<p>I'm following this task <a href="https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes" rel="nofollow noreferrer">Configure Liveness, Readiness and Startup Probes</a> 
and it's unclear to me whether a container where the check is made is a container only used to check the availability of a pod? Because it makes sense if pod check container fails therefore api won't let any traffic in to the pod.</p>

<p>So a health check signal must be coming from container where some image or app runs? (<em>sorry, another question</em>)</p>

<p>From the link you provided it seems like they are speaking about <strong>Containers</strong> and not <strong>Pods</strong> so the probes are meant to be per containers. When all containers are ready the pod is described as ready too as written in the doc you provided : </p>

<blockquote>
  <p>The kubelet uses readiness probes to know when a Container is ready to
  start accepting traffic. A Pod is considered ready when all of its
  Containers are ready. One use of this signal is to control which Pods
  are used as backends for Services. When a Pod is not ready, it is
  removed from Service load balancers.</p>
</blockquote>

<p>So yes, every containers that are running some images or apps are supposed to expose those metrics.</p>
