15. Glossary¶

Ad Hoc: Refers to running Ansible to perform some quick command, using /usr/bin/ansible, rather than the orchestration language, which is /usr/bin/ansible-playbook. An example of an ad-hoc command might be rebooting 50 machines in your infrastructure. Anything you can do ad-hoc can be accomplished by writing a playbook, and playbooks can also glue lots of other operations together.
Credentials: Authentication details that may be utilized by Tower to launch jobs against machines, to synchronize with inventory sources, and to import project content from a version control system.
Facts: Facts are simply things that are discovered about remote nodes. While they can be used in playbooks and templates just like variables, facts are things that are inferred, rather than set. Facts are automatically discovered when running plays by executing the internal setup module on the remote nodes. You never have to call the setup module explicitly, it just runs, but it can be disabled to save time if it is not needed. For the convenience of users who are switching from other configuration management systems, the fact module also pulls in facts from the ‘ohai’ and ‘facter’ tools if they are installed, which are fact libraries from Chef and Puppet, respectively.
Forks: Ansible and Tower talk to remote nodes in parallel and the level of parallelism can be set serveral ways–during the creation or editing of a Job Template, by passing --forks, or by editing the default in a configuration file. The default is a very conservative 5 forks, though if you have a lot of RAM, you can easily set this to a value like 50 for increased parallelism.
Group: A set of hosts in Ansible that can be addressed as a set, of which many may exist within a single Inventory.
Host: A system managed by Tower, which may include a physical, virtual, cloud-based server, or other device. Typically an operating system instance. Hosts are contained in Inventory. Sometimes referred to as a “node”.
Host Specifier: Each Play in Ansible maps a series of tasks (which define the role, purpose, or orders of a system) to a set of systems. This “hosts:” directive in each play is often called the hosts specifier. It may select one system, many systems, one or more groups, or even some hosts that are in one group and explicitly not in another.
Inventory: A collection of hosts against which Jobs may be launched.
Inventory Script: A very simple program (or a complicated one) that looks up hosts, group membership for hosts, and variable information from an external resource–whether that be a SQL database, a CMDB solution, or something like LDAP. This concept was adapted from Puppet (where it is called an “External Nodes Classifier”) and works more or less exactly the same way.
Inventory Source: Information about a cloud or other script that should be merged into the current inventory group, resulting in the automatic population of Groups, Hosts, and variables about those groups and hosts.
Job: One of many background tasks launched by Tower, this is usually the instantiation of a Job Template; the launch of an Ansible playbook. Other types of jobs include inventory imports, project synchronizations from source control, or administrative cleanup actions.
Job Detail: The history of running a particular job, including its output and success/failure status.
Job Template: The combination of an Ansible playbook and the set of parameters required to launch it.
JSON: Ansible and Tower use JSON for return data from remote modules. This allows modules to be written in any language, not just Python.
Organization: A logical collection of Users, Teams, Projects, and Inventories. The highest level in the Tower object hierarchy is the Organization.
Organization Administrator: An Tower user with the rights to modify the Organization’s membership and settings, including making new users and projects within that organization. An organization admin can also grant permissions to other users within the organization.
Permissions: The set of privileges assigned to Users and Teams that provide the ability to read, modify, and administer Projects, Inventories, and other Tower objects.
Plays: A playbook is a list of plays. A play is minimally a mapping between a set of hosts selected by a host specifier (usually chosen by groups, but sometimes by hostname globs) and the tasks which run on those hosts to define the role that those systems will perform. There can be one or many plays in a playbook.
Playbook: An Ansible playbook. Refer to http://docs.ansible.com/ for more information.
Project: A logical collection of Ansible playbooks, represented in Tower.
Roles: Roles are units of organization in Ansible and Tower. Assigning a role to a group of hosts (or a set of groups, or host patterns, etc.) implies that they should implement a specific behavior. A role may include applying certain variable values, certain tasks, and certain handlers–or just one or more of these things. Because of the file structure associated with a role, roles become redistributable units that allow you to share behavior among playbooks–or even with other users.
Schedule: The calendar of dates and times for which a job should run automatically.
Sudo: Ansible does not require root logins and, since it is daemonless, does not require root level daemons (which can be a security concern in sensitive environments). Ansible can log in and perform many operations wrapped in a sudo command, and can work with both password-less and password-based sudo. Some operations that do not normally work with sudo (like scp file transfer) can be achieved with Ansible’s copy, template, and fetch modules while running in sudo mode.
Superuser: An admin of the Tower server who has permission to edit any object in the system, whether associated to any organization. Superusers can create organizations and other superusers.
Survey: Questions asked by a job template at job launch time, configurable on the job template.
Team: A sub-division of an Organization with associated Users, Projects, Credentials, and Permissions. Teams provide a means to implement role-based access control schemes and delegate responsibilities across Organizations.
User: An Tower operator with associated permissions and credentials.
YAML: Ansible and Tower use YAML to define playbook configuration languages and also variable files. YAML has a minimum of syntax, is very clean, and is easy for people to skim. It is a good data format for configuration files and humans, but is also machine readable. YAML is fairly popular in the dynamic language community and the format has libraries available for serialization in many languages (Python, Perl, Ruby, etc.).