If your Ansible inventory fluctuates over time, with hosts spinning up and shutting down in response to business demands, the static inventory solutions described in :ref:`inventory` will not serve your needs. You may need to track hosts from multiple sources: cloud providers, LDAP, `Cobbler <https://cobbler.github.io>`_, and/or enterprise CMDB systems.
Ansible integrates all of these options via a dynamic external inventory system. Ansible supports two ways to connect with external inventory: :ref:`inventory_plugins` and `inventory scripts <https://github.com/ansible/ansible/tree/devel/contrib/inventory>`.
Inventory plugins take advantage of the most recent updates to Ansible's core code. We recommend plugins over scripts for dynamic inventory. You can :ref:`write your own plugin <developing_inventory>` to connect to additional dynamic inventory sources.
You can still use inventory scripts if you choose. When we implemented inventory plugins, we ensured backwards compatibility via the script inventory plugin. The examples below illustrate how to use inventory scripts.
If you'd like a GUI for handling dynamic inventory, the :ref:`ansible_tower` inventory database syncs with all your dynamic inventory sources, provides web and REST access to the results, and offers a graphical inventory editor. With a database record of all of your hosts, you can correlate past event history and see which hosts have had failures on their last playbook runs.
Ansible integrates seamlessly with `Cobbler <https://cobbler.github.io>`_, a Linux installation server originally written by Michael DeHaan and now led by James Cammarata, who works for Ansible.
To tie Ansible's inventory to Cobbler, copy `this script <https://raw.githubusercontent.com/ansible/ansible/devel/contrib/inventory/cobbler.py>`_ to ``/etc/ansible`` and ``chmod +x`` the file. Run ``cobblerd`` any time you use Ansible and use the ``-i`` command line option (e.g. ``-i /etc/ansible/cobbler.py``) to communicate with Cobbler using Cobbler's XMLRPC API.
First test the script by running ``/etc/ansible/cobbler.py`` directly. You should see some JSON data output, but it may not have anything in it just yet.
In the example above, the system 'foo.example.com' will be addressable by ansible directly, but will also be addressable when using the group names 'webserver' or 'atlanta'. Since Ansible uses SSH, we'll try to contact system foo over 'foo.example.com', only, never just 'foo'. Similarly, if you try "ansible foo" it wouldn't find the system... but "ansible 'foo*'" would, because the system DNS name starts with 'foo'.
The script doesn't just provide host and group info. In addition, as a bonus, when the 'setup' module is run (which happens automatically when using playbooks), the variables 'a', 'b', and 'c' will all be auto-populated in the templates::
# file: /srv/motd.j2
Welcome, I am templated with a value of a={{ a }}, b={{ b }}, and c={{ c }}
Which could be executed just like this::
ansible webserver -m setup
ansible webserver -m template -a "src=/tmp/motd.j2 dest=/etc/motd"
If you use Amazon Web Services EC2, maintaining an inventory file might not be the best approach, because hosts may come and go over time, be managed by external applications, or you might even be using AWS autoscaling. For this reason, you can use the `EC2 external inventory <https://raw.githubusercontent.com/ansible/ansible/devel/contrib/inventory/ec2.py>`_ script.
The second option is to copy the script to `/etc/ansible/hosts` and `chmod +x` it. You will also need to copy the `ec2.ini <https://raw.githubusercontent.com/ansible/ansible/devel/contrib/inventory/ec2.ini>`_ file to `/etc/ansible/ec2.ini`. Then you can run ansible as you would normally.
To successfully make an API call to AWS, you will need to configure Boto (the Python interface to AWS). There are a `variety of methods <http://docs.pythonboto.org/en/latest/boto_config_tut.html>`_ available, but the simplest is just to export two environment variables::
If you use Boto profiles to manage multiple AWS accounts, you can pass ``--profile PROFILE`` name to the ``ec2.py`` script. An example profile might be::
Since each region requires its own API call, if you are only using a small set of regions, you can edit the ``ec2.ini`` file and comment out the regions you are not using.
There are other config options in ``ec2.ini``, including cache control and destination variables. By default, the ``ec2.ini`` file is configured for **all Amazon cloud services**, but you can comment out any features that aren't applicable. For example, if you don't have ``RDS`` or ``elasticache``, you can set them to ``False`` ::
At their heart, inventory files are simply a mapping from some name to a destination address. The default ``ec2.ini`` settings are configured for running Ansible from outside EC2 (from your laptop for example) -- and this is not the most efficient way to manage EC2.
