kubernetes-ingress: A rollout restart, or scale down of haproxy causes 503 connection timeout errors

I’m using helm to run HaProxy ingress with autoscaling enabled (chart version 1.21.1). Whenever an HaProxy pod terminates (because of a scale down event, or a rollout restart), I start seeing 503 backend connection timeout errors for a few seconds.

I tried adding the following example config for graceful shutdown, but that did not resolve the issue:

## Example preStop for graceful shutdown
lifecycle: {}
    preStop:
      exec:
        command: ["/bin/sh", "-c", "kill -USR1 $(pidof haproxy); while killall -0 haproxy; do sleep 1; done"]