Running Spark on Kubernetes

• Security
  • User Identity
  • Volume Mounts
• Prerequisites
• How it works
• Submitting Applications to Kubernetes
  • Docker Images
  • Cluster Mode
  • Client Mode
    • Client Mode Networking
    • Client Mode Executor Pod Garbage Collection
    • Authentication Parameters
  • Dependency Management
  • Secret Management
  • Pod Template
  • Using Kubernetes Volumes
  • Local Storage
    • Using RAM for local storage
  • Introspection and Debugging
    • Accessing Logs
    • Accessing Driver UI
    • Debugging
  • Kubernetes Features
    • Configuration File
    • Contexts
    • Namespaces
    • RBAC
  • Spark Application Management
  • Future Work
• Configuration
  • Spark Properties
  • Pod template properties
  • Pod Metadata
  • Pod Spec
  • Container spec
  • Resource Allocation and Configuration Overview

Spark can run on clusters managed by Kubernetes. This feature makes use of native Kubernetes scheduler that has been added to Spark.

The Kubernetes scheduler is currently experimental. In future versions, there may be behavioral changes around configuration, container images and entrypoints.

Security

Security in Spark is OFF by default. This could mean you are vulnerable to attack by default. Please see Spark Security and the specific advice below before running Spark.

User Identity

Images built from the project provided Dockerfiles contain a default USER directive with a default UID of 185. This means that the resulting images will be running the Spark processes as this UID inside the container. Security conscious deployments should consider providing custom images with USER directives specifying their desired unprivileged UID and GID. The resulting UID should include the root group in its supplementary groups in order to be able to run the Spark executables. Users building their own images with the provided docker-image-tool.sh script can use the -u <uid> option to specify the desired UID.

Alternatively the Pod Template feature can be used to add a Security Context with a runAsUser to the pods that Spark submits. This can be used to override the USER directives in the images themselves. Please bear in mind that this requires cooperation from your users and as such may not be a suitable solution for shared environments. Cluster administrators should use Pod Security Policies if they wish to limit the users that pods may run as.

Volume Mounts

As described later in this document under Using Kubernetes Volumes Spark on K8S provides configuration options that allow for mounting certain volume types into the driver and executor pods. In particular it allows for hostPath volumes which as described in the Kubernetes documentation have known security vulnerabilities.

Cluster administrators should use Pod Security Policies to limit the ability to mount hostPath volumes appropriately for their environments.

Prerequisites

• A runnable distribution of Spark 2.3 or above.
• A running Kubernetes cluster at version >= 1.6 with access configured to it using kubectl. If you do not already have a working Kubernetes cluster, you may set up a test cluster on your local machine using minikube.
  • We recommend using the latest release of minikube with the DNS addon enabled.
  • Be aware that the default minikube configuration is not enough for running Spark applications. We recommend 3 CPUs and 4g of memory to be able to start a simple Spark application with a single executor.
• You must have appropriate permissions to list, create, edit and delete pods in your cluster. You can verify that you can list these resources by running kubectl auth can-i <list|create|edit|delete> pods.
  • The service account credentials used by the driver pods must be allowed to create pods, services and configmaps.
• You must have Kubernetes DNS configured in your cluster.

How it works

spark-submit can be directly used to submit a Spark application to a Kubernetes cluster. The submission mechanism works as follows:

• Spark creates a Spark driver running within a Kubernetes pod.
• The driver creates executors which are also running within Kubernetes pods and connects to them, and executes application code.
• When the application completes, the executor pods terminate and are cleaned up, but the driver pod persists logs and remains in “completed” state in the Kubernetes API until it’s eventually garbage collected or manually cleaned up.

Note that in the completed state, the driver pod does not use any computational or memory resources.

The driver and executor pod scheduling is handled by Kubernetes. Communication to the Kubernetes API is done via fabric8. It is possible to schedule the driver and executor pods on a subset of available nodes through a node selector using the configuration property for it. It will be possible to use more advanced scheduling hints like node/pod affinities in a future release.

