Working with Inventory ¶

Topics

Working with Inventory

Ansible works against multiple systems in your infrastructure at the same time. It does this by selecting portions of systems listed in Ansible’s inventory, which defaults to being saved in the location /etc/ansible/hosts. You can specify a different inventory file using the -i <path> option on the command line.

Not only is this inventory configurable, but you can also use multiple inventory files at the same time and pull inventory from dynamic or cloud sources or different formats (YAML, ini, etc), as described in Working With Dynamic Inventory. Introduced in version 2.4, Ansible has inventory plugins to make this flexible and customizable.

Hosts and Groups ¶

The inventory file can be in one of many formats, depending on the inventory plugins you have. For this example, the format for /etc/ansible/hosts is an INI-like (one of Ansible’s defaults) and looks like this:

mail.example.com

[webservers]
foo.example.com
bar.example.com

[dbservers]
one.example.com
two.example.com
three.example.com

The headings in brackets are group names, which are used in classifying systems and deciding what systems you are controlling at what times and for what purpose.

A YAML version would look like:

all:
  hosts:
    mail.example.com:
  children:
    webservers:
      hosts:
        foo.example.com:
        bar.example.com:
    dbservers:
      hosts:
        one.example.com:
        two.example.com:
        three.example.com:

It is ok to put systems in more than one group, for instance a server could be both a webserver and a dbserver. If you do, note that variables will come from all of the groups they are a member of. Variable precedence is detailed in a later chapter.

If you have hosts that run on non-standard SSH ports you can put the port number after the hostname with a colon. Ports listed in your SSH config file won’t be used with the paramiko connection but will be used with the openssh connection.

To make things explicit, it is suggested that you set them if things are not running on the default port:

badwolf.example.com:5309

Suppose you have just static IPs and want to set up some aliases that live in your host file, or you are connecting through tunnels. You can also describe hosts via variables:

In INI:

jumper ansible_port=5555 ansible_host=192.0.2.50

In YAML:

...
  hosts:
    jumper:
      ansible_port: 5555
      ansible_host: 192.0.2.50

In the above example, trying to ansible against the host alias “jumper” (which may not even be a real hostname) will contact 192.0.2.50 on port 5555. Note that this is using a feature of the inventory file to define some special variables. Generally speaking, this is not the best way to define variables that describe your system policy, but we’ll share suggestions on doing this later.

Note

Values passed in the INI format using the key=value syntax are not interpreted as Python literal structure (strings, numbers, tuples, lists, dicts, booleans, None), but as a string. For example var=FALSE would create a string equal to ‘FALSE’. Do not rely on types set during definition, always make sure you specify type with a filter when needed when consuming the variable.

If you are adding a lot of hosts following similar patterns, you can do this rather than listing each hostname:

[webservers]
www[01:50].example.com

For numeric patterns, leading zeros can be included or removed, as desired. Ranges are inclusive. You can also define alphabetic ranges:

[databases]
db-[a:f].example.com

You can also select the connection type and user on a per host basis:

[targets]

localhost              ansible_connection=local
other1.example.com     ansible_connection=ssh        ansible_user=mpdehaan
other2.example.com     ansible_connection=ssh        ansible_user=mdehaan

As mentioned above, setting these in the inventory file is only a shorthand, and we’ll discuss how to store them in individual files in the ‘host_vars’ directory a bit later on.

Host Variables ¶

As described above, it is easy to assign variables to hosts that will be used later in playbooks:

[atlanta]
host1 http_port=80 maxRequestsPerChild=808
host2 http_port=303 maxRequestsPerChild=909

Group Variables ¶

Variables can also be applied to an entire group at once:

The INI way:

[atlanta]
host1
host2

[atlanta:vars]
ntp_server=ntp.atlanta.example.com
proxy=proxy.atlanta.example.com

The YAML version:

atlanta:
  hosts:
    host1:
    host2:
  vars:
    ntp_server: ntp.atlanta.example.com
    proxy: proxy.atlanta.example.com

Be aware that this is only a convenient way to apply variables to multiple hosts at once; even though you can target hosts by group, variables are always flattened to the host level before a play is executed.

