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Using external services inside Kubernetes

 

Components

Networks

• Host network: 192.168.0.0/24
• Service network: 10.0.0.0/16
• Pod network: 172.16.0.0/16

Hosts

• master01: 192.168.0.1
• master02: 192.168.0.2
• master03: 192.168.0.3
• pgsql-master: 192.168.0.10
• pgsql-slave: 192.168.0.11

Services

• kubernetes: 10.0.0.1
• dns: 10.0.0.254

“Normal” flow

External services

Configuration way

export DATABASE_URL='postgresql://application@192.168.0.10:5432/production_db'

WRONG

Database failure

export DATABASE_URL='postgresql://application@192.168.0.11:5432/production_db'

• You should resetup ALL related deployments and restart ALL theirs pods for hosted service address reconfiguration

DNS way

postgres IN A 192.168.0.10

export DATABASE_URL="postgresql://application@postgres.somezone.tld:5432/production_db"

WRONG!

Database failure

• update DNS record
• Remember about DNS cache
• Actually it is easier to kill all related pods

External services. The right way

Use force endpoints and services, Luke!

Obvious example

$ kubectl get endpoints kubernetes
NAME         ENDPOINTS                                            AGE
kubernetes   192.168.0.1:8443,192.168.0.2:8443,192.168.0.3:8443   1y

$ kubectl get service kubernetes
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.0.0.1     none          443/TCP   1y

In YAML: endpoint

apiVersion: v1
kind: Endpoints
metadata:
  name: kubernetes
  namespace: default
subsets:
- addresses:
  - ip: 192.168.0.1
  - ip: 192.168.0.2
  - ip: 192.168.0.3
  ports:
  - name: https
    port: 8443
    protocol: TCP

In YAML: service

apiVersion: v1
kind: Service
metadata:
  labels:
    component: apiserver
    provider: kubernetes
  name: kubernetes
  namespace: default
spec:
  clusterIP: 10.0.0.1
  ports:
  - name: https
    port: 443
    protocol: TCP
    targetPort: 8443
  type: ClusterIP

Back to PostgreSQL

Endpoint

apiVersion: v1
kind: Endpoints
metadata:
  name: postgres
  namespace: hosted
subsets:
- addresses:
  - ip: 192.168.0.10
  ports:
  - name: postgres
    port: 5432
    protocol: TCP

Service

apiVersion: v1
kind: Service
metadata:
  name: postgres
  namespace: hosted
spec:
  ports:
  - name: postgres
    port: 5432
    protocol: TCP
    targetPort: 5432
  type: ClusterIP

Configuration

export DATABASE_URL='postgresql://application@postgres.hosted.cluster.local:5432/production_db'

RIGHT!

• Service address is rock solid
• Service IP can be preserved in service manifest
• Any host network reconfiguration is just endpoint upgrade
• Endpoint upgrade is rocket fast - kube-proxy rocks!

Questions?