---
title: External Resources
weight: 2
type: docs
aliases:
  - /deployment/advanced/external_resources.html
  - /ops/external_resources.html
---
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# External Resource Framework

In addition to CPU and memory, many workloads also need some other resources, e.g. GPUs for deep learning. To support external
resources, Flink provides an external resource framework. The framework supports requesting various types of resources from the
underlying resource management systems (e.g., Kubernetes), and supplies information needed for using these resources to the operators.
Different resource types can be supported. You can either leverage built-in plugins provided by Flink (currently only for GPU support),
or implement your own plugins for custom resource types.

# What the external resource framework does

In general, the external resource framework does two things:

  - Set the corresponding fields of the resource requests (for requesting resources from the underlying system) with respect to your configuration.

  - Provide operators with the *information* needed for using the resources.

When deployed on resource management systems (Kubernetes / Yarn), the external resource framework will ensure that the allocated pod/container
will contain the desired external resources. Currently, many resource management systems support external resources. For example,
Kubernetes supports GPU, FPGA, etc. through its [Device Plugin](https://kubernetes.io/docs/concepts/extend-kubernetes/compute-storage-net/device-plugins/)
mechanism since v1.10, and Yarn supports GPU and FPGA resources since 2.10 and 3.1. In Standalone mode, the user has to ensure that the external resources are available.

The external resource framework will provide the corresponding *information* to operators. The external resource information,
which contains the basic properties needed for using the resources, is generated by the configured external resource *drivers*.

# Enable the external resource framework for your workload

To enable an external resource with the external resource framework, you need to:

  - Prepare the external resource *plugin*.

  - Set configurations for the external resource.

  - Get the external resource *information* from `RuntimeContext` and use it in your operators.

## Prepare plugins

You need to prepare the external resource plugin and put it into the `plugins/` folder of your Flink distribution, see
[Flink Plugins]({{< ref "docs/deployment/filesystems/plugins" >}}). Apache Flink provides a first-party [plugin for GPU resources](#plugin-for-gpu-resources). You can also
[implement a plugin for your custom resource type](#implement-a-plugin-for-your-custom-resource-type).

## Configurations

First, you need to add resource names for all the external resource types to the **external resource list (with the configuration key ‘external-resources’)**
with delimiter ";", e.g. "external-resources: gpu;fpga" for two external resources "gpu" and "fpga". Only the **\<resource_name\>**
defined here will go into effect in the external resource framework.

For each external resource, you could configure the below options. The **\<resource_name\>** in all the below configuration options
corresponds to the name listed in the **external resource list**:

  - **Amount** (`external.<resource_name>.amount`): This is the quantity of the external resource that should be requested from the external system.

  - **Config key in Yarn** (`external-resource.<resource_name>.yarn.config-key`): *optional*. If configured, the external
  resource framework will add this key to the resource profile of container requests for Yarn. The value will be set to the
  value of `external-resource.<resource_name>.amount`.

  - **Config key in Kubernetes** (`external-resource.<resource_name>.kubernetes.config-key`): *optional*. If configured,
  external resource framework will add `resources.limits.<config-key>` and `resources.requests.<config-key>` to the main
  container spec of TaskManager and set the value to the value of `external-resource.<resource_name>.amount`.

  - **Driver Factory** (`external-resource.<resource_name>.driver-factory.class`): *optional*. Defines the factory class
  name for the external resource identified by **\<resource_name\>**. If configured, the factory will be used to instantiate
  *drivers* in the external resource framework. If not configured, the requested resource will still exist in the `TaskManager`
  as long as the relevant options are configured. However, the operator will not get any information of the resource from `RuntimeContext` in that case.

  - **Driver Parameters** (`external-resource.<resource_name>.param.<param>`): *optional*. The naming pattern of custom
  config options for the external resource specified by **\<resource_name\>**. Only the configurations that follow this pattern
  will be passed into the *driver* factory of that external resource.

