start-vm-caddy.sh

#!/bin/sh

name=$1

if [[ -z "$name" ]]; then
  echo "missing domain name argument"
  exit 1
fi

CADDYFILE=${CADDYFILE:-/etc/caddy/Caddyfile}

if [[ -z "$(which jq)" ]]; then
  missingpkgs="$missingpkgs jq"
fi

if [[ -z "$(which curl)" ]]; then
  missingpkgs="$missingpkgs curl"
fi

if [[ -n "$missingpkgs" ]]; then
  apk add $missingpkgs
fi

mkdir -p "$(dirname "$CADDYFILE")"

function get_ips {
  curl -s -H "accept: application/dns-json" "https://1.1.1.1/dns-query?name=$name&type=a" | jq -r '.Answer | .[] | .data + " " + (.TTL | tostring)'
}

(
  while [[ -f "/proc/$$/status" ]]; do
    ips_and_ttls="$(get_ips)"
    current_ips="$(printf "$ips_and_ttls" | awk '{ print $1 }')"
    ttl="$(printf "$ips_and_ttls" | awk '{ print $2 }' | sort -rn | head -n1)"

    if [[ "$prev_ips" != "$current_ips" ]]; then
      cat <<EOF > "$CADDYFILE"
http://:8428 {
	reverse_proxy /insert/* $(printf "$current_ips" | awk '{ print "http://" $1 ":8480" }' | tr '\n' ' ' | xargs) {
		health_uri /metrics
	}
	reverse_proxy /select/* $(printf "$current_ips" | awk '{ print "http://" $1 ":8481" }' | tr '\n' ' ' | xargs) {
		health_uri /metrics
	}
}
EOF
    fi

    prev_ips="$current_ips"
    sleep $((ttl + 5))
  done
) &

while [[ ! -f "$CADDYFILE" ]]; do
  sleep 1
done

exec caddy run -w -c "$CADDYFILE"