Google Cloud Platform Guide

Introduction

Ansible contains modules for managing Google Compute Engine resources, including creating instances, controlling network access, working with persistent disks, and managing load balancers. Additionally, there is an inventory plugin that can automatically suck down all of your GCE instances into Ansible dynamic inventory, and create groups by tag and other properties.

The GCE modules all require the apache-libcloud module which you can install from pip:

$ pip install apache-libcloud

Credentials

To work with the GCE modules, you’ll first need to get some credentials in the JSON format:

1. Create a Service Account
2. Download JSON credentials

There are three different ways to provide credentials to Ansible so that it can talk with Google Cloud for provisioning and configuration actions:

• by providing to the modules directly
• by populating a secrets.py file
• by setting environment variables

Calling Modules By Passing Credentials

For the GCE modules you can specify the credentials as arguments:

• service_account_email: email associated with the project
• credentials_file: path to the JSON credentials file
• project_id: id of the project

For example, to create a new instance using the cloud module, you can use the following configuration:

- name: Create instance(s)
  hosts: localhost
  connection: local
  gather_facts: no

  vars:
    service_account_email: [email protected]
    credentials_file: /path/to/project.json
    project_id: project-id
    machine_type: n1-standard-1
    image: debian-7

  tasks:

   - name: Launch instances
     gce:
         instance_names: dev
         machine_type: "{{ machine_type }}"
         image: "{{ image }}"
         service_account_email: "{{ service_account_email }}"
         credentials_file: "{{ credentials_file }}"
         project_id: "{{ project_id }}"

When running Ansible inside a GCE VM you can use the service account credentials from the local metadata server by setting both service_account_email and credentials_file to a blank string.

Configuring Modules with secrets.py

Create a file secrets.py looking like following, and put it in some folder which is in your $PYTHONPATH:

GCE_PARAMS = ('[email protected]', '/path/to/project.json')
GCE_KEYWORD_PARAMS = {'project': 'project_id', 'datacenter': 'gce_zone'}

Ensure to enter the email address from the created services account and not the one from your main account.

Now the modules can be used as above, but the account information can be omitted.

If you are running Ansible from inside a GCE VM with an authorized service account you can set the email address and credentials path as follows so that get automatically picked up:

GCE_PARAMS = ('', '')
GCE_KEYWORD_PARAMS = {'project': 'project_id', 'datacenter': ''}

Configuring Modules with Environment Variables

Set the following environment variables before running Ansible in order to configure your credentials:

GCE_EMAIL
GCE_PROJECT
GCE_CREDENTIALS_FILE_PATH

GCE Dynamic Inventory

The best way to interact with your hosts is to use the gce inventory plugin, which dynamically queries GCE and tells Ansible what nodes can be managed.

Note that when using the inventory script gce.py, you also need to populate the gce.ini file that you can find in the contrib/inventory directory of the ansible checkout.

To use the GCE dynamic inventory script, copy gce.py from contrib/inventory into your inventory directory and make it executable. You can specify credentials for gce.py using the GCE_INI_PATH environment variable – the default is to look for gce.ini in the same directory as the inventory script.

Let’s see if inventory is working:

$ ./gce.py --list

You should see output describing the hosts you have, if any, running in Google Compute Engine.

Now let’s see if we can use the inventory script to talk to Google.

$ GCE_INI_PATH=~/.gce.ini ansible all -i gce.py -m setup
hostname | success >> {
  "ansible_facts": {
    "ansible_all_ipv4_addresses": [
      "x.x.x.x"
    ],

As with all dynamic inventory scripts in Ansible, you can configure the inventory path in ansible.cfg. The recommended way to use the inventory is to create an inventory directory, and place both the gce.py script and a file containing localhost in it. This can allow for cloud inventory to be used alongside local inventory (such as a physical datacenter) or machines running in different providers.

Executing ansible or ansible-playbook and specifying the inventory directory instead of an individual file will cause ansible to evaluate each file in that directory for inventory.

Let’s once again use our inventory script to see if it can talk to Google Cloud:

$ ansible all -i inventory/ -m setup
hostname | success >> {
  "ansible_facts": {
    "ansible_all_ipv4_addresses": [
        "x.x.x.x"
    ],

The output should be similar to the previous command. If you’re wanting less output and just want to check for SSH connectivity, use “-m” ping instead.

Use Cases

For the following use case, let’s use this small shell script as a wrapper.

#!/usr/bin/env bash
PLAYBOOK="$1"

if [[ -z $PLAYBOOK ]]; then
  echo "You need to pass a playbook as argument to this script."
  exit 1
fi

export SSL_CERT_FILE=$(pwd)/cacert.pem
export ANSIBLE_HOST_KEY_CHECKING=False

if [[ ! -f "$SSL_CERT_FILE" ]]; then
  curl -O http://curl.haxx.se/ca/cacert.pem
fi

ansible-playbook -v -i inventory/ "$PLAYBOOK"

Create an instance

The GCE module provides the ability to provision instances within Google Compute Engine. The provisioning task is typically performed from your Ansible control server against Google Cloud’s API.

A playbook would looks like this:

- name: Create instance(s)
  hosts: localhost
  gather_facts: no
  connection: local

  vars:
    machine_type: n1-standard-1 # default
    image: debian-7
    service_account_email: [email protected]
    credentials_file: /path/to/project.json
    project_id: project-id

  tasks:
    - name: Launch instances
      gce:
          instance_names: dev
          machine_type: "{{ machine_type }}"
          image: "{{ image }}"
          service_account_email: "{{ service_account_email }}"
          credentials_file: "{{ credentials_file }}"
          project_id: "{{ project_id }}"
          tags: webserver
      register: gce

    - name: Wait for SSH to come up
      wait_for: host={{ item.public_ip }} port=22 delay=10 timeout=60
      loop: "{{ gce.instance_data }}"

    - name: Add host to groupname
      add_host: hostname={{ item.public_ip }} groupname=new_instances
      loop: "{{ gce.instance_data }}"

- name: Manage new instances
  hosts: new_instances
  connection: ssh
  sudo: True
  roles:
    - base_configuration
    - production_server

Note that use of the “add_host” module above creates a temporary, in-memory group. This means that a play in the same playbook can then manage machines in the ‘new_instances’ group, if so desired. Any sort of arbitrary configuration is possible at this point.

Configuring instances in a group

All of the created instances in GCE are grouped by tag. Since this is a cloud, it’s probably best to ignore hostnames and just focus on group management.

Normally we’d also use roles here, but the following example is a simple one. Here we will also use the “gce_net” module to open up access to port 80 on these nodes.

The variables in the ‘vars’ section could also be kept in a ‘vars_files’ file or something encrypted with Ansible-vault, if you so choose. This is just a basic example of what is possible:

- name: Setup web servers
  hosts: tag_webserver
  gather_facts: no

  vars:
    machine_type: n1-standard-1 # default
    image: debian-7
    service_account_email: [email protected]
    credentials_file: /path/to/project.json
    project_id: project-id

  roles:

    - name: Install lighttpd
      apt: pkg=lighttpd state=installed
      sudo: True

    - name: Allow HTTP
      local_action: gce_net
      args:
        fwname: "all-http"
        name: "default"
        allowed: "tcp:80"
        state: "present"
        service_account_email: "{{ service_account_email }}"
        credentials_file: "{{ credentials_file }}"
        project_id: "{{ project_id }}"

By pointing your browser to the IP of the server, you should see a page welcoming you.

Upgrades to this documentation are welcome, hit the github link at the top right of this page if you would like to make additions!