Update your Vultr firewall rules to only accept your IP address as incoming SSH

vultr-firewall-updater.sh

#!/usr/bin/env bash
#
# Automatically updates the IP addresses for the ingress rules for SSH access
# at my home proxy instance on Vultr
#
# Requires: jq, curl, dig

config() {
  # Define your Vultr API Key
  export VULTR_API_KEY=YOUR-VULTR-API-KEY

  # Get the current external IP addresses
  current_ip1=$(command-to-get-ip-1) # dig +short ip-1.yourdomain.com
  current_ip2=$(command-to-get-ip-1) # dig +short ip-2.yourdomain.com
  current_ips=$(echo "[\"${current_ip1}\",\"${current_ip2}\"]" | jq 'sort')
}

main() {
  config

  # Get existing rules at the Vultr firewall
  firewall_id=$(get_firewalls)
  rules=$(get_rules_by_firewall_id "$firewall_id")
  firewall_ips=$(echo "$rules" | jq -r "[.[].subnet] | sort")

  # If existing firewall whitelisted IPs are the same as current IPs, do nothing
  test "$firewall_ips" = "$current_ips" && return

  log "Updating firewall rules"
  for id in $(echo "$rules" | jq -r ".[].id"); do
    log "Deleting firewall rule ID ${id}"
    call DELETE "firewalls/${firewall_id}/rules/${id}"
  done

  log "Creating new rules"
  call POST "firewalls/${firewall_id}/rules" "$(rule_create_payload "$current_ip1")" > /dev/null
  call POST "firewalls/${firewall_id}/rules" "$(rule_create_payload "$current_ip2")" > /dev/null
}

rule_create_payload() {
  ip=$1

  echo "{
    \"ip_type\":\"v4\",
    \"protocol\": \"tcp\",
    \"port\": 22,
    \"subnet_size\": 32,
    \"notes\": \"[AUTO] Home network external IP\",
    \"subnet\": \"${ip}\"
  }"
}

log() {
  msg=$1
  date=$(date -u +'%Y-%m-%dT%H:%M:%S.%3NZ')

  echo "[$date] $msg"
}

get_firewalls() {
  call GET firewalls | jq -r '.firewall_groups[] | select(.description == "Home proxy") .id'
}

get_rules_by_firewall_id() {
  local firewall_id=$1
  call GET "firewalls/${firewall_id}/rules" | jq -r '[.firewall_rules[] | select(.notes | contains("[AUTO]"))]'
}

call() {
  local method=$1
  local url=$2
  local params=$3

  curl "https://api.vultr.com/v2/${url}" -X "${method}" \
    -H "Content-Type: application/json" \
    -H "Authorization: Bearer ${VULTR_API_KEY}" \
    --data "$params"
}

main