Submitting Applications to Kubernetes

Docker Images

Kubernetes requires users to supply images that can be deployed into containers within pods. The images are built to be run in a container runtime environment that Kubernetes supports. Docker is a container runtime environment that is frequently used with Kubernetes. Spark (starting with version 2.3) ships with a Dockerfile that can be used for this purpose, or customized to match an individual application’s needs. It can be found in the kubernetes/dockerfiles/ directory.

Spark also ships with a bin/docker-image-tool.sh script that can be used to build and publish the Docker images to use with the Kubernetes backend.

Example usage is:

$ ./bin/docker-image-tool.sh -r <repo> -t my-tag build
$ ./bin/docker-image-tool.sh -r <repo> -t my-tag push

This will build using the projects provided default Dockerfiles. To see more options available for customising the behaviour of this tool, including providing custom Dockerfiles, please run with the -h flag.

By default bin/docker-image-tool.sh builds docker image for running JVM jobs. You need to opt-in to build additional language binding docker images.

Example usage is

# To build additional PySpark docker image
$ ./bin/docker-image-tool.sh -r <repo> -t my-tag -p ./kubernetes/dockerfiles/spark/bindings/python/Dockerfile build

# To build additional SparkR docker image
$ ./bin/docker-image-tool.sh -r <repo> -t my-tag -R ./kubernetes/dockerfiles/spark/bindings/R/Dockerfile build

Cluster Mode

To launch Spark Pi in cluster mode,

$ ./bin/spark-submit \
    --master k8s://https://<k8s-apiserver-host>:<k8s-apiserver-port> \
    --deploy-mode cluster \
    --name spark-pi \
    --class org.apache.spark.examples.SparkPi \
    --conf spark.executor.instances=5 \
    --conf spark.kubernetes.container.image=<spark-image> \
    local:///path/to/examples.jar

The Spark master, specified either via passing the --master command line argument to spark-submit or by setting spark.master in the application’s configuration, must be a URL with the format k8s://<api_server_host>:<k8s-apiserver-port>. The port must always be specified, even if it’s the HTTPS port 443. Prefixing the master string with k8s:// will cause the Spark application to launch on the Kubernetes cluster, with the API server being contacted at api_server_url. If no HTTP protocol is specified in the URL, it defaults to https. For example, setting the master to k8s://example.com:443 is equivalent to setting it to k8s://https://example.com:443, but to connect without TLS on a different port, the master would be set to k8s://http://example.com:8080.

In Kubernetes mode, the Spark application name that is specified by spark.app.name or the --name argument to spark-submit is used by default to name the Kubernetes resources created like drivers and executors. So, application names must consist of lower case alphanumeric characters, -, and . and must start and end with an alphanumeric character.

If you have a Kubernetes cluster setup, one way to discover the apiserver URL is by executing kubectl cluster-info.

$ kubectl cluster-info
Kubernetes master is running at http://127.0.0.1:6443

In the above example, the specific Kubernetes cluster can be used with spark-submit by specifying --master k8s://http://127.0.0.1:6443 as an argument to spark-submit. Additionally, it is also possible to use the authenticating proxy, kubectl proxy to communicate to the Kubernetes API.

The local proxy can be started by:

$ kubectl proxy

If the local proxy is running at localhost:8001, --master k8s://http://127.0.0.1:8001 can be used as the argument to spark-submit. Finally, notice that in the above example we specify a jar with a specific URI with a scheme of local://. This URI is the location of the example jar that is already in the Docker image.

Client Mode

Starting with Spark 2.4.0, it is possible to run Spark applications on Kubernetes in client mode. When your application runs in client mode, the driver can run inside a pod or on a physical host. When running an application in client mode, it is recommended to account for the following factors:

Client Mode Networking

Spark executors must be able to connect to the Spark driver over a hostname and a port that is routable from the Spark executors. The specific network configuration that will be required for Spark to work in client mode will vary per setup. If you run your driver inside a Kubernetes pod, you can use a headless service to allow your driver pod to be routable from the executors by a stable hostname. When deploying your headless service, ensure that the service’s label selector will only match the driver pod and no other pods; it is recommended to assign your driver pod a sufficiently unique label and to use that label in the label selector of the headless service. Specify the driver’s hostname via spark.driver.host and your spark driver’s port to spark.driver.port.

