Ansible works against multiple managed nodes or "hosts" in your infrastructure at the same time, using a list or group of lists known as inventory. Once your inventory is defined, you use :ref:`patterns <intro_patterns>` to select the hosts or groups you want Ansible to run against.
The default location for inventory is a file called ``/etc/ansible/hosts``. You can specify a different inventory file at the command line using the ``-i <path>`` option. You can also use multiple inventory files at the same time as described in :ref:`using_multiple_inventory_sources`, and/or pull inventory from dynamic or cloud sources or different formats (YAML, ini, and so on), as described in :ref:`intro_dynamic_inventory`.
There are two default groups: ``all`` and ``ungrouped``. The ``all`` group contains every host.
The ``ungrouped`` group contains all hosts that don't have another group aside from ``all``.
Every host will always belong to at least 2 groups (``all`` and ``ungrouped`` or ``all`` and some other group). Though ``all`` and ``ungrouped`` are always present, they can be implicit and not appear in group listings like ``group_names``.
You can (and probably will) put each host in more than one group. For example a production webserver in a datacenter in Atlanta might be included in groups called [prod] and [atlanta] and [webservers]. You can create groups that track:
You can store variable values that relate to a specific host or group in inventory. To start with, you may add variables directly to the hosts and groups in your main inventory file. As you add more and more managed nodes to your Ansible inventory, however, you will likely want to store variables in separate host and group variable files. See :ref:`define_variables_in_inventory` for details.
Unique values like non-standard SSH ports work well as host variables. You can add them to your Ansible inventory by adding the port number after the hostname with a colon:
..code-block:: text
badwolf.example.com:5309
Connection variables also work well as host variables:
..note:: If you list non-standard SSH ports in your SSH config file, the ``openssh`` connection will find and use them, but the ``paramiko`` connection will not.
In the above example, running Ansible against the host alias "jumper" will connect to 192.0.2.50 on port 5555. See :ref:`behavioral inventory parameters <behavioral_parameters>` to further customize the connection to hosts.
Values passed in the INI format using the ``key=value`` syntax are interpreted differently depending on where they are declared:
* When declared inline with the host, INI values are interpreted as Python literal structures (strings, numbers, tuples, lists, dicts, booleans, None). Host lines accept multiple ``key=value`` parameters per line. Therefore they need a way to indicate that a space is part of a value rather than a separator.
* When declared in a ``:vars`` section, INI values are interpreted as strings. For example ``var=FALSE`` would create a string equal to 'FALSE'. Unlike host lines, ``:vars`` sections accept only a single entry per line, so everything after the ``=`` must be the value for the entry.
* If a variable value set in an INI inventory must be a certain type (for example, a string or a boolean value), always specify the type with a filter in your task. Do not rely on types set in INI inventories when consuming variables.
* Consider using YAML format for inventory sources to avoid confusion on the actual type of a variable. The YAML inventory plugin processes variable values consistently and correctly.
Generally speaking, this is not the best way to define variables that describe your system policy. Setting variables in the main inventory file is only a shorthand. See :ref:`splitting_out_vars` for guidelines on storing variable values in individual files in the 'host_vars' directory.
Group variables are a convenient way to apply variables to multiple hosts at once. Before executing, however, Ansible always flattens variables, including inventory variables, to the host level. If a host is a member of multiple groups, Ansible reads variable values from all of those groups. If you assign different values to the same variable in different groups, Ansible chooses which value to use based on internal :ref:`rules for merging <how_we_merge>`.
If you need to store lists or hash data, or prefer to keep host and group specific variables separate from the inventory file, see :ref:`splitting_out_vars`.
Although you can store variables in the main inventory file, storing separate host and group variables files may help you organize your variable values more easily. Host and group variable files must use YAML syntax. Valid file extensions include '.yml', '.yaml', '.json', or no file extension.
Ansible loads host and group variable files by searching paths relative to the inventory file or the playbook file. If your inventory file at ``/etc/ansible/hosts`` contains a host named 'foosball' that belongs to two groups, 'raleigh' and 'webservers', that host will use variables in YAML files at the following locations:
For example, if you group hosts in your inventory by datacenter, and each datacenter uses its own NTP server and database server, you can create a file called ``/etc/ansible/group_vars/raleigh`` to store the variables for the ``raleigh`` group:
You can also create *directories* named after your groups or hosts. Ansible will read all the files in these directories in lexicographical order. An example with the 'raleigh' group:
For ``ansible-playbook`` you can also add ``group_vars/`` and ``host_vars/`` directories to your playbook directory. Other Ansible commands (for example, ``ansible``, ``ansible-console``, and so on) will only look for ``group_vars/`` and ``host_vars/`` in the inventory directory. If you want other commands to load group and host variables from a playbook directory, you must provide the ``--playbook-dir`` option on the command line.
If you load inventory files from both the playbook directory and the inventory directory, variables in the playbook directory will override variables set in the inventory directory.
By default variables are merged/flattened to the specific host before a play is run. This keeps Ansible focused on the Host and Task, so groups don't really survive outside of inventory and host matching. By default, Ansible overwrites variables including the ones defined for a group and/or host (see :ref:`DEFAULT_HASH_BEHAVIOUR<DEFAULT_HASH_BEHAVIOUR>`). The order/precedence is (from lowest to highest):
By default Ansible merges groups at the same parent/child level in ASCII order, and the last group loaded overwrites the previous groups. For example, an a_group will be merged with b_group and b_group vars that match will overwrite the ones in a_group.
You can change this behavior by setting the group variable ``ansible_group_priority`` to change the merge order for groups of the same level (after the parent/child order is resolved). The larger the number, the later it will be merged, giving it higher priority. This variable defaults to ``1`` if not set. For example:
In this example, if both groups have the same priority, the result would normally have been ``testvar == b``, but since we are giving the ``a_group`` a higher priority the result will be ``testvar == a``.
..note::``ansible_group_priority`` can only be set in the inventory source and not in group_vars/, as the variable is used in the loading of group_vars.
Connection type to the host. This can be the name of any of ansible's connection plugins. SSH protocol types are ``smart``, ``ssh`` or ``paramiko``. The default is smart. Non-SSH based types are described in the next section.
Equivalent to ``ansible_sudo_password`` or ``ansible_su_password``, allows you to set the privilege escalation password (never store this variable in plain text; always use a vault. See :ref:`tip_for_variables_and_vaults`)
Equivalent to ``ansible_sudo_exe`` or ``ansible_su_exe``, allows you to set the executable for the escalation method selected
ansible_become_flags
Equivalent to ``ansible_sudo_flags`` or ``ansible_su_flags``, allows you to set the flags passed to the selected escalation method. This can be also set globally in :file:`ansible.cfg` in the ``sudo_flags`` option
This connector deploys the playbook directly into Docker containers using the local Docker client. The following parameters are processed by this connector:
The user name to operate within the container. The user must exist inside the container.
ansible_become
If set to ``true`` the ``become_user`` will be used to operate within the container.
ansible_docker_extra_args
Could be a string with any additional arguments understood by Docker, which are not command specific. This parameter is mainly used to configure a remote Docker daemon to use.
..note:: If you're reading the docs from the beginning, this may be the first example you've seen of an Ansible playbook. This is not an inventory file.
Playbooks will be covered in great detail later in the docs.