Address hosts refresh timer feedback

Use OnUnitInactiveSec so the hosts setup service waits 10 seconds after each run completes before scheduling the next run. Add RandomizedDelaySec to de-synchronize nodes and reduce fleet-wide DNS bursts.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 2 people

parts/linux/cloud-init/artifacts/aks-localdns-hosts-setup.timer

@@ -4,10 +4,13 @@ Description=Run AKS LocalDNS hosts setup periodically
 [Timer]
 # Run immediately on boot
 OnBootSec=0
-# Refresh every 10 seconds. AKS critical FQDN IPs can change due to load balancer
-# rotation, Traffic Manager failover, or regional DNS updates. Frequent refreshes
-# keep stale IPs from causing the hosts plugin to serve unreachable addresses for long.
-OnUnitActiveSec=10s
+# Refresh 10 seconds after each run completes. AKS critical FQDN IPs can change
+# due to load balancer rotation, Traffic Manager failover, or regional DNS updates.
+# Frequent refreshes keep stale IPs from causing the hosts plugin to serve
+# unreachable addresses for long.
+OnUnitInactiveSec=10s
+# De-synchronize nodes so refreshes do not all hit DNS at the same time.
+RandomizedDelaySec=5s
 # Timer accuracy (how much systemd can delay)
 AccuracySec=1s