pod-running-checker

Description

A POSIX shell script based container: It that calls the Kubernetes API to check running Pods matching the desired Labels.

Purpose

Useful as InitContainer in Kubernetes to create dependendencies between deployments, as it could check if another deployment is Running by matching labels and status, before starting to rollout the dependency

It will check for pods running with certain labels

LABELS="app=alpine,pod-template-hash=7b421232"

It supports for WAIT_TIME and default is 10 seconds

WAIT_TIME=10

It will not time out, useful to keep the default timeout of a deplomyent or a helm update

Cluster Permissions

In order to be able to operate, this pod needs to have some permissions and query the Kubernetes API, this could be done by creating a Service Account and Cluster Role

Is already a deprecrated way to use ClusterRole and ClusterRoleBinding since v1.17

Be aware about the namespace where you define it

apiVersion: v1
kind: ServiceAccount
metadata:
  name: pod-running-checker
  namespace: default
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: pod-running-checker
rules:
  - apiGroups:
      - ""
    resources:
      - pods
      - services
      - endpoints
    verbs:
      - get
      - list
      - watch
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: system:serviceaccount:pod-running-checker:default
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: pod-running-checker
subjects:
- kind: ServiceAccount
  name: pod-running-checker
  namespace: default

Deployment example

This nginx-deployment will rollout when at least one Pod with labels app=alpine and pod-template-hash=7b421232 is on Running state

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      serviceAccountName: pod-running-checker
      initContainers:
        - name: pod-running-checker
          securityContext:
            {}
          image: piscue/pod-running-checker:0.1.2
          imagePullPolicy: IfNotPresent
          env:
            - name: LABELS
              value: "app=alpine,pod-template-hash=7b421232"
      containers:
        - name: nginx
          image: nginx:latest
          ports:
            - name: http
              containerPort: 80
              protocol: TCP