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Kubernetes Services

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David Maier edited this page Sep 20, 2016 · 8 revisions

There are multiple kinds of services. Services are there in order to expose access (internal or external) to Pods. Let's assume that we labeled some pods with 'couchbase-cluster', then the following descriptor would expose the Couchbase Admin port internally:

apiVersion: v1
kind: Service
metadata:
  name: couchbase-cluster-int
  labels:
    name: couchbase-cluster
spec:
  ports:
  - port: 8091
  selector:
    name: couchbase-cluster

In order to register our service, the following command can be issued:

kubectl.sh create -f couchbase-service-internal.yaml

In order to list our services, we can then use:

david@steambox:~/Git/dmaier-couchbase/cb-openshift3/examples/k8s$ kubectl.sh get services -l name=couchbase-cluster
NAME                    CLUSTER-IP       EXTERNAL-IP   PORT(S)    AGE
couchbase-cluster-int   10.247.202.160   <none>        8091/TCP   5m

The discovery works via environment variables:

david@steambox:~/Git/dmaier-couchbase/cb-openshift3/examples/k8s$ kubectl.sh exec couchbase-cluster-hhb2z -- env | grep COUCHBASE_CLUSTER_INT
COUCHBASE_CLUSTER_INT_SERVICE_HOST=10.247.202.160
COUCHBASE_CLUSTER_INT_PORT_8091_TCP_ADDR=10.247.202.160
COUCHBASE_CLUSTER_INT_PORT_8091_TCP_PROTO=tcp
COUCHBASE_CLUSTER_INT_PORT_8091_TCP_PORT=8091
COUCHBASE_CLUSTER_INT_PORT_8091_TCP=tcp://10.247.202.160:8091
COUCHBASE_CLUSTER_INT_SERVICE_PORT=8091
COUCHBASE_CLUSTER_INT_PORT=tcp://10.247.202.160:8091

Kube-Proxy

The idea of services is that (as far as I understand) they are exposed via a Kube-Proxy (running on the minion node). This is usually a very good thing because it decouples the access to a specific endpoint from the actual instances those are providing it. Means that this proxy just forwards the access to several endpoints. Our 3 node replica set then causes 3 endpoints those are only accessible via Kube-Proxy:

Name:			couchbase-cluster-int
Namespace:		default
Labels:			name=couchbase-cluster
Selector:		name=couchbase-cluster
Type:			ClusterIP
IP:			10.247.202.160
Port:			<unset>	8091/TCP
Endpoints:		10.246.34.5:8091,10.246.34.6:8091,10.246.34.7:8091
Session Affinity:	None
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