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Versioning docs and examples for v1.4.0-alpha.0.

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David McMahon
2016-06-10 14:21:20 -07:00
parent 09a35325de
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docs/devel/scheduler.md
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
width="25" height="25">
<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
If you are using a released version of Kubernetes, you should
refer to the docs that go with that version.
<!-- TAG RELEASE_LINK, added by the munger automatically -->
<strong>
The latest release of this document can be found
[here](http://releases.k8s.io/release-1.2/docs/devel/scheduler.md).
Documentation for other releases can be found at
[releases.k8s.io](http://releases.k8s.io).
</strong>
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@@ -54,30 +25,37 @@ divided by the node's capacity).
Finally, the node with the highest priority is chosen
(or, if there are multiple such nodes, then one of them is chosen at random). The code
for this main scheduling loop is in the function `Schedule()` in
[plugin/pkg/scheduler/generic_scheduler.go](http://releases.k8s.io/HEAD/plugin/pkg/scheduler/generic_scheduler.go)
[plugin/pkg/scheduler/generic_scheduler.go](http://releases.k8s.io/v1.4.0-alpha.0/plugin/pkg/scheduler/generic_scheduler.go)
## Scheduler extensibility
The scheduler is extensible: the cluster administrator can choose which of the pre-defined
scheduling policies to apply, and can add new ones. The built-in predicates and priorities are
defined in [plugin/pkg/scheduler/algorithm/predicates/predicates.go](http://releases.k8s.io/HEAD/plugin/pkg/scheduler/algorithm/predicates/predicates.go) and
[plugin/pkg/scheduler/algorithm/priorities/priorities.go](http://releases.k8s.io/HEAD/plugin/pkg/scheduler/algorithm/priorities/priorities.go), respectively.
defined in [plugin/pkg/scheduler/algorithm/predicates/predicates.go](http://releases.k8s.io/v1.4.0-alpha.0/plugin/pkg/scheduler/algorithm/predicates/predicates.go) and
[plugin/pkg/scheduler/algorithm/priorities/priorities.go](http://releases.k8s.io/v1.4.0-alpha.0/plugin/pkg/scheduler/algorithm/priorities/priorities.go), respectively.
The policies that are applied when scheduling can be chosen in one of two ways. Normally,
the policies used are selected by the functions `defaultPredicates()` and `defaultPriorities()` in
[plugin/pkg/scheduler/algorithmprovider/defaults/defaults.go](http://releases.k8s.io/HEAD/plugin/pkg/scheduler/algorithmprovider/defaults/defaults.go).
[plugin/pkg/scheduler/algorithmprovider/defaults/defaults.go](http://releases.k8s.io/v1.4.0-alpha.0/plugin/pkg/scheduler/algorithmprovider/defaults/defaults.go).
However, the choice of policies
can be overridden by passing the command-line flag `--policy-config-file` to the scheduler, pointing to a JSON
file specifying which scheduling policies to use. See
[examples/scheduler-policy-config.json](../../examples/scheduler-policy-config.json) for an example
config file. (Note that the config file format is versioned; the API is defined in
[plugin/pkg/scheduler/api](http://releases.k8s.io/HEAD/plugin/pkg/scheduler/api/)).
[plugin/pkg/scheduler/api](http://releases.k8s.io/v1.4.0-alpha.0/plugin/pkg/scheduler/api/)).
Thus to add a new scheduling policy, you should modify predicates.go or priorities.go,
and either register the policy in `defaultPredicates()` or `defaultPriorities()`, or use a policy config file.
## Exploring the code
If you want to get a global picture of how the scheduler works, you can start in
[plugin/cmd/kube-scheduler/app/server.go](http://releases.k8s.io/HEAD/plugin/cmd/kube-scheduler/app/server.go)
[plugin/cmd/kube-scheduler/app/server.go](http://releases.k8s.io/v1.4.0-alpha.0/plugin/cmd/kube-scheduler/app/server.go)
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