<p>What is most simple way to start Kubernetes job with the http request (webhook)? I need to build docker image after push to github and have to do it inside cluster.</p>

<p>I think you are looking for <a href="https://www.knative.dev/docs/" rel="nofollow noreferrer">KNative</a>. Mainly the <a href="https://github.com/knative/build" rel="nofollow noreferrer">Build</a> part of it.</p>

<p>KNative is still on early stages, but is pretty much what you need. If the build features does not attend your needs, you can still use the other features like <a href="https://www.knative.dev/docs/serving/" rel="nofollow noreferrer">Serving</a> to trigger the container image from http calls and run the tools you need.</p>

<p>Here is the description from the Build Docs:</p>

<blockquote>
  <p>A <strong>Knative Build</strong> extends Kubernetes and utilizes existing Kubernetes
  primitives to provide you with the ability to run on-cluster container
  builds from source. For example, you can write a build that uses
  Kubernetes-native resources to obtain your source code from a
  repository, build a container image, then run that image.</p>
  
  <p>While Knative builds are optimized for building, testing, and
  deploying source code, you are still responsible for developing the
  corresponding components that:</p>
  
  <ul>
  <li>Retrieve source code from repositories.</li>
  <li>Run multiple sequential jobs against a shared filesystem, for example:
  
  <ul>
  <li>Install dependencies.</li>
  <li>Run unit and integration tests.</li>
  </ul></li>
  <li>Build container images.</li>
  <li>Push container images to an image registry, or deploy them to a cluster.</li>
  </ul>
  
  <p>The goal of a Knative build is to provide a standard, portable,
  reusable, and performance optimized method for defining and running
  on-cluster container image builds. By providing the “boring but
  difficult” task of running builds on Kubernetes, Knative saves you
  from having to independently develop and reproduce these common
  Kubernetes-based development processes.</p>
</blockquote>
