>@student<X>.workshopname.rhdemo.io
Replace workshopname by the workshop name provided to you, and the <X> in student<X> by the student number provided to you.
From Tower SSH into node1 or one of the other nodes (look up the IP addresses from the inventory) and execute sudo -i.
For the SSH connection use the node password from the inventory file, sudo -i works without password.

[user@control ~]$ ssh student<X>@22.33.44.55
student<X>@22.33.44.55's password:
Last login: Thu Jul  4 14:47:04 2019 from 11.22.33.44
[student<X>@node1 ~]$ sudo -i
[root@node1 ~]#

What does this mean?

Tower user student<X> can connect to the managed hosts with password based SSH
User student<X> can execute commands on the managed hosts as root with sudo

Configure Machine Credentials

Now we will configure the credentials to access our managed hosts from Tower. In the RESOURCES menu choose Credentials. Now:

Click the plus button to add new credentials

NAME: Workshop Credentials
ORGANIZATION: Default
CREDENTIAL TYPE: Click on the magnifying glass, pick Machine and click
USERNAME: student<X> - make sure to replace the <X> with your actual student number!
PASSWORD: Enter the password from the inventory file.
PRIVILEGE ESCALATION METHOD: sudo
Click SAVE
Go back to the RESOURCES → Credentials → Workshop Credentials and note that the password is not visible.

Tip

Whenever you see a magnifiying glass icon next to an input field, clicking it will open a list to choose from.

You have now setup credentials to use later for your inventory hosts.

Run Ad Hoc Commands

As you’ve probably done with Ansible before you can run ad hoc commands from Tower as well.

In the web UI go to RESOURCES → Inventories → Workshop Inventory
Click the HOSTS button to change into the hosts view and select the three hosts by ticking the boxes to the left of the host entries.
Click RUN COMMANDS. In the next screen you have to specify the ad hoc command:
- As MODULE choose ping
- For MACHINE CREDENTIAL click the magnifying glass icon and select Workshop Credentials.
- Click LAUNCH, and watch the output.

The simple ping module doesn’t need options. For other modules you need to supply the command to run as an argument. Try the command module to find the userid of the executing user using an ad hoc command.

MODULE: command
ARGUMENTS: id

Tip

After choosing the module to run, Tower will provide a link to the docs page for the module when clicking the question mark next to “Arguments”. This is handy, give it a try.

How about trying to get some secret information from the system? Try to print out /etc/shadow.

MODULE: command
ARGUMENTS: cat /etc/shadow

Warning

Expect an error!

Oops, the last one didn’t went well, all red.

Re-run the last ad hoc command but this time tick the ENABLE PRIVILEGE ESCALATION box.

As you see, this time it worked. For tasks that have to run as root you need to escalate the privileges. This is the same as the become: yes you’ve probably used often in your Ansible Playbooks.

Challenge Lab: Ad Hoc Commands

Okay, a small challenge: Run an ad hoc to make sure the package “tmux” is installed on all hosts. If unsure, consult the documentation either via the web UI as shown above or by running [ansible@tower ~]$ ansible-doc yum on your Tower control host.

Warning

Solution below!

MODULE: yum
ARGUMENTS: name=tmux
Tick ENABLE PRIVILEGE ESCALATION

Tip

The yellow output of the command indicates Ansible has actually done something (here it needed to install the package). If you run the ad hoc command a second time, the output will be green and inform you that the package was already installed. So yellow in Ansible doesn’t mean “be careful”… ;-).

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