When a pod is created but no resource limit is specified, which component is responsible to calculate or assign resource limit to that pod? Is that the kubelet or the Docker?
If a pod doesn't specify any resource limits, it's ultimately up to the Linux kernel scheduler on the node to assign CPU cycles or not to the process, and to OOM-kill either the pod or other processes on the node if memory use is excessive. Neither Kubernetes nor Docker will assign or guess at any sort of limits.
So if you have a process with a massive memory leak, and it gets scheduled on a very large but quiet instance with 256 GB of available memory, it will get to use almost all of that memory before it gets OOM-killed. If a second replica gets scheduled on a much smaller instance with only 4 GB, it's liable to fail much sooner. Usually you'll want to actually set limits for consistent behavior.