Kubernetes Deployment Checker

This application is designed to run as a Kubernetes Init Container.

It blocks your application from running until another deployment has reached it's target Ready state.

Usage

There are three command line arguments that you can pass to this application:

Command	Notes
-deployment	Name of Deployment to monitor
-namespace	Namespace of Deployment to monitor
-sleep	Number of seconds between checking the Deployment (default: 10)

Deployment

First, we need to ensure that the init container has privileges to access the specific parts of the Kubernetes API to do it's job:

# You need a Service Account for each namespace this
# init container will be used in
apiVersion: v1
kind: ServiceAccount
metadata:
  name: deployment-checker
  namespace: <NAMESPACE_THAT_INIT_RUNS_IN>
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: deployment-checker
rules:
- apiGroups: ["apps", "extensions"]
  resources: ["deployments"]
  verbs: ["get"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: deployment-checker
# Subjects is a list
# You can use this to apply the same permissions
# To each Service Account you deploy
subjects:
- kind: ServiceAccount
  name: deployment-checker
  namespace: <NAMESPACE_THAT_INIT_RUNS_IN>
roleRef:
  kind: ClusterRole
  name: deployment-checker
  apiGroup: rbac.authorization.k8s.io

Now that we have done the prep work, we can add this init container to your deployment configuration:

spec:
  serviceAccount: deployment-checker
  serviceAccountName: deployment-checker
  initContainers:
    - name: deployment-check
      image: <CONTAINER_REGISTRY>/deployment-check:0.0.1
      imagePullPolicy: IfNotPresent
      args:
        - -deployment=<DEPLOYMENT_TO_WATCH>
        - -namespace=<NAMESPACE_OF_DEPLOYMENT_TO_WATCH>
  containers:
    - name: ...