water.k8s.lookup

Class KubernetesDnsLookup

java.lang.Object

water.k8s.lookup.KubernetesDnsLookup

All Implemented Interfaces:

KubernetesLookup

public class KubernetesDnsLookup
extends java.lang.Object
implements KubernetesLookup

Discovery strategy on a DNS cluster leveraging the DNS record of a Kubernetes headless service present in the cluster. Kubernetes headless services, instead of load-balancing the requests onto one of the underlying pods, return the addresses of all the pods covered by the headless service.

Such pods can then be discovered via the above-mentioned DNS record. In order for H2O to know which service to query, it is mandatory for the K8S user to pass the name of the headless service to the H2O container, as follows:

 apiVersion: apps/v1
 kind: StatefulSet
 metadata:
   name: h2o-stateful-set
   namespace: h2o-statefulset
 spec:
   serviceName: h2o-service
   replicas: 3
   selector:
     matchLabels:
       app: h2o-k8s
   template:
     metadata:
       labels:
         app: h2o-k8s
     spec:
       terminationGracePeriodSeconds: 10
       containers:
         - name: h2o-k8s
           image: ''
           resources:
             requests:
               memory: "4Gi"
           ports:
             - containerPort: 54321
               protocol: TCP
           env:
           - name: H2O_KUBERNETES_SERVICE_DNS
             value: h2o-service.h2o-statefulset.svc.cluster.local
           - name: H2O_NODE_LOOKUP_TIMEOUT
             value: '180'
           - name: H2O_NODE_EXPECTED_COUNT
             value: '3'
 

Constructor Summary

Constructors

Constructor and Description
KubernetesDnsLookup(java.lang.String serviceDns)

Method Summary

Modifier and Type	Method and Description
static KubernetesDnsLookup	fromH2ODefaults()
static boolean	isLookupPossible()
java.util.Optional<java.util.Set<java.lang.String>>	lookupNodes(java.util.Collection<LookupConstraint> lookupConstraints) Looks up H2O pods via configured K8S Stateless service DNS.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

KubernetesDnsLookup

public KubernetesDnsLookup(java.lang.String serviceDns)

Method Detail

fromH2ODefaults

public static KubernetesDnsLookup fromH2ODefaults()
                                           throws java.lang.IllegalStateException

Returns:

Throws:

java.lang.IllegalStateException - When the H2O-related kubernetes DNS service is not found

lookupNodes

public java.util.Optional<java.util.Set<java.lang.String>> lookupNodes(java.util.Collection<LookupConstraint> lookupConstraints)

Looks up H2O pods via configured K8S Stateless service DNS. Environment variable with key defined in H2O_K8S_SERVICE_DNS_KEY constant is used to obtain address of the DNS. The DNS is then queried for pods in the underlying service. It is the responsibility of the K8S cluster owner to set-up the service correctly to only provide correct adresses of pods with H2O active. If pods with no H2O running are supplied, the resulting flatfile may contain pod IPs with no H2O running as well.

Specified by:

lookupNodes in interface KubernetesLookup

Parameters:

lookupConstraints - Constraints to obey during lookup

Returns:

A Set of adresses of looked up nodes represented as String. The resulting set is never empty.

isLookupPossible

public static boolean isLookupPossible()