Kubevirt: Run Descheduler on node boot to rebalance cluster apps

Update_RunDeschedulerOnBoot will run the descheduler to
evict pods from the edge node on boot.
This is to allow rebalancing apps via re-scheduling them
with an aim to meet affinity as specified in the pod config.

This path includes a series of gates to ensure the destination
node is available as a scheduling destination.
- Wait for the kubernetes api to be available.
- Wait until node is online and uncordoned.

Signed-off-by: Andrew Durbin <[email protected]>

Author: andrewd-zededa

pkg/kube/cluster-init.sh

@@ -862,6 +862,7 @@ fi
         check_kubeconfig_yaml_files
         check_and_remove_excessive_k3s_logs
         check_and_run_vnc
+        Update_RunDeschedulerOnBoot
         wait_for_item "wait"
         sleep 15
 done

pkg/kube/cluster-update.sh

@@ -3,6 +3,61 @@
 # Copyright (c) 2024 Zededa, Inc.
 # SPDX-License-Identifier: Apache-2.0
 
+EdgeNodeInfoPath="/persist/status/zedagent/EdgeNodeInfo/global.json"
+COMP_UPDATE_PATH="/usr/bin/update-component"
+
 link_multus_into_k3s() {
     ln -s /var/lib/cni/bin/multus /var/lib/rancher/k3s/data/current/bin/multus
 }
+
+# Update_RunDeschedulerOnBoot will run the descheduler to evict pods from the edge node
+# on boot. This is to allow rebalancing apps via re-scheduling them to requested node
+# affinity as specified in the pod config.
+Update_RunDeschedulerOnBoot() {
+    # Currently only run once per boot
+    if [ -f /tmp/descheduler-ran-onboot ]; then
+        return
+    fi
+
+    if [ ! -f $EdgeNodeInfoPath ]; then
+        return
+    fi
+    # is api ready
+    if ! update_isClusterReady; then
+        return
+    fi
+    # Don't run unless it has been installed
+    if [ ! descheduler_install ]; then
+        return
+    fi
+    # node ready and allowing scheduling
+    node=$(jq -r '.DeviceName' < $EdgeNodeInfoPath | tr -d '\n' | tr '[:upper:]' '[:lower:]')
+    node_count_ready=$(kubectl get "node/${node}" | grep -v SchedulingDisabled | grep -cw Ready )
+    if [ "$node_count_ready" -ne 1 ]; then
+        return
+    fi
+    # Job lives persistently in cluster, cleanup after old runs
+    if kubectl -n kube-system get job/descheduler-job; then
+        kubectl -n kube-system delete job/descheduler-job
+    fi
+    kubectl apply -f /etc/descheduler-job.yaml
+    touch /tmp/descheduler-ran-onboot
+}
+
+update_isClusterReady() {
+    if ! kubectl cluster-info; then
+        return 1
+    fi
+
+    if ! update_Helper_APIResponding; then
+        return 1
+    fi
+    return 0
+}
+
+update_Helper_APIResponding() {
+    if $COMP_UPDATE_PATH --check-api-ready; then
+        return 0
+    fi
+    return 1
+}