awx/docs/job_slicing.md

# Job Slicing Overview

Ansible, by default, runs jobs from a single control instance. At best, a single Ansible job can be sliced up on a single system via forks but this doesn't fully take advantage of AWX's ability to distribute work to multiple nodes in a cluster.

Job Slicing solves this problem by adding a Job Template field `job_slice_count`. This field specifies the number of **Jobs** to slice the Ansible run into. When this number is greater than one, `AWX` will generate a **Workflow** from a **Job Template** instead of a **Job**. The **Inventory** will be distributed evenly amongst the sliced jobs. The workflow job is then started and proceeds as though it were a normal workflow.  The API will return either a **Job** resource (if `job_slice_count` < 2) or a **WorkflowJob** resource otherwise. Likewise, the UI will redirect to the appropriate screen to display the status of the run.


## Implications for Job Execution

When jobs are sliced, they can run on any Tower node; however, some may not run at the same time. Because of this, anything that relies on setting/sliced state (using modules such as `set_fact`) will not work as expected. It's reasonable to expect that not all jobs will actually run at the same time (*e.g.*, if there is not enough capacity in the system)


## Simultaneous Execution Behavior

By default, Job Templates aren't normally configured to execute simultaneously (`allow_simultaneous` must be checked). Slicing overrides this behavior and implies `allow_simultaneous`, even if that setting is not selected.