KubeDirector: The easy way to run complex stateful applications on Kubernetes

Wednesday, October 03, 2018

KubeDirector: The easy way to run complex stateful applications on Kubernetes

Author: Thomas Phelan (BlueData)

KubeDirector is an open source project designed to make it easy to run complex stateful scale-out application clusters on Kubernetes.

KubeDirector is built using the custom resource definition (CRD) framework and leverages the native Kubernetes API extensions and design philosophy. This enables transparent integration with Kubernetes user/resource management as well as existing clients and tools.

We recently introduced the KubeDirector project, as part of a broader open source Kubernetes initiative we call BlueK8s. I’m happy to announce that the pre-alpha code for KubeDirector is now available. And in this blog post, I’ll show how it works.

KubeDirector provides the following capabilities: * The ability to run non-cloud native stateful applications on Kubernetes without modifying the code. In other words, it’s not necessary to decompose these existing applications to fit a microservices design pattern. * Native support for preserving application-specific configuration and state. * An application-agnostic deployment pattern, minimizing the time to onboard new stateful applications to Kubernetes.

KubeDirector enables data scientists familiar with data-intensive distributed applications such as Hadoop, Spark, Cassandra, TensorFlow, Caffe2, etc. to run these applications on Kubernetes – with a minimal learning curve and no need to write GO code. The applications controlled by KubeDirector are defined by some basic metadata and an associated package of configuration artifacts. The application metadata is referred to as a KubeDirectorApp resource.

To understand the components of KubeDirector, clone the repository on GitHub using a command similar to:

git clone http://<userid>@github.com/bluek8s/kubedirector.

The KubeDirectorApp definition for the Spark 2.2.1 application is located in the file kubedirector/deploy/example_catalog/cr-app-spark221e2.json.

 ~> cat kubedirector/deploy/example_catalog/cr-app-spark221e2.json
 {
    "apiVersion": "kubedirector.bluedata.io/v1alpha1",
    "kind": "KubeDirectorApp",
    "metadata": {
        "name" : "spark221e2"
    },
    "spec" : {
        "systemctlMounts": true,
        "config": {
            "node_services": [
                {
                    "service_ids": [
                        "ssh",
                        "spark",
                        "spark_master",
                        "spark_worker"
                    ],
…

The configuration of an application cluster is referred to as a KubeDirectorCluster resource. The KubeDirectorCluster definition for a sample Spark 2.2.1 cluster is located in the file kubedirector/deploy/example_clusters/cr-cluster-spark221.e1.yaml.

~> cat kubedirector/deploy/example_clusters/cr-cluster-spark221.e1.yaml
apiVersion: "kubedirector.bluedata.io/v1alpha1"
kind: "KubeDirectorCluster"
metadata:
  name: "spark221e2"
spec:
  app: spark221e2
  roles:
  - name: controller
    replicas: 1
    resources:
      requests:
        memory: "4Gi"
        cpu: "2"
      limits:
        memory: "4Gi"
        cpu: "2"
  - name: worker
    replicas: 2
    resources:
      requests:
        memory: "4Gi"
        cpu: "2"
      limits:
        memory: "4Gi"
        cpu: "2"
  - name: jupyter
…

Running Spark on Kubernetes with KubeDirector

With KubeDirector, it’s easy to run Spark clusters on Kubernetes.

First, verify that Kubernetes (version 1.9 or later) is running, using the command kubectl version

~> kubectl version
Client Version: version.Info{Major:"1", Minor:"11", GitVersion:"v1.11.3", GitCommit:"a4529464e4629c21224b3d52edfe0ea91b072862", GitTreeState:"clean", BuildDate:"2018-09-09T18:02:47Z", GoVersion:"go1.10.3", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"11", GitVersion:"v1.11.3", GitCommit:"a4529464e4629c21224b3d52edfe0ea91b072862", GitTreeState:"clean", BuildDate:"2018-09-09T17:53:03Z", GoVersion:"go1.10.3", Compiler:"gc", Platform:"linux/amd64"}                                    

Deploy the KubeDirector service and the example KubeDirectorApp resource definitions with the commands:

cd kubedirector
make deploy

These will start the kubedirector pod:

~> kubectl get pods
NAME                           READY     STATUS     RESTARTS     AGE
kubedirector-58cf59869-qd9hb   1/1       Running    0            1m     

List the installed kubedirector applications with kubectl get KubeDirectorApp

~> kubectl get KubeDirectorApp
NAME           AGE
cassandra311   30m
spark211up     30m
spark221e2     30m

Now you can launch a Spark 2.2.1 cluster using the example KubeDirectorCluster file and the kubectl create -f deploy/example_clusters/cr-cluster-spark211up.yaml command. Verify that the spark cluster has been started:

