NEXUS

NEXUS is an earth science data analytics application, and a component of the Apache Science Data Analytics Platform (SDAP).

Introduction

The helm chart deploys all the required components of the NEXUS application (Spark webapp, Solr, Cassandra, Zookeeper, and optionally ingress components).

Table of Contents

• Prerequisites
  • Spark Operator
  • Persistent Volume Provisioner
• Installing the Chart
• Verifying Successful Installation
  • Local Deployment with Ingress Enabled
  • No Ingress Enabled
• Uninstalling the Chart
• Configuration
• Restricting Pods to Specific Nodes

Prerequisites

• Kubernetes 1.9+
• Spark Operator
• Storage class and persistent volume provisioner in the underlying infrastructure

Spark Operator

NEXUS needs the Spark Operator in order to run. Follow their instructions to install the Helm chart, or simply run:

$ kubectl create namespace spark-operator
$ helm repo add incubator http://storage.googleapis.com/kubernetes-charts-incubator
$ helm install incubator/sparkoperator --generate-name --namespace=spark-operator

Persistent Volume Provisioner

NEXUS stores data in Cassandra and Solr. In order to have persistent storage, you need to have a Storage Class defined and have Persistent Volumes provisioned either manually or dynamically. See Persistent Volumes.

Tip: If you are using an NFS server as storage, you can use nfs-client-provisioner to dynamically provision persistent volumes on your NFS server.

Installing the Chart

First clone the NEXUS repository.

$ git clone https://github.com/apache/incubator-sdap-nexus.git

Then install the Helm chart.

$ kubectl create namespace sdap
$ helm install nexus incubator-sdap-nexus/helm --namespace=sdap --dependency-update

Tip: It may take a few minutes for the nexus-webapp-driver pod to start up because this depends on Solr and Cassandra being accessible.

Verifying Successful Installation

Check that all the pods are up by running kubectl get pods -n sdap, and make sure all pods have status Running. If any pods have not started within a few minutes, you can look at its status with `kubectl describe pod -n sdap.

Option 1: Local deployment with ingress enabled

If you have installed the Helm chart locally with ingressEnabled set to true (see ingressEnabled under Configuration), you can verify the installation by requesting the list endpoint. If this returns an HTTP 200 response, Nexus is healthy.

$ curl localhost/nexus/list

Option 2: No ingress enabled

If you have installed the Helm chart on a cloud provider, and/or have not enabled a loadbalancer with ingressEnabled=true, you can temporarily port-forward the nexus-webapp port to see if the webapp responds.

First, on the Kubernetes cluster or jump host, create a port-forward to the nexus-webapp service:

$ kubectl port-forward service/nexus-webapp -n sdap 8083:8083

Then open another shell on the same host and request the list endpoint through the forwarded port:

$ curl localhost:8083/list

Note: In this case the list endpoint is /list instead of /nexus/list because we are connecting to the nexus-webapp service directly, instead of through an ingress rule.

If the request returns an HTTP 200 response, NEXUS is healthy. You can now close the first shell to disable the port-forward.

If one of the pods or deployment is not started, you can look at its status with:

kubectl describe pod <pod-name> -n sdap

Uninstalling the Chart

To uninstall/delete the nexus deployment:

$ helm delete nexus -n sdap

The command removes all the Kubernetes components associated with the chart and deletes the release.

Configuration

There are two ways to override configuration values for the chart. The first is to use the --set flag when installing the chart, for example:

$ helm install nexus incubator-sdap-nexus/helm --namespace=sdap --dependency-update --set cassandra.replicas=3 --set solr.replicas=3

The second way is to create a yaml file with overridden configuration values and pass it in with the -f flag during chart installation.

# overridden-values.yml

cassandra:
  replicas: 2
solr:
  replicas: 2

$ helm install nexus incubator-sdap-nexus/helm --namespace=sdap --dependency-update -f ~/overridden-values.yml

The following table lists the configurable parameters of the NEXUS chart and their default values. You can also look at helm/values.yaml to see the available options.

Note: The default configuration values are tuned to run NEXUS in a local environment. Setting ingressEnabled=true in addition will create a load balancer and expose NEXUS at localhost.

Restricting Pods to Specific Nodes

Sometimes you may wish to restrict pods to run on specific nodes, for example if you have “UAT” and “SIT” nodes within the same cluster. You can configure node selectors and tolerations for all the components, as in the following example:

webapp:
  distributed:
    driver:
      tolerations:
        - key: environment
          operator: Equal
          value: uat
          effect: NoExecute
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: environment
                operator: In
                values:
                - uat
    executor:
      tolerations:
        - key: environment
          operator: Equal
          value: uat
          effect: NoExecute
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: environment
                operator: In
                values:
                - uat

cassandra:
  tolerations:
    - key: environment
      operator: Equal
      value: uat
      effect: NoExecute
  nodeSelector:
    environment: uat 

solr:
  tolerations:
    - key: environment
      operator: Equal
      value: uat
      effect: NoExecute
  nodeSelector:
    environment: uat 

zookeeper:
  tolerations:
    - key: environment
      operator: Equal
      value: uat
      effect: NoExecute
  nodeSelector:
    environment: uat 

Note: The webapp supports affinity instead of nodeSelector because the Spark Operator has deprecated nodeSelector in favor of affinity.