add image garbage collection (kubernetes-sigs#9832)

docs/vars.md

@@ -205,6 +205,15 @@ Stack](https://github.com/kubernetes-sigs/kubespray/blob/master/docs/dns-stack.m
 
 * *kubelet_streaming_connection_idle_timeout* - Set the maximum time a streaming connection can be idle before the connection is automatically closed.
 
+* *kubelet_image_gc_high_threshold* - Set the percent of disk usage after which image garbage collection is always run.
+  The percent is calculated by dividing this field value by 100, so this field must be between 0 and 100, inclusive.
+  When specified, the value must be greater than imageGCLowThresholdPercent. Default: 85
+
+* *kubelet_image_gc_low_threshold* - Set the percent of disk usage before which image garbage collection is never run.
+  Lowest disk usage to garbage collect to.
+  The percent is calculated by dividing this field value by 100, so the field value must be between 0 and 100, inclusive.
+  When specified, the value must be less than imageGCHighThresholdPercent. Default: 80
+
 * *kubelet_make_iptables_util_chains* - If `true`, causes the kubelet ensures a set of `iptables` rules are present on host.
 
 * *kubelet_systemd_hardening* - If `true`, provides kubelet systemd service with security features for isolation.

roles/kubernetes/node/templates/kubelet-config.v1beta1.yaml.j2

@@ -147,6 +147,12 @@ memorySwap:
 {% if kubelet_streaming_connection_idle_timeout is defined %}
 streamingConnectionIdleTimeout: {{ kubelet_streaming_connection_idle_timeout }}
 {% endif %}
+{% if kubelet_image_gc_high_threshold is defined %}
+imageGCHighThresholdPercent: {{ kubelet_image_gc_high_threshold }}
+{% endif %}
+{% if kubelet_image_gc_low_threshold is defined %}
+imageGCLowThresholdPercent: {{ kubelet_image_gc_low_threshold }}
+{% endif %}
 {% if kubelet_make_iptables_util_chains is defined %}
 makeIPTablesUtilChains: {{ kubelet_make_iptables_util_chains | bool }}
 {% endif %}