Typically, with Ansible you create one or more hosts file which it calls Inventory file and Ansible will pick the servers from the hosts file and runs the playbooks onto the servers. This is a simple and straightforward way to do it. However, if you are using the Cloud, its very likely that your applications are creating and deleting servers based on some other logic and its very impractical to maintain a static Inventory file. In that case, Ansible can directly talk to your cloud (AWS, Rackspace, OpenStack, etc) or a dynamic source (Cobbler etc) through what it calls Dynamic Inventory plugins, without you having to maintain a static list of servers.
Here, I will go through the process of using the Rackspace Public Cloud Dynamic Inventory Plugin with Ansible.
First of all, if you have not already installed Ansible, go ahead and do so. I like to install Ansible within virtualenv using pip.
sudo apt-get update sudo apt-get upgrade sudo apt-get install python-dev python-virtualenv virtualenv env source env/bin/activate pip install ansible
Install Rax Dynamic Inventory Plugin
Ansible maintains an external RAX Inventory File on its repository (Not sure why these plugins do not get bundled with the Ansible package). The rax.py script depends on pyrax module, which is the client binding for Rackspace Cloud.
pip install pyrax wget https://raw.github.com/ansible/ansible/devel/plugins/inventory/rax.py chmod +x rax.py
The script needs a configuration file named ~/.rackspace_cloud_credentials, which will store your auth credentials to Rackspace Cloud.
cat ~/.rackspace_cloud_credentials [rackspace_cloud] username = <username> api_key = <apikey>
As you can see, rax.py is a very simple script that provides a couple of methods to list and show servers in your cloud. By default, it grabs the servers in all Rackspace regions. If you are interested in only one region, you can specify the RAX_REGION.
./rax.py --list RAX_REGION=DFW ./rax.py --list RAX_REGION=DFW ./rax.py --host some-cloud-server
Create Cloud Servers
Since you have already pyrax installed as a dependency of rax.py inventory plugin, you can use command-line to create a cloud server named ‘staging-apache1′ and and tag the server as staging-apache group using the metadata key-value feature.
export OS_USERNAME=<username> export OS_PASSWORD=<apikey> export OS_TENANT_NAME=<username> export OS_AUTH_SYSTEM=rackspace export OS_REGION_NAME=DFW export OS_AUTH_URL=https://identity.api.rackspacecloud.com/v2.0/ ssh-keygen nova keypair-add --pub-key ~/.ssh/id_rsa.pub stagingkey nova boot --image 80fbcb55-b206-41f9-9bc2-2dd7aac6c061 --flavor 2 --meta group=staging-apache --key-name stagingkey staging-apache1
If you want to install Apache on more staging servers, you would create server named staging-apache2 and tag it with the same group name staging-apache.
Also note, we are injecting ssh keys to the servers on creation, so ansible will be able to do ssh passwordless login. With Ansible, you also have the option of using username-password if you choose so.
Once the server is booted, lets make sure ansible can ping all the servers tagged with the group staging-apache.
ansible -i rax.py staging-apache -u root -m ping
Run a sample playbook
Now, lets create a very simple playbook to install apache on the inventory.
$ cat apache.yml - hosts: staging-apache tasks: - name: Installs apache web server apt: pkg=apache2 state=installed update_cache=true
Lets run the apache playbook on all rax servers in the region DFW and that match the hosts in the group staging-apache.
RAX_REGION=DFW ansible-playbook -i rax.py apache.yml
With static inventory, you’d be doing this instead, and manually updating the hosts file:
ansible-playbook -i hosts apache.yml
Now you can ssh into the staging-apache1 server and make sure everything is configured as per your playbook.
ssh -i ~/.ssh/id_rsa root@staging-apache1
You may add more servers to the staging-apache group, and on the next run, ansible will detect the updated inventory dynamically and run the playbooks.
Rackspace Public Cloud is based off of OpenStack Nova. So nova.py inventory should work pretty much the same. You can look at the complete lists of dynamic inventory plugins here. Adding a new inventory plugin like for say Razor that isn’t already there would be fairly simple.