Revert "Add HOSTNAME to env by default for pod containers"

[Random-Liu]

This reverts commit 4c3e195.

See reason: #895 (comment)

Signed-off-by: Lantao Liu [email protected]

[yujuhong]

/lgtm

[yujuhong]

From the kube-addon-manager log:

INFO: Leader is bootstrap-e2e-master
INFO: Not elected leader, going back to sleep.
INFO: Leader is bootstrap-e2e-master
INFO: Not elected leader, going back to sleep.
INFO: Leader is bootstrap-e2e-master
INFO: Not elected leader, going back to sleep.
INFO: Leader is bootstrap-e2e-master

The addon manager did not think it's the leader bootstrap-e2e-master and refused to continue creating all the addons (including the cluster roles):
https://github.com/kubernetes/kubernetes/blob/d0439d417b0563d44c65b6e400e2070964dea7d1/cluster/addons/addon-manager/kube-addons.sh#L162-L164

[yujuhong]

By the way, kube-addon-manager runs in the host network

[yujuhong]

By the way, kube-addon-manager runs in the host network

kubelet probably doesn't set hostname for pods running in the host network. Not sure how docker handles this.

[estesp]

Interesting; it definitely looks like HOSTNAME is part of the problem here.

This is the code where Docker engine sets up HOSTNAME as a default env var in every container (https://github.com/moby/moby/blob/master/container/container.go#L694-L718), which is called from the OCI spec generator without any kind of checking if netns == host.

I also looked at dockershim and don't see any env replacement or changes happening; I can't even find the string "HOSTNAME" in any files in pkg/kubelet. So, something is definitely different, but I'm not sure what is occurring here.

[estesp]

hmm, looks like the missing piece is that by the time that code runs in Docker, if --net=host it has set the metadata config's hostname to the actual host hostname; not sure if that is the case with the way this is happened here; Docker for Mac example:

docker run --rm --net=host alpine sh -c 'echo $HOSTNAME'
linuxkit-025000000001

The container's hostname is the LinuxKit VM hostname.

[yujuhong]

I also looked at dockershim and don't see any env replacement or changes happening; I can't even find the string "HOSTNAME" in any files in pkg/kubelet. So, something is definitely different, but I'm not sure what is occurring here.

Kubelet passes the hostname through the podsandbox config, but it doesn't add an env variable directly.

hmm, looks like the missing piece is that by the time that code runs in Docker, if --net=host it has set the metadata config's hostname to the actual host hostname

That sounds reasonable. Docker probably derives this information before passing it through the config.

[Random-Liu]

https://github.com/moby/moby/blob/master/daemon/container_operations.go#L936-L943

I'll make the change. And we may want to define the behavior in CRI.