A sidecar container for labeling an active-passive kubernetes workload using kubernetes lease mechanism.
We need a service account with rbac rules for the container to be able to set the pod label
apiVersion: v1
automountServiceAccountToken: true
kind: ServiceAccount
metadata:
name: apsc-test
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
name: apsc
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: Role
name: apsc
subjects:
- kind: ServiceAccount
name: apsc-test
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
name: apsc
rules:
- apiGroups: [ "coordination.k8s.io" ]
resources: [ "leases" ]
verbs: [ "*" ]
- apiGroups: [ "" ]
resources: [ "pods" ]
verbs: [ "get", "list" ]
- apiGroups: [ "" ]
resources: [ "pods" ]
verbs: [ "update" ]The container needs its pod's name and namespace to function, we can parse those using env with fieldRefs.
Furthermore, the label key can be set via LABEL_KEY env variable - it defaults to apsc.knoppiks.de/state and will be
set to active on the leading pod.
apiVersion: apps/v1
kind: Deployment
metadata:
name: apsc-test
spec:
replicas: 2
strategy:
type: RollingUpdate
selector:
matchLabels:
app.kubernetes.io/name: apsc-test
app.kubernetes.io/component: server
template:
metadata:
labels:
app.kubernetes.io/name: apsc-test
app.kubernetes.io/component: server
spec:
automountServiceAccountToken: true
serviceAccountName: apsc-test
containers:
- name: server
image: httpd:2.4-alpine
ports:
- name: http
containerPort: 80
readinessProbe:
httpGet:
port: http
livenessProbe:
httpGet:
port: http
- name: apsc
image: knoppiks/apsc
imagePullPolicy: Always
env:
- name: POD_NAME
valueFrom:
fieldRef:
fieldPath: metadata.name
- name: POD_NAMESPACE
valueFrom:
fieldRef:
fieldPath: metadata.namespace
- name: LABEL_KEY
value: "example.com/state"We can now select the extra label in our service, so that traffic is only sent to the active instance.
---
apiVersion: v1
kind: Service
metadata:
name: apsc-test
spec:
ports:
- name: http
port: 80
targetPort: http
selector:
app.kubernetes.io/name: apsc-test
app.kubernetes.io/component: server
example.com/state: active
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