Client Mode Executor Pod Garbage Collection

If you run your Spark driver in a pod, it is highly recommended to set spark.kubernetes.driver.pod.name to the name of that pod. When this property is set, the Spark scheduler will deploy the executor pods with an OwnerReference, which in turn will ensure that once the driver pod is deleted from the cluster, all of the application’s executor pods will also be deleted. The driver will look for a pod with the given name in the namespace specified by spark.kubernetes.namespace, and an OwnerReference pointing to that pod will be added to each executor pod’s OwnerReferences list. Be careful to avoid setting the OwnerReference to a pod that is not actually that driver pod, or else the executors may be terminated prematurely when the wrong pod is deleted.

If your application is not running inside a pod, or if spark.kubernetes.driver.pod.name is not set when your application is actually running in a pod, keep in mind that the executor pods may not be properly deleted from the cluster when the application exits. The Spark scheduler attempts to delete these pods, but if the network request to the API server fails for any reason, these pods will remain in the cluster. The executor processes should exit when they cannot reach the driver, so the executor pods should not consume compute resources (cpu and memory) in the cluster after your application exits.

Authentication Parameters

Use the exact prefix spark.kubernetes.authenticate for Kubernetes authentication parameters in client mode.

Dependency Management

If your application’s dependencies are all hosted in remote locations like HDFS or HTTP servers, they may be referred to by their appropriate remote URIs. Also, application dependencies can be pre-mounted into custom-built Docker images. Those dependencies can be added to the classpath by referencing them with local:// URIs and/or setting the SPARK_EXTRA_CLASSPATH environment variable in your Dockerfiles. The local:// scheme is also required when referring to dependencies in custom-built Docker images in spark-submit. We support dependencies from the submission client’s local file system using the file:// scheme or without a scheme (using a full path), where the destination should be a Hadoop compatible filesystem. A typical example of this using S3 is via passing the following options:

...
--packages com.amazonaws:aws-java-sdk:1.7.4,org.apache.hadoop:hadoop-aws:2.7.6
--conf spark.kubernetes.file.upload.path=s3a://<s3-bucket>/path
--conf spark.hadoop.fs.s3a.access.key=...
--conf spark.hadoop.fs.s3a.impl=org.apache.hadoop.fs.s3a.S3AFileSystem
--conf spark.hadoop.fs.s3a.fast.upload=true
--conf spark.hadoop.fs.s3a.secret.key=....
--conf spark.driver.extraJavaOptions=-Divy.cache.dir=/tmp -Divy.home=/tmp
file:///full/path/to/app.jar

The app jar file will be uploaded to the S3 and then when the driver is launched it will be downloaded to the driver pod and will be added to its classpath. Spark will generate a subdir under the upload path with a random name to avoid conflicts with spark apps running in parallel. User could manage the subdirs created according to his needs.

The client scheme is supported for the application jar, and dependencies specified by properties spark.jars and spark.files.

Important: all client-side dependencies will be uploaded to the given path with a flat directory structure so file names must be unique otherwise files will be overwritten. Also make sure in the derived k8s image default ivy dir has the required access rights or modify the settings as above. The latter is also important if you use --packages in cluster mode.

Secret Management

Kubernetes Secrets can be used to provide credentials for a Spark application to access secured services. To mount a user-specified secret into the driver container, users can use the configuration property of the form spark.kubernetes.driver.secrets.[SecretName]=<mount path>. Similarly, the configuration property of the form spark.kubernetes.executor.secrets.[SecretName]=<mount path> can be used to mount a user-specified secret into the executor containers. Note that it is assumed that the secret to be mounted is in the same namespace as that of the driver and executor pods. For example, to mount a secret named spark-secret onto the path /etc/secrets in both the driver and executor containers, add the following options to the spark-submit command:

--conf spark.kubernetes.driver.secrets.spark-secret=/etc/secrets
--conf spark.kubernetes.executor.secrets.spark-secret=/etc/secrets

To use a secret through an environment variable use the following options to the spark-submit command:

--conf spark.kubernetes.driver.secretKeyRef.ENV_NAME=name:key
--conf spark.kubernetes.executor.secretKeyRef.ENV_NAME=name:key

Pod Template

Kubernetes allows defining pods from template files. Spark users can similarly use template files to define the driver or executor pod configurations that Spark configurations do not support. To do so, specify the spark properties spark.kubernetes.driver.podTemplateFile and spark.kubernetes.executor.podTemplateFile to point to local files accessible to the spark-submit process. To allow the driver pod access the executor pod template file, the file will be automatically mounted onto a volume in the driver pod when it’s created. Spark does not do any validation after unmarshalling these template files and relies on the Kubernetes API server for validation.

