How to run command after initialization

Question

I would like to run specific command after initialization of deployment is successful.

This is my yaml file:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: auth
spec:
  replicas: 1
  template:
    metadata:
        labels:
          app: auth
    spec:
      containers:
        - name: auth
          image: {{my-service-image}}
          env:
          - name: NODE_ENV
            value: "docker-dev"
          resources:
            requests:
              cpu: 100m
              memory: 100Mi
          ports:
            - containerPort: 3000

However, I would like to run command for db migration after (not before) deployment is successfully initialized and pods are running.

I can do it manually for every pod (with kubectl exec), but this is not very scalable.

shkaper · Accepted Answer · 2019-08-19 08:14:52Z

160

I resolved it using lifecycles:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: auth
spec:
  replicas: 1
  template:
    metadata:
        labels:
          app: auth
    spec:
      containers:
        - name: auth
          image: {{my-service-image}}
          env:
          - name: NODE_ENV
            value: "docker-dev"
          resources:
            requests:
              cpu: 100m
              memory: 100Mi
          ports:
            - containerPort: 3000
          lifecycle:
            postStart:
              exec:
                command: ["/bin/sh", "-c", {{cmd}}]

edited Aug 19, 2019 at 8:14

shkaper

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answered May 23, 2017 at 22:58

meerkat

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10 Comments

Rhubarb Over a year ago

great answer for something that works in a command line and in the same container, but I would like to do this in a separate container that runs to completion and goes away like an init-container

Denis V Over a year ago

@Rhubarb Personally I solved it creating a special management Pod, in which I run all the commands before deploying the app itself.

SeB.Fr Over a year ago

be careful cause according tho the documentation, there is not garantee that the postStart is called after or before the container entry point is called.

yuranos Over a year ago

Yes, but since entrypoint and postStart are allegedly running asynchronously, you can add a sleep command as a last resort.

Mohammed Noureldin Over a year ago

IMPORTANT NOTE: this will not wait until the pod is ready, but rather will execute immediately after the pod starts.

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Tomek · Accepted Answer · 2020-11-05 09:12:22Z

19

You can use Helm to deploy a set of Kubernetes resources. And then, use a Helm hook, e.g. post-install or post-upgrade, to run a Job in a separate docker container. Set your Job to invoke db migration. A Job will run >=1 Pods to completion, so it fits here quite well.

edited Nov 5, 2020 at 9:12

Tomek

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answered Mar 13, 2018 at 20:06

Ava

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Comments

D.Fitz · Accepted Answer · 2025-04-15 02:24:04Z

4

My solution uses a readinessProbe
The application needs additional input that's only available after the process has fully initialized and the postStart method was executing before the app is ready.

readinessProbe:
  exec:
    command: [healthcheck]
  initialDelaySeconds: 30
  periodSeconds: 2
  timeoutSeconds: 1
  successThreshold: 3
  failureThreshold: 10

WARNING: This method could cause undefined behavior. Take care with how you use it.

edited Apr 15 at 2:24

answered May 21, 2021 at 14:41

D.Fitz

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8 Comments

Shadman Over a year ago

As per my understanding this will execute this command time to time not only once

D.Fitz Over a year ago

Check the link I provided. I think you are referring to a liveness probe.

Máxima Alekz Over a year ago

@D.Fitz so using this config, when app is ready will run "healthcheck"? What is exactly healthcheck, an script? Must be bash? can be something like Python/Node/PHP?

D.Fitz Over a year ago

@MáximaAlekz the command will execute inside the container. You can use any command the container is equipped to handle.

Mohammed Noureldin Over a year ago

The role of readiness and lifeness prob is not to execute commands that have side effects. They are here just to do what their names say. Check the health of the pod.

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