An example configuration that specifies two external resources:

```bash
external-resources: gpu;fpga # Define two external resources, "gpu" and "fpga".

external-resource.gpu.driver-factory.class: org.apache.flink.externalresource.gpu.GPUDriverFactory # Define the driver factory class of gpu resource.
external-resource.gpu.amount: 2 # Define the amount of gpu resource per TaskManager.
external-resource.gpu.param.discovery-script.args: --enable-coordination # Define the custom param discovery-script.args which will be passed into the gpu driver.

external-resource.fpga.driver-factory.class: org.apache.flink.externalresource.fpga.FPGADriverFactory # Define the driver factory class of fpga resource.
external-resource.fpga.amount: 1 # Define the amount of fpga resource per TaskManager.
external-resource.fpga.yarn.config-key: yarn.io/fpga # Define the corresponding config key of fpga in Yarn.
```

## Use the resources

To use the resources, operators need to get the `ExternalResourceInfo` set from the `RuntimeContext`. `ExternalResourceInfo`
wraps the information needed for using the resource, which can be retrieved with `getProperty`. What properties are available
and how to access the resource with the properties depends on the specific plugin.

Operators can get the `ExternalResourceInfo` set of a specific external resource from `RuntimeContext` or `FunctionContext` by
`getExternalResourceInfos(String resourceName)`. The `resourceName` here should have the same value as the name configured in the
external resource list. It can be used as follows:

{{< tabs "81f076a6-0048-4fb0-88b8-be8508e969c8" >}}
{{< tab "Java" >}}
```java
public class ExternalResourceMapFunction extends RichMapFunction<String, String> {
    private static final String RESOURCE_NAME = "foo";

    @Override
    public String map(String value) {
        Set<ExternalResourceInfo> externalResourceInfos = getRuntimeContext().getExternalResourceInfos(RESOURCE_NAME);
        List<String> addresses = new ArrayList<>();
        externalResourceInfos.iterator().forEachRemaining(externalResourceInfo ->
            addresses.add(externalResourceInfo.getProperty("address").get()));
        // map function with addresses.
        // ...
    }
}
```
{{< /tab >}}
{{< tab "Scala" >}}
```scala
class ExternalResourceMapFunction extends RichMapFunction[(String, String)] {
    var RESOURCE_NAME = "foo"

    override def map(value: String): String = {
        val externalResourceInfos = getRuntimeContext().getExternalResourceInfos(RESOURCE_NAME)
        val addresses = new util.ArrayList[String]
        externalResourceInfos.asScala.foreach(
        externalResourceInfo => addresses.add(externalResourceInfo.getProperty("address").get()))

        // map function with addresses.
        // ...
    }
}
```
{{< /tab >}}
{{< /tabs >}}

Each `ExternalResourceInfo` contains one or more properties with keys representing the different dimensions of the resource.
You could get all valid keys by `ExternalResourceInfo#getKeys`.

{{< hint info >}}
**Note:** Currently, the information returned by RuntimeContext#getExternalResourceInfos is available to all the operators.
{{< /hint >}}

# Implement a plugin for your custom resource type

To implement a plugin for your custom resource type, you need to:

  - Add your own external resource driver by implementing the `org.apache.flink.api.common.externalresource.ExternalResourceDriver` interface.

  - Add a driver factory, which instantiates the *driver*, by implementing the `org.apache.flink.api.common.externalresource.ExternalResourceDriverFactory`.

  - Add a service entry. Create a file `META-INF/services/org.apache.flink.api.common.externalresource.ExternalResourceDriverFactory`
  which contains the class name of your *driver* factory class (see the [Java Service Loader](https://docs.oracle.com/javase/8/docs/api/java/util/ServiceLoader.html) docs for more details).