Groups of Groups, and Group Variables ¶

It is also possible to make groups of groups using the :children suffix in INI or the children: entry in YAML. You can apply variables using :vars or vars::

[atlanta]
host1
host2

[raleigh]
host2
host3

[southeast:children]
atlanta
raleigh

[southeast:vars]
some_server=foo.southeast.example.com
halon_system_timeout=30
self_destruct_countdown=60
escape_pods=2

[usa:children]
southeast
northeast
southwest
northwest

all:
  children:
    usa:
      children:
        southeast:
          children:
            atlanta:
              hosts:
                host1:
                host2:
            raleigh:
              hosts:
                host2:
                host3:
          vars:
            some_server: foo.southeast.example.com
            halon_system_timeout: 30
            self_destruct_countdown: 60
            escape_pods: 2
        northeast:
        northwest:
        southwest:

If you need to store lists or hash data, or prefer to keep host and group specific variables separate from the inventory file, see the next section. Child groups have a couple of properties to note:

Any host that is member of a child group is automatically a member of the parent group.

A child group’s variables will have higher precedence (override) a parent group’s variables.

Groups can have multiple parents and children, but not circular relationships.

Hosts can also be in multiple groups, but there will only be one instance of a host, merging the data from the multiple groups.

Default groups ¶

There are two default groups: all and ungrouped. all contains every host. ungrouped contains all hosts that don’t have another group aside from all. Every host will always belong to at least 2 groups. Though all and ungrouped are always present, they can be implicit and not appear in group listings like group_names.

Splitting Out Host and Group Specific Data ¶

The preferred practice in Ansible is to not store variables in the main inventory file.

In addition to storing variables directly in the inventory file, host and group variables can be stored in individual files relative to the inventory file (not directory, it is always the file).

These variable files are in YAML format. Valid file extensions include ‘.yml’, ‘.yaml’, ‘.json’, or no file extension. See YAML Syntax if you are new to YAML.

Assuming the inventory file path is:

/etc/ansible/hosts

If the host is named ‘foosball’, and in groups ‘raleigh’ and ‘webservers’, variables in YAML files at the following locations will be made available to the host:

/etc/ansible/group_vars/raleigh # can optionally end in '.yml', '.yaml', or '.json'
/etc/ansible/group_vars/webservers
/etc/ansible/host_vars/foosball

For instance, suppose you have hosts grouped by datacenter, and each datacenter uses some different servers. The data in the groupfile ‘/etc/ansible/group_vars/raleigh’ for the ‘raleigh’ group might look like:

---
ntp_server: acme.example.org
database_server: storage.example.org

It is okay if these files do not exist, as this is an optional feature.

As an advanced use case, you can create directories named after your groups or hosts, and Ansible will read all the files in these directories in lexicographical order. An example with the ‘raleigh’ group:

/etc/ansible/group_vars/raleigh/db_settings
/etc/ansible/group_vars/raleigh/cluster_settings

All hosts that are in the ‘raleigh’ group will have the variables defined in these files available to them. This can be very useful to keep your variables organized when a single file starts to be too big, or when you want to use Ansible Vault on a part of a group’s variables.

Tip: The group_vars/ and host_vars/ directories can exist in the playbook directory OR the inventory directory. If both paths exist, variables in the playbook directory will override variables set in the inventory directory.

Tip: Keeping your inventory file and variables in a git repo (or other version control) is an excellent way to track changes to your inventory and host variables.

How Variables Are Merged ¶

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 the hash_merge setting to change this) . The order/precedence is (from lowest to highest):

all group (because it is the ‘parent’ of all other groups)
parent group
child group
host

When groups of the same parent/child level are merged, it is done alphabetically, 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.

New in version 2.4.

Starting in Ansible version 2.4, users can use 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:

a_group:
    testvar: a
    ansible_group_priority: 10
b_group：
    testvar: b

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.

List of Behavioral Inventory Parameters ¶

As described above, setting the following variables control how Ansible interacts with remote hosts.

Host connection:

Note

Ansible does not expose a channel to allow communication between the user and the ssh process to accept a password manually to decrypt an ssh key when using the ssh connection plugin (which is the default). The use of ssh-agent is highly recommended.

ansible_connection: 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.

General for all connections:

ansible_host: The name of the host to connect to, if different from the alias you wish to give to it.
ansible_port: The ssh port number, if not 22
ansible_user: The default ssh user name to use.

