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Host Group Vars

Right now, both my EC2 machine and my virtual machine are configured to respond to mootube.l. And that means I can only access one at a time: I can setup my /etc/hosts to make mootube.l point to my EC2 instance or my VM... but not both.

What if instead, we setup the VM to be mootube.l and the EC2 instance to be mootube.ec2? That would fix it! How can we do that?

The problem is that in our roles/nginx/vars/main.yml file, we have a server_name variable... but it's just hardcoded to mootube.l:

3 lines ansible/roles/nginx/vars/main.yml
---
server_name: mootube.l

I want to override that variable to a different value for each host group. And that is totally possible.

But first, re-open /etc/hosts and point mootube.l back to the virtual machine IP. Then, add a new mootube.ec2 entry that points to the EC2 instance:

sudo vim /etc/hosts
# /etc/hosts
# ...
192.168.33.10 mootube.l
54.205.128.194 mootube.ec2

Nice!

Setting Variables for a Host Group

Now, how can we override the server_name variable only for the aws host group? Create a new directory called group_vars with a file inside: aws.yml. Just by having this exact directory and filename, whenever the aws group is executed, it will automatically load this file and use the variables inside. But those variables will only apply to the aws group.

Inside, create a new host_server_name variable set to mootube.ec2:

3 lines ansible/group_vars/aws.yml
---
host_server_name: ec2-54-205-128-194.compute-1.amazonaws.com

Copy that variable name. Next, open roles/nginx/vars/main.yml, replace the hardcoded mootube.l with something fancier: {{ host_server_name|default('mootube.l') }}:

3 lines ansible/roles/nginx/vars/main.yml
---
server_name: "{{ host_server_name|default('mootube.l') }}"

This says: use host_server_name if it exists. But if it doesn't, default to mootube.l. This should give us a unique host_name variable for each group.

We're ready: try the playbook:

ansible-playbook ansible/playbook.yml -i ansible/hosts.ini --ask-vault-pass

Nice - we can see a few changes, but only to the EC2 server, as it changes the host name. Ding!

Go back to your browser and refresh mootube.l. This is coming from the VM: I know because it has data! Now try http://mootube.ec2. Boom! This comes from EC2. Super fun.

We just used Ansible to provision an entirely new server on EC2. Could we even use it to launch the server programmatically? Nope! I'm kidding - totally - let's do it!

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