It is important to note that Spark is opinionated about certain pod configurations so there are values in the pod template that will always be overwritten by Spark. Therefore, users of this feature should note that specifying the pod template file only lets Spark start with a template pod instead of an empty pod during the pod-building process. For details, see the full list of pod template values that will be overwritten by spark.

Pod template files can also define multiple containers. In such cases, you can use the spark properties spark.kubernetes.driver.podTemplateContainerName and spark.kubernetes.executor.podTemplateContainerName to indicate which container should be used as a basis for the driver or executor. If not specified, or if the container name is not valid, Spark will assume that the first container in the list will be the driver or executor container.

Using Kubernetes Volumes

Starting with Spark 2.4.0, users can mount the following types of Kubernetes volumes into the driver and executor pods:

• hostPath: mounts a file or directory from the host node’s filesystem into a pod.
• emptyDir: an initially empty volume created when a pod is assigned to a node.
• persistentVolumeClaim: used to mount a PersistentVolume into a pod.

NB: Please see the Security section of this document for security issues related to volume mounts.

To mount a volume of any of the types above into the driver pod, use the following configuration property:

--conf spark.kubernetes.driver.volumes.[VolumeType].[VolumeName].mount.path=<mount path>
--conf spark.kubernetes.driver.volumes.[VolumeType].[VolumeName].mount.readOnly=<true|false>
--conf spark.kubernetes.driver.volumes.[VolumeType].[VolumeName].mount.subPath=<mount subPath>

Specifically, VolumeType can be one of the following values: hostPath, emptyDir, and persistentVolumeClaim. VolumeName is the name you want to use for the volume under the volumes field in the pod specification.

Each supported type of volumes may have some specific configuration options, which can be specified using configuration properties of the following form:

spark.kubernetes.driver.volumes.[VolumeType].[VolumeName].options.[OptionName]=<value>

For example, the claim name of a persistentVolumeClaim with volume name checkpointpvc can be specified using the following property:

spark.kubernetes.driver.volumes.persistentVolumeClaim.checkpointpvc.options.claimName=check-point-pvc-claim

The configuration properties for mounting volumes into the executor pods use prefix spark.kubernetes.executor. instead of spark.kubernetes.driver.. For a complete list of available options for each supported type of volumes, please refer to the Spark Properties section below.

Local Storage

Spark supports using volumes to spill data during shuffles and other operations. To use a volume as local storage, the volume’s name should starts with spark-local-dir-, for example:

--conf spark.kubernetes.driver.volumes.[VolumeType].spark-local-dir-[VolumeName].mount.path=<mount path>
--conf spark.kubernetes.driver.volumes.[VolumeType].spark-local-dir-[VolumeName].mount.readOnly=false

If no volume is set as local storage, Spark uses temporary scratch space to spill data to disk during shuffles and other operations. When using Kubernetes as the resource manager the pods will be created with an emptyDir volume mounted for each directory listed in spark.local.dir or the environment variable SPARK_LOCAL_DIRS . If no directories are explicitly specified then a default directory is created and configured appropriately.

emptyDir volumes use the ephemeral storage feature of Kubernetes and do not persist beyond the life of the pod.

Using RAM for local storage

emptyDir volumes use the nodes backing storage for ephemeral storage by default, this behaviour may not be appropriate for some compute environments. For example if you have diskless nodes with remote storage mounted over a network, having lots of executors doing IO to this remote storage may actually degrade performance.

In this case it may be desirable to set spark.kubernetes.local.dirs.tmpfs=true in your configuration which will cause the emptyDir volumes to be configured as tmpfs i.e. RAM backed volumes. When configured like this Spark’s local storage usage will count towards your pods memory usage therefore you may wish to increase your memory requests by increasing the value of spark.kubernetes.memoryOverheadFactor as appropriate.

