83 lines
4.1 KiB
Plaintext
83 lines
4.1 KiB
Plaintext
---
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layout: docs
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page_title: Device Plugins
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sidebar_title: Devices
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description: Learn how to author a Nomad device plugin.
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---
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# Devices
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Nomad has built-in support for scheduling compute resources such as CPU, memory,
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and networking. Nomad device plugins are used to support scheduling tasks with
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other devices, such as GPUs. They are responsible for fingerprinting these
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devices and working with the Nomad client to make them available to assigned
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tasks.
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For a real world example of a Nomad device plugin implementation, see the [Nvidia
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GPU plugin](https://github.com/hashicorp/nomad/tree/master/devices/gpu/nvidia).
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## Authoring Device Plugins
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Authoring a device plugin in Nomad consists of implementing the
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[DevicePlugin][deviceplugin] interface alongside
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a main package to launch the plugin.
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The [device plugin skeleton project][skeletonproject] exists to help bootstrap
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the development of new device plugins. It provides most of the boilerplate
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necessary for a device plugin, along with detailed comments.
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### Lifecycle and State
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A device plugin is long-lived. Nomad will ensure that one instance of the plugin is
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running. If the plugin crashes or otherwise terminates, Nomad will launch another
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instance of it.
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However, unlike [task drivers](/docs/internals/plugins/task-drivers), device plugins do not currently
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have an interface for persisting state to the Nomad client. Instead, the device
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plugin API emphasizes fingerprinting devices and reporting their status. After
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helping to provision a task with a scheduled device, a device plugin does not
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have any responsibility (or ability) to monitor the task.
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## Device Plugin API
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The [base plugin][baseplugin] must be implemented in addition to the following
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functions.
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### `Fingerprint(context.Context) (<-chan *FingerprintResponse, error)`
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The `Fingerprint` [function][fingerprintfn] is called by the client when the plugin is started.
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It allows the plugin to provide Nomad with a list of discovered devices, along with their
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attributes, for the purpose of scheduling workloads using devices.
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The channel returned should immediately send an initial
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[`FingerprintResponse`][fingerprintresponse], then send periodic updates at
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an appropriate interval until the context is canceled.
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Each fingerprint response consists of either an error or a list of device groups.
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A device group is a list of detected devices that are identical for the purpose of
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scheduling; that is, they will have identical attributes.
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### `Stats(context.Context, time.Duration) (<-chan *StatsResponse, error)`
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The `Stats` [function][statsfn] returns a channel on which the plugin should
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emit device statistics, at the specified interval, until either an error is
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encountered or the specified context is cancelled. The `StatsReponse` object
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allows [dimensioned][dimensioned] statistics to be returned for each device in a device group.
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### `Reserve(deviceIDs []string) (*ContainerReservation, error)`
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The `Reserve` [function][reservefn] accepts a list of device IDs and returns the information
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necessary for the client to make those devices available to a task. Currently,
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the `ContainerReservation` object allows the plugin to specify environment
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variables for the task, as well as a list of host devices and files to be mounted
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into the task's filesystem. Any orchestration required to prepare the device for
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use should also be performed in this function.
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[deviceplugin]: https://github.com/hashicorp/nomad/blob/v0.9.0/plugins/device/device.go#L20-L33
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[baseplugin]: /docs/internals/plugins/base
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[skeletonproject]: https://github.com/hashicorp/nomad-skeleton-device-plugin
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[fingerprintresponse]: https://github.com/hashicorp/nomad/blob/v0.9.0/plugins/device/device.go#L37-L43
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[fingerprintfn]: https://github.com/hashicorp/nomad-skeleton-device-plugin/blob/v0.1.0/device/device.go#L159-L165
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[statsfn]: https://github.com/hashicorp/nomad-skeleton-device-plugin/blob/v0.1.0/device/device.go#L169-L176
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[reservefn]: https://github.com/hashicorp/nomad-skeleton-device-plugin/blob/v0.1.0/device/device.go#L189-L245
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[dimensioned]: https://github.com/hashicorp/nomad/blob/v0.9.0/plugins/shared/structs/stats.go#L33-L34
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