This change appends the full hostname to the mirror pod name (instead of taking
the first token) so that if the hostname is overriden, we'd not be creating
unncessary name conflicts. An example would be that a user overrides the
hostnames to be "127.0.0.1" and "127.0.0.2", and both of them were resolved to
"127" for the mirror pod name suffix.
Also, because `uname -n` could return a FQDN or not, this change takes only
the first token of it as the hostname for consistency.
If a static pod changes, delete the corresponding mirror pod. When kubelet
could not see mirror pod from the API server update, it'd attemp to create a
new mirror pod with up-to-date specs.
Currently, API server is not aware of the static pods (manifests from
sources other than the API server, e.g. file and http) at all. This is
inconvenient since users cannot check the static pods through kubectl.
It is also sub-optimal because scheduler is unaware of the resource
consumption by these static pods on the node.
This change syncs the information back to the API server by creating a
mirror pod via API server for each static pod.
- Kubelet creates containers for the static pod, as it would do
normally.
- If a mirror pod gets deleted, Kubelet will re-create one. The
containers are sync'd to the static pods, so they will not be
affected.
- If a static pod gets removed from the source (e.g. manifest file
removed from the directory), the orphaned mirror pod will be deleted.
Note that because events are associated with UID, and the mirror pod has
a different UID than the original static pod, the events will not be
shown for the mirror pod when running `kubectl describe pod
<mirror_pod>`.
Hostname behavior across operating systems is inconsistent (Macs can
have uppercase host names, so can some other systems). In general,
always strings.ToLower(os.Hostname()).
There are two main goals for this change.
1. Fix the naming scheme in kubelet so that it accepts DNS subdomain
name/namespaces correctly (#4920). The design is discussed in #3453.
2. Prepare for syncing the static pods back to the apiserver(#4090). This
includes
- Eliminate the source component in the internal full pod name (#4922). Pods
no longer need sources as they will all be sync'd via apiserver.
- Changing the naming scheme for the static (file-, http-, and etcd-based)
pods such that they are distinguishable when syncing back to the apiserver.
The changes includes:
* name = <pod.Name>-<hostname>
* namespace = <cluster_namespace> (i.e. "default" for now).
* container_name = k8s_<contianer_name>.<hash_of_container>_<pod_name>_<namespace>_<uid>_<random>
Note that this is not backward-compatible, meaning the kubelet won't recognize
existing running containers using the old naming scheme.
Yu-Ju Hong