Introspection and Debugging

These are the different ways in which you can investigate a running/completed Spark application, monitor progress, and take actions.

Accessing Logs

Logs can be accessed using the Kubernetes API and the kubectl CLI. When a Spark application is running, it’s possible to stream logs from the application using:

$ kubectl -n=<namespace> logs -f <driver-pod-name>

The same logs can also be accessed through the Kubernetes dashboard if installed on the cluster.

Accessing Driver UI

The UI associated with any application can be accessed locally using kubectl port-forward.

$ kubectl port-forward <driver-pod-name> 4040:4040

Then, the Spark driver UI can be accessed on http://localhost:4040.

Debugging

There may be several kinds of failures. If the Kubernetes API server rejects the request made from spark-submit, or the connection is refused for a different reason, the submission logic should indicate the error encountered. However, if there are errors during the running of the application, often, the best way to investigate may be through the Kubernetes CLI.

To get some basic information about the scheduling decisions made around the driver pod, you can run:

$ kubectl describe pod <spark-driver-pod>

If the pod has encountered a runtime error, the status can be probed further using:

$ kubectl logs <spark-driver-pod>

Status and logs of failed executor pods can be checked in similar ways. Finally, deleting the driver pod will clean up the entire spark application, including all executors, associated service, etc. The driver pod can be thought of as the Kubernetes representation of the Spark application.

Kubernetes Features

Configuration File

Your Kubernetes config file typically lives under .kube/config in your home directory or in a location specified by the KUBECONFIG environment variable. Spark on Kubernetes will attempt to use this file to do an initial auto-configuration of the Kubernetes client used to interact with the Kubernetes cluster. A variety of Spark configuration properties are provided that allow further customising the client configuration e.g. using an alternative authentication method.

Contexts

Kubernetes configuration files can contain multiple contexts that allow for switching between different clusters and/or user identities. By default Spark on Kubernetes will use your current context (which can be checked by running kubectl config current-context) when doing the initial auto-configuration of the Kubernetes client.

In order to use an alternative context users can specify the desired context via the Spark configuration property spark.kubernetes.context e.g. spark.kubernetes.context=minikube.

Namespaces

Kubernetes has the concept of namespaces. Namespaces are ways to divide cluster resources between multiple users (via resource quota). Spark on Kubernetes can use namespaces to launch Spark applications. This can be made use of through the spark.kubernetes.namespace configuration.

Kubernetes allows using ResourceQuota to set limits on resources, number of objects, etc on individual namespaces. Namespaces and ResourceQuota can be used in combination by administrator to control sharing and resource allocation in a Kubernetes cluster running Spark applications.

RBAC

In Kubernetes clusters with RBAC enabled, users can configure Kubernetes RBAC roles and service accounts used by the various Spark on Kubernetes components to access the Kubernetes API server.

The Spark driver pod uses a Kubernetes service account to access the Kubernetes API server to create and watch executor pods. The service account used by the driver pod must have the appropriate permission for the driver to be able to do its work. Specifically, at minimum, the service account must be granted a Role or ClusterRole that allows driver pods to create pods and services. By default, the driver pod is automatically assigned the default service account in the namespace specified by spark.kubernetes.namespace, if no service account is specified when the pod gets created.

Depending on the version and setup of Kubernetes deployed, this default service account may or may not have the role that allows driver pods to create pods and services under the default Kubernetes RBAC policies. Sometimes users may need to specify a custom service account that has the right role granted. Spark on Kubernetes supports specifying a custom service account to be used by the driver pod through the configuration property spark.kubernetes.authenticate.driver.serviceAccountName=<service account name>. For example, to make the driver pod use the spark service account, a user simply adds the following option to the spark-submit command:

--conf spark.kubernetes.authenticate.driver.serviceAccountName=spark

To create a custom service account, a user can use the kubectl create serviceaccount command. For example, the following command creates a service account named spark:

$ kubectl create serviceaccount spark

To grant a service account a Role or ClusterRole, a RoleBinding or ClusterRoleBinding is needed. To create a RoleBinding or ClusterRoleBinding, a user can use the kubectl create rolebinding (or clusterrolebinding for ClusterRoleBinding) command. For example, the following command creates an edit ClusterRole in the default namespace and grants it to the spark service account created above:

$ kubectl create clusterrolebinding spark-role --clusterrole=edit --serviceaccount=default:spark --namespace=default

Note that a Role can only be used to grant access to resources (like pods) within a single namespace, whereas a ClusterRole can be used to grant access to cluster-scoped resources (like nodes) as well as namespaced resources (like pods) across all namespaces. For Spark on Kubernetes, since the driver always creates executor pods in the same namespace, a Role is sufficient, although users may use a ClusterRole instead. For more information on RBAC authorization and how to configure Kubernetes service accounts for pods, please refer to Using RBAC Authorization and Configure Service Accounts for Pods.

Spark Application Management

Kubernetes provides simple application management via the spark-submit CLI tool in cluster mode. Users can kill a job by providing the submission ID that is printed when submitting their job. The submission ID follows the format namespace:driver-pod-name. If user omits the namespace then the namespace set in current k8s context is used. For example if user has set a specific namespace as follows kubectl config set-context minikube --namespace=spark then the spark namespace will be used by default. On the other hand, if there is no namespace added to the specific context then all namespaces will be considered by default. That means operations will affect all Spark applications matching the given submission ID regardless of namespace. Moreover, spark-submit for application management uses the same backend code that is used for submitting the driver, so the same properties like spark.kubernetes.context etc., can be re-used.

For example:

$ spark-submit --kill spark:spark-pi-1547948636094-driver --master k8s://https://192.168.2.8:8443

Users also can list the application status by using the --status flag:

$ spark-submit --status spark:spark-pi-1547948636094-driver --master  k8s://https://192.168.2.8:8443

Both operations support glob patterns. For example user can run:

$ spark-submit --kill spark:spark-pi* --master  k8s://https://192.168.2.8:8443

The above will kill all application with the specific prefix.

User can specify the grace period for pod termination via the spark.kubernetes.appKillPodDeletionGracePeriod property, using --conf as means to provide it (default value for all K8s pods is 30 secs).

Future Work

There are several Spark on Kubernetes features that are currently being worked on or planned to be worked on. Those features are expected to eventually make it into future versions of the spark-kubernetes integration.

Some of these include:

• Dynamic Resource Allocation and External Shuffle Service
• Job Queues and Resource Management

Configuration

See the configuration page for information on Spark configurations. The following configurations are specific to Spark on Kubernetes.

Spark Properties

Pod template properties

See the below table for the full list of pod specifications that will be overwritten by spark.

Pod Metadata

Pod Spec

Container spec

The following affect the driver and executor containers. All other containers in the pod spec will be unaffected.

Resource Allocation and Configuration Overview

Please make sure to have read the Custom Resource Scheduling and Configuration Overview section on the configuration page. This section only talks about the Kubernetes specific aspects of resource scheduling.

The user is responsible to properly configuring the Kubernetes cluster to have the resources available and ideally isolate each resource per container so that a resource is not shared between multiple containers. If the resource is not isolated the user is responsible for writing a discovery script so that the resource is not shared between containers. See the Kubernetes documentation for specifics on configuring Kubernetes with custom resources.

Spark automatically handles translating the Spark configs spark.{driver/executor}.resource.{resourceType} into the kubernetes configs as long as the Kubernetes resource type follows the Kubernetes device plugin format of vendor-domain/resourcetype. The user must specify the vendor using the spark.{driver/executor}.resource.{resourceType}.vendor config. The user does not need to explicitly add anything if you are using Pod templates. For reference and an example, you can see the Kubernetes documentation for scheduling GPUs. Spark only supports setting the resource limits.

Kubernetes does not tell Spark the addresses of the resources allocated to each container. For that reason, the user must specify a discovery script that gets run by the executor on startup to discover what resources are available to that executor. You can find an example scripts in examples/src/main/scripts/getGpusResources.sh. The script must have execute permissions set and the user should setup permissions to not allow malicious users to modify it. The script should write to STDOUT a JSON string in the format of the ResourceInformation class. This has the resource name and an array of resource addresses available to just that executor.