For example, to implement a plugin for external resource named "FPGA", you need to implement `FPGADriver` and `FPGADriverFactory` first:

{{< tabs "6d799b04-fa41-42b6-9933-cb1fe288cd81" >}}
{{< tab "Java" >}}
```java
public class FPGADriver implements ExternalResourceDriver {
	@Override
	public Set<FPGAInfo> retrieveResourceInfo(long amount) {
		// return the information set of "FPGA"
	}
}

public class FPGADriverFactory implements ExternalResourceDriverFactory {
	@Override
	public ExternalResourceDriver createExternalResourceDriver(Configuration config) {
		return new FPGADriver();
	}
}

// Also implement FPGAInfo which contains basic properties of "FPGA" resource.
public class FPGAInfo implements ExternalResourceInfo {
	@Override
	public Optional<String> getProperty(String key) {
		// return the property with the given key.
	}

	@Override
	public Collection<String> getKeys() {
		// return all property keys.
	}
}
```
{{< /tab >}}
{{< tab "Scala" >}}
```scala
class FPGADriver extends ExternalResourceDriver {
  override def retrieveResourceInfo(amount: Long): Set[FPGAInfo] = {
    // return the information set of "FPGA"
  }
}

class FPGADriverFactory extends ExternalResourceDriverFactory {
  override def createExternalResourceDriver(config: Configuration): ExternalResourceDriver = {
    new FPGADriver()
  }
}

// Also implement FPGAInfo which contains basic properties of "FPGA" resource.
class FPGAInfo extends ExternalResourceInfo {
  override def getProperty(key: String): Option[String] = {
    // return the property with the given key.
  }

  override def getKeys(): util.Collection[String] = {
    // return all property keys.
  }
}
```
{{< /tab >}}
{{< /tabs >}}

Create a file with name `org.apache.flink.api.common.externalresource.ExternalResourceDriverFactory` in `META-INF/services/`
and write the factory class name (e.g. `your.domain.FPGADriverFactory`) to it.

Then, create a jar which includes `FPGADriver`, `FPGADriverFactory`, `META-INF/services/` and all the external dependencies.
Make a directory in `plugins/` of your Flink distribution with an arbitrary name, e.g. "fpga", and put the jar into this directory.
See [Flink Plugin]({{< ref "docs/deployment/filesystems/plugins" >}}) for more details.

{{< hint info >}}
**Note:** External resources are shared by all operators running on the same machine. The community might add external resource isolation in a future release.
{{< /hint >}}

# Existing supported external resource plugins

Currently, Flink supports GPUs as external resources.

## Plugin for GPU resources

We provide a first-party plugin for GPU resources. The plugin leverages a discovery script to discover indexes of GPU devices, which can
be accessed from the resource *information* via the property "index". We provide a default discovery script that can be used to discover
NVIDIA GPUs. You can also provide your custom script.

We provide {{< gh_link file="/flink-examples/flink-examples-streaming/src/main/java/org/apache/flink/streaming/examples/gpu/MatrixVectorMul.java" name="an example" >}}
which shows how to use the GPUs to do matrix-vector multiplication in Flink.

{{< hint info >}}
**Note:** Currently, for all the operators, RuntimeContext#getExternalResourceInfos returns the same set of resource information. That means, the same set of GPU devices are always accessible to all the operators running in the same TaskManager. There is no operator level isolation at the moment.
{{< /hint >}}

### Pre-requisites

To make GPU resources accessible, certain prerequisites are needed depending on your environment:

  - For standalone mode, administrators should ensure the NVIDIA driver is installed and GPU resources are accessible on all the nodes in the cluster.

  - For Yarn deployment, administrators should configure the Yarn cluster to enable [GPU scheduling](https://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/UsingGpus.html).
  Notice the required Hadoop version is 2.10+ or 3.1+.

  - For Kubernetes deployment, administrators should make sure the NVIDIA GPU [device plugin](https://kubernetes.io/docs/concepts/extend-kubernetes/compute-storage-net/device-plugins/)
  is installed. Notice the required version is 1.10+. At the moment, Kubernetes only supports NVIDIA GPU and AMD GPU. Flink only provides discovery script for NVIDIA GPUs,
  but you can provide a custom discovery script for AMD GPUs yourself, see [Discovery script](#discovery-script).

### Enable GPU resources for your workload

As mentioned in [Enable external resources for your workload](#enable-the-external-resource-framework-for-your-workload),
you also need to do two things to enable GPU resources:

  - Configure the GPU resource.

  - Get the *information* of GPU resources, which contains the GPU index as property with key "index", in operators.

### Configurations

For the GPU plugin, you need to specify the common external resource configurations:

  - `external-resources`: You need to append your resource name (e.g. gpu) for GPU resources to it.