Specific to the SSH connection:

ansible_ssh_pass: The ssh password to use (never store this variable in plain text; always use a vault. See Variables and Vaults)
ansible_ssh_private_key_file: Private key file used by ssh. Useful if using multiple keys and you don’t want to use SSH agent.
ansible_ssh_common_args: This setting is always appended to the default command line for sftp, scp, and ssh. Useful to configure a ProxyCommand for a certain host (or group).
ansible_sftp_extra_args: This setting is always appended to the default sftp command line.
ansible_scp_extra_args: This setting is always appended to the default scp command line.
ansible_ssh_extra_args: This setting is always appended to the default ssh command line.
ansible_ssh_pipelining: Determines whether or not to use SSH pipelining. This can override the pipelining setting in ansible.cfg.
ansible_ssh_executable (added in version 2.2): This setting overrides the default behavior to use the system ssh. This can override the ssh_executable setting in ansible.cfg.

Privilege escalation (see Ansible Privilege Escalation for further details):

ansible_become: Equivalent to ansible_sudo or ansible_su, allows to force privilege escalation
ansible_become_method: Allows to set privilege escalation method
ansible_become_user: Equivalent to ansible_sudo_user or ansible_su_user, allows to set the user you become through privilege escalation
ansible_become_pass: Equivalent to ansible_sudo_pass or ansible_su_pass, allows you to set the privilege escalation password (never store this variable in plain text; always use a vault. See Variables and Vaults)
ansible_become_exe: 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 ansible.cfg in the sudo_flags option

Remote host environment parameters:

ansible_shell_type: The shell type of the target system. You should not use this setting unless you have set the ansible_shell_executable to a non-Bourne (sh) compatible shell. By default commands are formatted using sh-style syntax. Setting this to csh or fish will cause commands executed on target systems to follow those shell’s syntax instead.

ansible_python_interpreter: The target host python path. This is useful for systems with more than one Python or not located at /usr/bin/python such as *BSD, or where /usr/bin/python is not a 2.X series Python. We do not use the /usr/bin/env mechanism as that requires the remote user’s path to be set right and also assumes the python executable is named python, where the executable might be named something like python2.6.
ansible_*_interpreter: Works for anything such as ruby or perl and works just like ansible_python_interpreter. This replaces shebang of modules which will run on that host.

New in version 2.1.

ansible_shell_executable: This sets the shell the ansible controller will use on the target machine, overrides executable in ansible.cfg which defaults to /bin/sh. You should really only change it if is not possible to use /bin/sh (i.e. /bin/sh is not installed on the target machine or cannot be run from sudo.).

Examples from an Ansible-INI host file:

some_host         ansible_port=2222     ansible_user=manager
aws_host          ansible_ssh_private_key_file=/home/example/.ssh/aws.pem
freebsd_host      ansible_python_interpreter=/usr/local/bin/python
ruby_module_host  ansible_ruby_interpreter=/usr/bin/ruby.1.9.3

Non-SSH connection types ¶

As stated in the previous section, Ansible executes playbooks over SSH but it is not limited to this connection type. With the host specific parameter ansible_connection=<connector>, the connection type can be changed. The following non-SSH based connectors are available:

local

This connector can be used to deploy the playbook to the control machine itself.

docker

This connector deploys the playbook directly into Docker containers using the local Docker client. The following parameters are processed by this connector:

ansible_host: The name of the Docker container to connect to.
ansible_user: 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.

Here is an example of how to instantly deploy to created containers:

- name: create jenkins container
  docker_container:
    docker_host: myserver.net:4243
    name: my_jenkins
    image: jenkins

- name: add container to inventory
  add_host:
    name: my_jenkins
    ansible_connection: docker
    ansible_docker_extra_args: "--tlsverify --tlscacert=/path/to/ca.pem --tlscert=/path/to/client-cert.pem --tlskey=/path/to/client-key.pem -H=tcp://myserver.net:4243"
    ansible_user: jenkins
  changed_when: false

- name: create directory for ssh keys
  delegate_to: my_jenkins
  file:
    path: "/var/jenkins_home/.ssh/jupiter"
    state: directory

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.