Scale down deployments if their ingress hasn't had any traffic - source: https://carlosbecker.com/posts/k8s-sandbox-costs/

pipe-down.sh

#!/bin/bash
# Source: https://carlosbecker.com/posts/k8s-sandbox-costs/
set -eo pipefail

ingress="$(kubectl get pods --output=jsonpath='{.items[*].metadata.name}' |
  xargs -n1 | grep "ingress-nginx" | head -n1)"

# cache all hosts that pass through the ingress
hosts="$(kubectl get ingress nginx-ingress --output=jsonpath='{.spec.rules[*].host}' | xargs -n1)"

# cache pods
pods="$(kubectl get pods)"

# cache ingress logs of the last 90min
logs="$(kubectl logs --since=90m "$ingress")"

# iterate over all deployments
kubectl get deployment --output=jsonpath='{.items[*].metadata.name}' |
  xargs -n1 |
  while read -r svc; do

    # skip svc that don't have pods running
    echo "$pods" | grep -q "$svc" || {
      echo "$svc: no pods running"
      continue
    }

    # skip svcs that don't pass through the ingress
    echo "$hosts" | grep -q "$svc" ||  {
      echo "$svc: not passing through ingress"
      continue
    }

    # skip svcs with pods running less than 1h
    echo "$pods" | grep "$svc" | awk '{print $5}' | grep -q h ||  {
      echo "$svc: pod running less than 1h"
      continue
    }

    # check if any traffic to that svc was made through the ingress in the
    # last hour, scale it down case none
    echo "$logs" | grep -q "default-$svc" || {
      echo "$svc: scaling down"
      kubectl scale deployments "$svc" --replicas 0 --record || true
    }
  done