~> kubectl get pods
NAME                             READY     STATUS    RESTARTS   AGE
kubedirector-58cf59869-djdwl     1/1       Running   0          19m
spark221e2-controller-zbg4d-0    1/1       Running   0          23m
spark221e2-jupyter-2km7q-0       1/1       Running   0          23m
spark221e2-worker-4gzbz-0        1/1       Running   0          23m
spark221e2-worker-4gzbz-1        1/1       Running   0          23m

The running services now include the spark services:

~> kubectl get service
NAME                                TYPE         CLUSTER-IP        EXTERNAL-IP    PORT(S)                                                    AGE
kubedirector                        ClusterIP    10.98.234.194     <none>         60000/TCP                                                  1d
kubernetes                          ClusterIP    10.96.0.1         <none>         443/TCP                                                    1d
svc-spark221e2-5tg48                ClusterIP    None              <none>         8888/TCP                                                   21s
svc-spark221e2-controller-tq8d6-0   NodePort     10.104.181.123    <none>         22:30534/TCP,8080:31533/TCP,7077:32506/TCP,8081:32099/TCP  20s
svc-spark221e2-jupyter-6989v-0      NodePort     10.105.227.249    <none>         22:30632/TCP,8888:30355/TCP                                20s
svc-spark221e2-worker-d9892-0       NodePort     10.107.131.165    <none>         22:30358/TCP,8081:32144/TCP                                20s
svc-spark221e2-worker-d9892-1       NodePort     10.110.88.221     <none>         22:30294/TCP,8081:31436/TCP                                20s

Pointing the browser at port 31533 connects to the Spark Master UI:

kubedirector

That’s all there is to it! In fact, in the example above we also deployed a Jupyter notebook along with the Spark cluster.

To start another application (e.g. Cassandra), just specify another KubeDirectorApp file:

kubectl create -f deploy/example_clusters/cr-cluster-cassandra311.yaml

See the running cassandra cluster:

~> kubectl get pods
NAME                              READY     STATUS    RESTARTS   AGE
cassandra311-seed-v24r6-0         1/1       Running   0          1m
cassandra311-seed-v24r6-1         1/1       Running   0          1m
cassandra311-worker-rqrhl-0       1/1       Running   0          1m
cassandra311-worker-rqrhl-1       1/1       Running   0          1m
kubedirector-58cf59869-djdwl      1/1       Running   0          1d
spark221e2-controller-tq8d6-0     1/1       Running   0          22m
spark221e2-jupyter-6989v-0        1/1       Running   0          22m
spark221e2-worker-d9892-0         1/1       Running   0          22m
spark221e2-worker-d9892-1         1/1       Running   0          22m

Now you have a Spark cluster (with a Jupyter notebook) and a Cassandra cluster running on Kubernetes. Use kubectl get service to see the set of services.

~> kubectl get service
NAME                                TYPE         CLUSTER-IP       EXTERNAL-IP   PORT(S)                                                   AGE
kubedirector                        ClusterIP    10.98.234.194    <none>        60000/TCP                                                 1d
kubernetes                          ClusterIP    10.96.0.1        <none>        443/TCP                                                   1d
svc-cassandra311-seed-v24r6-0       NodePort     10.96.94.204     <none>        22:31131/TCP,9042:30739/TCP                               3m
svc-cassandra311-seed-v24r6-1       NodePort     10.106.144.52    <none>        22:30373/TCP,9042:32662/TCP                               3m
svc-cassandra311-vhh29              ClusterIP    None             <none>        8888/TCP                                                  3m
svc-cassandra311-worker-rqrhl-0     NodePort     10.109.61.194    <none>        22:31832/TCP,9042:31962/TCP                               3m
svc-cassandra311-worker-rqrhl-1     NodePort     10.97.147.131    <none>        22:31454/TCP,9042:31170/TCP                               3m
svc-spark221e2-5tg48                ClusterIP    None             <none>        8888/TCP                                                  24m
svc-spark221e2-controller-tq8d6-0   NodePort     10.104.181.123   <none>        22:30534/TCP,8080:31533/TCP,7077:32506/TCP,8081:32099/TCP 24m
svc-spark221e2-jupyter-6989v-0      NodePort     10.105.227.249   <none>        22:30632/TCP,8888:30355/TCP                               24m
svc-spark221e2-worker-d9892-0       NodePort     10.107.131.165   <none>        22:30358/TCP,8081:32144/TCP                               24m
svc-spark221e2-worker-d9892-1       NodePort     10.110.88.221    <none>        22:30294/TCP,8081:31436/TCP                               24m

Get Involved

KubeDirector is a fully open source, Apache v2 licensed, project – the first of multiple open source projects within a broader initiative we call BlueK8s. The pre-alpha code for KubeDirector has just been released and we would love for you to join the growing community of developers, contributors, and adopters. Follow @BlueK8s on Twitter and get involved through these channels: