Pods dependecies init container

This container is used as an init container. It will check if at least one pod for each given label is running in the current namespace.

Prerequisites

For an optimal use of this init container, other pods must have readiness probe to doesn't allow routing from their services.

How to use it

The docker image is hosted on docker hub and can be found here: https://hub.docker.com/r/axelpereira/pods-dependencies-init-container

How it works

With a set of differents labels, this container will retrieve one pod per given labels which is in the Running phase. Then it will check if all containers inside these pods are ready. If a container is not ready, it's mean that a readiness probe is not fully ended successfully, so the init container will wait at least a new loop to end.

Settings

Environment Variable	Required	Default	Description
POD_LABELS	Yes	-	This is comma (,) seperated string for labels of dependency pods which will be check of Running phase. If you want multiple label to check you must seperate with a semicolon (;).
MAX_RETRY	NO	5	Maximum number of times for which init container will try to check if any pod with give POD_LABELS is Running.
RETRY_TIME_OUT	NO	1500	Number of milliseconds init container will time out between each retry.
INITIAL_DELAY	NO	1500	Number of milliseconds init container will time out before launch the first check.

Example usage:

spec:
  containers:
  ...
  serviceAccountName: {{ .Values.serviceAccount }} #optional
  initContainers:
  - name: pod-dependency
    image: axelpereira/pods-dependencies-init-container:1.0
    env:
    - name: POD_LABELS
      value: app=nodeapp,name=mongo-1;app=javaapp,name=billing-1
    - name: MAX_RETRY
      value: "10"
    - name: RETRY_TIME_OUT
      value: "5000"
    - name: INITIAL_DELAY
      value: "30"
    - name: KUBE_NAMESPACE
      valueFrom:
        fieldRef:
          fieldPath: metadata.namespace```

## RBAC
In case of RBAC this container requires `pods` resource `get`, `list`, `watch` access. Which can be provided by below yaml
```yaml
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: {{ .Values.serviceAccount }}
rules:
  - apiGroups:
      - ""
    resources:
      - pods
      - services
      - endpoints
    verbs:
      - get
      - list
      - watch
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: {{ .Values.serviceAccount }}
  namespace: {{ .Values.namespace }}
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: system:serviceaccount:{{ .Values.serviceAccount }}:default
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: {{ .Values.serviceAccount }}
subjects:
- kind: ServiceAccount
  name: {{ .Values.serviceAccount }}
  namespace: {{ .Values.namespace }}