If you are running Ansible from within EC2, internal DNS names and IP addresses may make more sense than public DNS names. In this case, you can modify the ``destination_variable`` in ``ec2.ini`` to be the private DNS name of an instance. This is particularly important when running Ansible within a private subnet inside a VPC, where the only way to access an instance is via its private IP address. For VPC instances, `vpc_destination_variable` in ``ec2.ini`` provides a means of using which ever `boto.ec2.instance variable <http://docs.pythonboto.org/en/latest/ref/ec2.html#module-boto.ec2.instance>`_ makes the most sense for your use case.
The EC2 external inventory provides mappings to instances from several groups:
Instances belong to one or more security groups. A group is created for each security group, with all characters except alphanumerics, converted to underscores (_). Each group is prefixed by ``security_group_``. Currently, dashes (-) are also converted to underscores (_). You can change using the replace_dash_in_groups setting in ec2.ini (this has changed across several versions so check the ec2.ini for details).
Each instance can have a variety of key/value pairs associated with it called Tags. The most common tag key is 'Name', though anything is possible. Each key/value pair is its own group of instances, again with special characters converted to underscores, in the format ``tag_KEY_VALUE``
When the Ansible is interacting with a specific server, the EC2 inventory script is called again with the ``--host HOST`` option. This looks up the HOST in the index cache to get the instance ID, and then makes an API call to AWS to get information about that specific instance. It then makes information about that instance available as variables to your playbooks. Each variable is prefixed by ``ec2_``. Here are some of the variables available:
- ec2_architecture
- ec2_description
- ec2_dns_name
- ec2_id
- ec2_image_id
- ec2_instance_type
- ec2_ip_address
- ec2_kernel
- ec2_key_name
- ec2_launch_time
- ec2_monitored
- ec2_ownerId
- ec2_placement
- ec2_platform
- ec2_previous_state
- ec2_private_dns_name
- ec2_private_ip_address
- ec2_public_dns_name
- ec2_ramdisk
- ec2_region
- ec2_root_device_name
- ec2_root_device_type
- ec2_security_group_ids
- ec2_security_group_names
- ec2_spot_instance_request_id
- ec2_state
- ec2_state_code
- ec2_state_reason
- ec2_status
- ec2_subnet_id
- ec2_tag_Name
- ec2_tenancy
- ec2_virtualization_type
- ec2_vpc_id
Both ``ec2_security_group_ids`` and ``ec2_security_group_names`` are comma-separated lists of all security groups. Each EC2 tag is a variable in the format ``ec2_tag_KEY``.
To see the complete list of variables available for an instance, run the script by itself::
If you use an OpenStack-based cloud, instead of manually maintaining your own inventory file, you can use the ``openstack_inventory.py`` dynamic inventory to pull information about your compute instances directly from OpenStack.
You can download the latest version of the OpenStack inventory script `here <https://raw.githubusercontent.com/ansible/ansible/devel/contrib/inventory/openstack_inventory.py>`_.
You can use the inventory script explicitly (by passing the `-i openstack_inventory.py` argument to Ansible) or implicitly (by placing the script at `/etc/ansible/hosts`).
An OpenStack RC file contains the environment variables required by the client tools to establish a connection with the cloud provider, such as the authentication URL, user name, password and region name. For more information on how to download, create or source an OpenStack RC file, please refer to `Set environment variables using the OpenStack RC file <https://docs.openstack.org/user-guide/common/cli_set_environment_variables_using_openstack_rc.html>`_.
The OpenStack command line clients are required to run the `nova list` command. For more information on how to install them, please refer to `Install the OpenStack command-line clients <https://docs.openstack.org/user-guide/common/cli_install_openstack_command_line_clients.html>`_.
Once you confirm the dynamic inventory script is working as expected, you can tell Ansible to use the `openstack_inventory.py` script as an inventory file, as illustrated below::
Note that the OpenStack dynamic inventory script will cache results to avoid repeated API calls. To explicitly clear the cache, you can run the openstack_inventory.py (or hosts) script with the ``--refresh`` parameter::
You can find all included inventory scripts in the `contrib/inventory directory <https://github.com/ansible/ansible/tree/devel/contrib/inventory>`_. General usage is similar across all inventory scripts. You can also :ref:`write your own inventory script <developing_inventory>`.
In an inventory directory, executable files will be treated as dynamic inventory sources and most other files as static sources. Files which end with any of the following will be ignored::
You can replace this list with your own selection by configuring an ``inventory_ignore_extensions`` list in ansible.cfg, or setting the :envvar:`ANSIBLE_INVENTORY_IGNORE` environment variable. The value in either case should be a comma-separated list of patterns, as shown above.
Any ``group_vars`` and ``host_vars`` subdirectories in an inventory directory will be interpreted as expected, making inventory directories a powerful way to organize different sets of configurations. See :ref:`using_multiple_inventory_sources` for more information.
