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142 lines
5.7 KiB
Markdown
142 lines
5.7 KiB
Markdown
# AWX
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AWX provides a web interface and distributed task engine for scheduling and
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running Ansible playbooks. As such, it relies heavily on the interfaces
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provided by Ansible. This document provides a birds-eye view of the notable
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touchpoints between AWX and Ansible.
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## Terminology
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AWX has a variety of concepts which map to components of Ansible, or
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which further abstract them to provide functionality on top of Ansible. A few
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of the most notable ones are:
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### Projects
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Projects represent a collection of Ansible playbooks. Most AWX users create
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Projects that import periodically from source control systems (such as git,
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mercurial, or subversion repositories). This import is accomplished via an
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Ansible playbook included with AWX (which makes use of the various source
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control management modules in Ansible).
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### Inventories
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AWX manages Inventories, Groups, and Hosts, and provides a RESTful interface
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that maps to static and dynamic Ansible inventories. Inventory data can
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be entered into AWX manually, but many users perform Inventory Syncs to import
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inventory data from a variety of external sources.
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### Job Templates
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A Job Template is a definition and set of parameters for running
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`ansible-playbook`. If defines metadata about a given playbook run, such as:
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* a named identifier
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* an associated inventory to run against
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* the project and `.yml` playbook to run
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* a variety of other options which map directly to `ansible-playbook`
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arguments (`extra_vars`, verbosity, forks, limit, etc...)
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### Credentials
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AWX stores sensitive credential data which can be attached to `ansible-playbook`
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processes that it runs. This data can be oriented towards SSH connection
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authentication (usernames, passwords, SSH keys and passphrases),
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Ansible-specific prompts (such as Vault passwords), or environmental
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authentication values which various Ansible modules depend on (such as setting
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`AWS_ACCESS_KEY_ID` in an environment variable, or specifying
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`ansible_ssh_user` as an extra variable).
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## Canonical Example
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Bringing all of this terminology together, a "Getting Started Using AWX" might
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involve:
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* Creating a new Project that imports playbooks from, for example, a remote git repository
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* Manually creating or importing an Inventory which defines where the playbook(s) will run
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* Optionally, saving a Credential which contains SSH authentication details for
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the host(s) where the playbook will run
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* Creating a Job Template that specifies which Project and playbook to run and
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where to run it (Inventory), and any necessary Credentials (*e.g.*, SSH
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authentication)
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* Launching the Job Template and viewing the results
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## AWX's Interaction with Ansible
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The touchpoints between AWX and Ansible are mostly encompassed by
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everything that happens *after* a job is started in AWX. Specifically, this
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includes:
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* Any time a Job Template is launched
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* Any time a Project Update is performed
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* Any time an Inventory Sync is performed
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* Any time an Adhoc Command is run
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### Spawning Ansible Processes
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AWX relies on a handful of stable interfaces in its interaction with Ansible.
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The first of these are the actual CLI for `ansible-playbook` and
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`ansible-inventory`.
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When a Job Template or Project Update is run in AWX, an actual
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`ansible-playbook` command is composed and spawned in a pseudoterminal on one
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of the servers/containers that make up the AWX installation. This process runs
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until completion (or until a configurable timeout), and the return code,
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`stdout`, and `stderr` of the process are recorded in the AWX database. Ad hoc
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commands work the same way, though they spawn `ansible` processes instead of
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`ansible-playbook`.
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Similarly, when an Inventory Sync runs, an actual `ansible-inventory` process
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runs, and its output is parsed and persisted into the AWX database as Hosts and
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Groups.
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AWX relies on stability in CLI behavior to function properly across Ansible
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releases; this includes the actual CLI arguments _and_ the behavior of task
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execution and prompts (such as password, `become`, and Vault prompts).
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### Capturing Event Data
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AWX applies an Ansible callback plugin to all `ansible-playbook` and `ansible`
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processes it spawns. This allows Ansible events to be captured and persisted
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into the AWX database; this process is what drives the "streaming" web UI
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you'll see if you launch a job from the AWX web interface and watch its results
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appears on the screen. AWX relies on stability in this plugin interface, the
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heirarchy of emitted events based on strategy, and _especially_ the structure
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of event data to work across Ansible releases:
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### Fact Caching
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AWX provides a custom fact caching implementation that allows users to store
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facts for playbook runs across subsequent Job Template runs. Specifically, AWX
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makes use of the `jsonfile` fact cache plugin; after `ansible-playbook` runs
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have exited, AWX consumes the entire `jsonfile` cache and persists it in the
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AWX database. On subsequent Job Template runs, prior `jsonfile` caches are
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restored to the local file system so the new `ansible-playbook` process makes
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use of them.
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### Environment-Based Configuration
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AWX injects credentials and module configuration for a number of Ansible
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modules via environment variables. Examples include:
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* `ANSIBLE_NET_*` and other well-known environment variables for network device authentication
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* API keys and other credential values which are utilized
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(`AWS_ACCESS_KEY_ID`, `GCE_EMAIL`, etc...)
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* SSH-oriented configuration flags, such as `ANSIBLE_SSH_CONTROL_PATH`
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AWX relies on stability in these configuration options to reliably support
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credential injection for supported Ansible modules.
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