<p>I've read as much Kubernetes documentation as I can find, but I'm still having trouble understanding a specific scenario I have in mind.</p>

<p>For the sake of example, let's say I have a single node with 1GB of memory. I also have a deployment that wants 100 pods with memory limits set to 100MB and memory requests unset. The pods only use 1MB most of the time, but can sometimes jump up to 99MB.</p>

<p>Question 1: Will all 100 pods be scheduled onto the node?</p>

<p>Now, let's say all the pods simultaneously start using 99MB of memory each and stay there. There isn't enough memory on the machine to handle that, but none of the pods have exceeded their memory limit. I'm assuming Kubernetes evicts some pods at this point.</p>

<p>Question 2: When Kubernetes tries to reschedule the evicted pods, does it succeed since there is no memory request set? What happens when the node immediately runs out of memory again? Does this eviction, rescheduling keep happening over and over? If so, is there some metric that I can use to detect that this is happening?</p>

<p>A pod will be scheduled as long as there's an eligible node that can satisfy the requested resources. So if you do not specify request the pod will pretty much get scheduled. Request and limits are totally different things. Request is a condition for a pod to be scheduled and limit is a condition for a running pod already scheduled.</p>

<p>If you overcommit the actual resources on a node you will run into typical issues - if you overcommit on memory it'll start to swap and CPU there will just be general slow down. Either way the node and pods on it will become unresponsive. It's difficult to deal with and tools like request and limits set up sane boundaries that will help you not take things quite this far where you'll simply see the pod fail to schedule.</p>
