Kubernetes Reliability Improvements

- Exclude kubelet CPU/RAM (kube-reserved) from cgroup. It decreases a
  chance of overcommitment
- Add a possibility to modify Kubelet node-status-update-frequency
- Add a posibility to configure node-monitor-grace-period,
  node-monitor-period, pod-eviction-timeout for Kubernetes controller
  manager
- Add Kubernetes Relaibility Documentation with recomendations for
  various scenarios.

Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>

roles/kubernetes/master/defaults/main.yml

@@ -18,6 +18,9 @@ kube_controller_memory_limit: 512M
 kube_controller_cpu_limit: 250m
 kube_controller_memory_requests: 170M
 kube_controller_cpu_requests: 100m
+kube_controller_node_monitor_grace_period: 40s
+kube_controller_node_monitor_period: 5s
+kube_controller_pod_eviction_timeout: 5m0s
 kube_scheduler_memory_limit: 512M
 kube_scheduler_cpu_limit: 250m
 kube_scheduler_memory_requests: 170M

roles/kubernetes/master/templates/manifests/kube-controller-manager.manifest.j2

@@ -28,6 +28,9 @@ spec:
     - --cluster-signing-cert-file={{ kube_cert_dir }}/ca.pem
     - --cluster-signing-key-file={{ kube_cert_dir }}/ca-key.pem
     - --enable-hostpath-provisioner={{ kube_hostpath_dynamic_provisioner }}
+    - --node-monitor-grace-period={{ kube_controller_node_monitor_grace_period }}
+    - --node-monitor-period={{ kube_controller_node_monitor_period }}
+    - --pod-eviction-timeout={{ kube_controller_pod_eviction_timeout }}
     - --v={{ kube_log_level }}
 {% if cloud_provider is defined and cloud_provider in ["openstack", "azure"] %}
     - --cloud-provider={{cloud_provider}}

roles/kubernetes/node/defaults/main.yml

@@ -12,6 +12,7 @@ kube_proxy_masquerade_all: true
 # Limits for kube components and nginx load balancer app
 kubelet_memory_limit: 512M
 kubelet_cpu_limit: 100m
+kubelet_status_update_frequency: 10s
 kube_proxy_memory_limit: 2000M
 kube_proxy_cpu_limit: 500m
 kube_proxy_memory_requests: 256M

roles/kubernetes/node/templates/kubelet.j2

@@ -9,7 +9,10 @@ KUBELET_ADDRESS="--address={{ ip | default("0.0.0.0") }}"
 KUBELET_HOSTNAME="--hostname-override={{ ansible_hostname }}"
 
 {# Base kubelet args #}
-{% set kubelet_args_base %}--pod-manifest-path={{ kube_manifest_dir }} --pod-infra-container-image={{ pod_infra_image_repo }}:{{ pod_infra_image_tag }}{% endset %}
+{% set kubelet_args_base %}--pod-manifest-path={{ kube_manifest_dir }} \
+--pod-infra-container-image={{ pod_infra_image_repo }}:{{ pod_infra_image_tag }} \
+--kube-reserved cpu={{ kubelet_cpu_limit }},memory={{ kubelet_memory_limit|regex_replace('Mi', 'M') }} \
+--node-status-update-frequency={{ kubelet_status_update_frequency }}{% endset %}
 
 {# DNS settings for kubelet #}
 {% if dns_mode == 'kubedns' %}