Move pods into "kubepods" cgroup.

Previously with docker runtime they would be in /sys/fs/cgroups/*/docker/ (or
even /sys/fs/cgroups/*/podruntime/docker/) and with cri-containerd in
/sys/fs/cgroups/*/k8s.io/.

If using --cgroups-per-qos then a slightly different --cgroup-root is required,
leave a comment.

Signed-off-by: Ian Campbell <ijc@docker.com>

Author: Ian Campbell

pkg/kubelet/build.yml

@@ -29,6 +29,7 @@ config:
     cgroups:
     - systemreserved
     - podruntime
+    - kubepods
     mkdir:
     - /var/lib/kubeadm
     - /var/lib/cni/conf

pkg/kubelet/kubelet.sh

@@ -63,6 +63,14 @@ echo "kubelet.sh: ${await} has arrived" 2>&1
 
 mkdir -p /etc/kubernetes/manifests
 
+# If using --cgroups-per-qos then need to use --cgroup-root=/ and not
+# the --cgroup-root=kubepods from below. This can be done at image
+# build time by adding to the service definition:
+#
+#    command:
+#      - /usr/bin/kubelet.sh
+#      - --cgroup-root=/
+#      - --cgroups-per-qos
 exec kubelet --kubeconfig=/etc/kubernetes/kubelet.conf \
 	      --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf \
 	      --pod-manifest-path=/etc/kubernetes/manifests \
@@ -77,4 +85,5 @@ exec kubelet --kubeconfig=/etc/kubernetes/kubelet.conf \
 	      --cadvisor-port=0 \
 	      --kube-reserved-cgroup=podruntime \
 	      --system-reserved-cgroup=systemreserved \
+	      --cgroup-root=kubepods \
 	      $KUBELET_ARGS $@