  - `external-resource.<resource_name>.amount`: The amount of GPU devices per TaskManager.

  - `external-resource.<resource_name>.yarn.config-key`: For Yarn, the config key of GPU is `yarn.io/gpu`. Notice that
  Yarn only supports NVIDIA GPU at the moment.

  - `external-resource.<resource_name>.kubernetes.config-key`: For Kubernetes, the config key of GPU is `<vendor>.com/gpu`.
  Currently, "nvidia" and "amd" are the two supported vendors. Notice that if you use AMD GPUs, you need to provide a discovery
  script yourself, see [Discovery script](#discovery-script).

  - external-resource.<resource_name>.driver-factory.class: Should be set to org.apache.flink.externalresource.gpu.GPUDriverFactory.

In addition, there are some specific configurations for the GPU plugin:

  - `external-resource.<resource_name>.param.discovery-script.path`: The path of the [discovery script](#discovery-script). It
  can either be an absolute path, or a relative path to `FLINK_HOME` when defined or current directory otherwise. If not
  explicitly configured, the default script will be used.

  - `external-resource.<resource_name>.param.discovery-script.args`: The arguments passed to the discovery script. For the default
  discovery script, see [Default Script](#default-script) for the available parameters.

An example configuration for GPU resource:

```bash
external-resources: gpu
external-resource.gpu.driver-factory.class: org.apache.flink.externalresource.gpu.GPUDriverFactory # Define the driver factory class of gpu resource.
external-resource.gpu.amount: 2 # Define the amount of gpu resource per TaskManager.
external-resource.gpu.param.discovery-script.path: plugins/external-resource-gpu/nvidia-gpu-discovery.sh
external-resource.gpu.param.discovery-script.args: --enable-coordination # Define the custom param "discovery-script.args" which will be passed into the gpu driver.

external-resource.gpu.yarn.config-key: yarn.io/gpu # for Yarn

external-resource.gpu.kubernetes.config-key: nvidia.com/gpu # for Kubernetes
```

### Discovery script

The `GPUDriver` leverages a discovery script to discover GPU resources and generate the GPU resource information.

#### Default Script

We provide a default discovery script for NVIDIA GPU, located at `plugins/external-resource-gpu/nvidia-gpu-discovery.sh` of your
Flink distribution. The script gets the indexes of visible GPU resources through the `nvidia-smi` command. It tries to return
the required amount (specified by `external-resource.<resource_name>.amount`) of GPU indexes in a list, and exit with non-zero if the amount cannot be satisfied.

For standalone mode, multiple TaskManagers might be co-located on the same machine, and each GPU device is visible to all
the TaskManagers. The default discovery script supports a coordination mode, in which it leverages a coordination file to
synchronize the allocation state of GPU devices and ensure each GPU device can only be used by one TaskManager process. The relevant arguments are:

  - `--enable-coordination-mode`: Enable the coordination mode. By default the coordination mode is disabled.

  - `--coordination-file filePath`: The path of the coordination file used to synchronize the allocation state of GPU resources. The default path is `/var/tmp/flink-gpu-coordination`.

{{< hint info >}}
**Note:** The coordination mode only ensures that a GPU device is not shared by multiple TaskManagers of the same Flink cluster. Please be aware that another Flink cluster (with a different coordination file) or a non-Flink application can still use the same GPU devices.
{{< /hint >}}

#### Custom Script

You can also provide a discovery script to address your custom requirements, e.g. discovering AMD GPU. Please make sure
the path of your custom script is accessible to Flink and configured (`external-resource.<resource_name>.param.discovery-script.path`) correctly.
The contract of the discovery script:

  - `GPUDriver` passes the amount (specified by `external-resource.<resource_name>.amount`) as the first argument into the script.
  The user-defined arguments in `external-resource.<resource_name>.param.discovery-script.args` would be appended after it.

  - The script should return a list of the available GPU indexes, split by a comma. Whitespace only indexes will be ignored.

  - The script can also suggest that the discovery is not properly performed, by exiting with non-zero. In that case, no gpu information will be provided to operators.
