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Using Ansible to Launch Instances on OpenStack

This is a short tutorial on how to deploy instances onto OpenStack clouds using Ansible. It assumes familiarity with the Ansible Playbook Introduction. Start there if you haven't written an Ansible playbook before. The goal of this tutorial is to launch and configure an instance on an OpenStack platform. It assumes that the instance does not exist in the current inventory of the Ansible host.

Start simple.

We'll begin with a simple playbook that has a single play - a simplified version of the webserver example in the Ansible Playbook Introduction. This play follows.

- hosts: webservers
  remote_user: centos
  sudo: yes
  tasks:
    - name: ensure apache is at the latest version
      yum: name=httpd state=latest
    - name: make sure apache is running
      service: name=httpd state=running

We're running two tasks in this play - one to install apache and one to start it and enable it. We're also specifying that this play should be run against any hosts in the webservers group and should be run as the centos user.

To run the first play, manually launch a CentOS image in your OpenStack tenant and assign a floating IP to it. Then create a simple hosts file with the floating IP listed in the "webservers" group:

[webservers]
<floating_ip>

Run the example playbook like so:

$ ansible-playbook -i hosts webserver.yml

You should see that the tasks succeed and that the Apache HTTP Server is installed and running on the instance. If they don't, check that you've got your SSH keys configured correctly, the instance can access the Internet to download packages, you have connectivity to the instance, and so on.

Launching an Instance

Next we'll launch an instance in an Ansible task. We'll be using the new os_server module available in Ansible 2.0.

The following play demonstrates basic usage of the os_server module.

- name: Deploy on OpenStack
  hosts: localhost
  gather_facts: false
  tasks:
  - name: Deploy an instance
    os_server:
      state: present
      name: webserver
      image: centos-7-x86_64-genericcloud
      key_name: root
      wait: yes
      flavor: m1.small
      auto_floating_ip: yes
      network: private
      meta:
        hostname: webserver.localdomain

There are a couple of things to note with this example. The first is that every task in Ansible needs to run on some host. The os_server task is typically a "local action", but doesn't have to be. Whichever machine you're going to run the task on needs to have the Python Shade library installed (https://pypi.python.org/pypi/shade). Second, we're turning off fact gathering. This also isn't necessary, but speeds up the execution quite a bit. Also consider specifying that your connection to localhost is local with a line like the following in your ansible hosts file:

localhost        ansible_connection=local

The task itself is pretty simple. It contains all of the variables that you would expect to specify to launch an instance. Before we edit and run the playbook, we'll need to source in an OpenStack RC file which contains the authentication information for our user and tenant. This RC file can be downloaded from Horizon under the "Access & Security" tab, if you don't already have one.

Once we've sourced in the OpenStack RC file, we'll edit the playbook to match our environment and then we'll run the playbook like so:

$ . ./openrc.sh
$ ansible-playbook openstack_deploy.yaml

Assuming that you've specified the correct network name, image name, key name, and so on, you should see the following output and have an instance named "webserver" running in your tenant now.

PLAY [Deploy on OpenStack] **************************************************** 

TASK: [Deploy an instance] **************************************************** 
changed: [localhost]

PLAY RECAP ******************************************************************** 
localhost                  : ok=1    changed=1    unreachable=0    failed=0

Note that the os_server module is idempotent. Running this playbook multiple times will not launch multiple instances. Also note that the instance can be terminated by changing the "state" attribute from "present" to "absent" and running the playbook.

Putting it all together.

Now that we can launch an instance in OpenStack, the next logical step is to configure it. First, we'll use the add_host module to add the provisioned instance into the Ansible inventory after we provision it. This is a little complicated, but we can't really know what the floating IP of the instance will be until we've provisioned it, so we can't add it to the inventory before we run the playbook. The example follows.

---
- name: Deploy on OpenStack
  hosts: localhost
  gather_facts: false
  tasks:
  - name: Deploy an instance
    os_server:
      state: present
      name: webserver
      image: centos-7-x86_64-genericcloud
      key_name: root
      wait: yes
      flavor: m1.small
      auto_floating_ip: yes
      network: private
      meta:
        hostname: webserver.localdomain
    register: webserver

  - name: Wait for SSH on the Instance
    command: >
      ssh -oBatchMode=yes -oStrictHostKeyChecking=no
      centos@{{webserver.server.public_v4}} true
    register: result
    until: result|success
    retries: 30
    delay: 10
  
  - name: Add CentOS Instance to Inventory
    add_host: name=webserver groups=webservers
              ansible_ssh_host={{ webserver.server.public_v4 }} 
  
- hosts: webservers
  remote_user: centos
  sudo: yes
  tasks:
    - name: ensure apache is at the latest version
      yum: name=httpd state=latest
    - name: make sure apache is running
      service: name=httpd state=running

Once again, modify the attributes in the os_server task to match your environment. These task is the same as the one we used in the last section, except that we're now registering the output of the task so that we can access the floating IP address of the instance as a variable. We add the host to our in-memory inventory in the third task. We've also added a second task which waits until SSH is available on the host for us to continue playbook execution.

The last play in the playbook is the same the play that we started the tutorial with. It installs and starts apache on all of the webservers, which now includes the instance that we provisioned on OpenStack. Run this example the same way as the last one:

$ . ./openrc.sh
$ ansible-playbook openstack_webserver.yaml

You should get some output similar to the following:

PLAY [Deploy on OpenStack] **************************************************** 

TASK: [Deploy an instance] **************************************************** 
ok: [localhost]

TASK: [Add CentOS Instance to Inventory] ************************************** 
ok: [localhost]

PLAY [webservers] ************************************************************* 

GATHERING FACTS *************************************************************** 
ok: [webserver]

TASK: [ensure apache is at the latest version] ******************************** 
changed: [webserver]

TASK: [make sure apache is running] ******************************************* 
changed: [webserver]

PLAY RECAP ******************************************************************** 
localhost                  : ok=2    changed=0    unreachable=0    failed=0   
webserver                  : ok=3    changed=2    unreachable=0    failed=0

Note that there are now two hosts which are listed in the Play recap - the plays which launch the instance are run on localhost and the plays which configure the webserver are run on the provisioned instance.