add host-based calculation for kube cpu/memory reserved resources

docs/operations/cgroups.md

@@ -70,4 +70,17 @@ After the setup, the cgroups hierarchy is as follows:
 └── ...
 ```
 
+## Automatic Resource Reservation Calculation
+
+While manually specifying resource reservations for kube and system daemons  works, Kubespray offers a more convenient approach. You can set the `kube_enable_auto_reserved_resources` flag to `true`. This instructs Kubespray to automatically calculate appropriate resource reservations for `kube_[master]_cpu_reserved` and `kube_[master]_memory_reserved` based on your host size. This eliminates the need for manual configuration, simplifying the process.
+
+When `kube_enable_auto_reserved_resources` is set to `true`, Kubespray calculates resource reservations as follows:
+
+CPU: 1% of the total CPU cores on the host machine + 80 millicores
+Memory: 5% of the total available system memory + 330 Megabytes
+
+This approach ensures that kubelet has sufficient resources to function properly while leaving the majority of resources available for your workloads.
+
+After the setup, the cgroups hierarchy remains the same as before.
+
 You can learn more in the [official kubernetes documentation](https://kubernetes.io/docs/tasks/administer-cluster/reserve-compute-resources/).

inventory/sample/group_vars/k8s_cluster/k8s-cluster.yml

@@ -264,6 +264,10 @@ default_kubelet_config_dir: "{{ kube_config_dir }}/dynamic_kubelet_dir"
 
 # Whether to run kubelet and container-engine daemons in a dedicated cgroup.
 # kube_reserved: false
+# If kube_enable_auto_reserved_resources is true,
+# the cpu and memory values are calculated based on the number of CPUs and memory size of the host.
+# The calculation formulas can be seen in https://github.com/kubernetes-sigs/kubespray/blob/master/docs/cgroups.md
+# kube_enable_auto_reserved_resources: false
 ## Uncomment to override default values
 ## The following two items need to be set when kube_reserved is true
 # kube_reserved_cgroups_for_service_slice: kube.slice

roles/kubernetes/node/defaults/main.yml

@@ -9,7 +9,7 @@ kubelet_bind_address: "{{ ip | default('0.0.0.0') }}"
 kube_resolv_conf: "/etc/resolv.conf"
 
 # Set to empty to avoid cgroup creation
-kubelet_enforce_node_allocatable: "\"\""
+kubelet_enforce_node_allocatable: '""'
 
 # Set runtime and kubelet cgroups when using systemd as cgroup driver (default)
 kube_service_cgroups: "{% if kube_reserved %}{{ kube_reserved_cgroups_for_service_slice }}{% else %}system.slice{% endif %}"
@@ -32,13 +32,14 @@ kube_node_addresses: >-
     {{ hostvars[host]['ip'] | default(fallback_ips[host]) }}{{ ' ' if not loop.last else '' }}
   {%- endfor -%}
 kubelet_secure_addresses: "localhost link-local {{ kube_pods_subnet }} {{ kube_node_addresses }}"
-
 # Reserve this space for kube resources
 # Whether to run kubelet and container-engine daemons in a dedicated cgroup. (Not required for resource reservations).
 kube_reserved: false
+kube_enable_auto_reserved_resources: false
+kube_reserved_cgroups_for_service_slice: kube.slice
 kube_reserved_cgroups: "/{{ kube_reserved_cgroups_for_service_slice }}"
-kube_memory_reserved: "256Mi"
-kube_cpu_reserved: "100m"
+kube_memory_reserved: "{{ kube_enable_auto_reserved_resources | ternary((ansible_memtotal_mb * 0.05 + 330) | int | string ~ 'Mi', '256Mi') }}"
+kube_cpu_reserved: "{{ kube_enable_auto_reserved_resources | ternary((ansible_processor_vcpus * 1000 * 0.01 + 80) | int | string ~ 'm', '100m') }}"
 kube_ephemeral_storage_reserved: "500Mi"
 kube_pid_reserved: "1000"
 
@@ -249,7 +250,6 @@ conntrack_modules:
   - nf_conntrack
   - nf_conntrack_ipv4
 
-
 ## Enable distributed tracing for kubelet
 kubelet_tracing: false
 kubelet_tracing_endpoint: 0.0.0.0:4317

roles/kubernetes/node/tasks/kubelet.yml

@@ -18,6 +18,15 @@
     - kubelet
     - kubeadm
 
+- name: Gather facts about the node
+  setup:
+    filter: ansible_memtotal_mb,ansible_processor_vcpus
+  tags:
+    - kubelet
+    - kubeadm
+  when:
+    - kube_enable_auto_reserved_resources
+
 - name: Write kubelet config file
   template:
     src: "kubelet-config.{{ kubeletConfig_api_version }}.yaml.j2"