diff --git a/script/cache_critical_dns b/script/cache_critical_dns
new file mode 100755
index 0000000000..dedd453724
--- /dev/null
+++ b/script/cache_critical_dns
@@ -0,0 +1,180 @@
+#!/usr/bin/env ruby
+
+require 'resolv'
+require 'time'
+require 'timeout'
+require 'socket'
+
+HOSTS_PATH = "/etc/hosts"
+
+CRITICAL_HOST_ENV_VARS = %w{
+  DISCOURSE_DB_HOST
+  DISCOURSE_DB_BACKUP_HOST
+  DISCOURSE_REDIS_HOST
+  DISCOURSE_REDIS_SLAVE_HOST
+}
+
+def log(msg)
+  STDERR.puts "#{Time.now.iso8601}: #{msg}"
+end
+
+def error(msg)
+  log(msg)
+end
+
+def swap_address(hosts, name, ips)
+  new_file = []
+
+  hosts.split("\n").each do |line|
+    line = line.strip
+    if line[0] != '#'
+      _, hostname = line.strip.split(/\s+/)
+      next if hostname == name
+    end
+    new_file << line
+  end
+
+  ips.each do |ip|
+    new_file << "#{ip} #{name} # AUTO GENERATED: #{Time.now.iso8601}"
+  end
+
+  new_file.join("\n")
+end
+
+def hosts_entries(dns, name)
+  host = ENV[name]
+
+  results = dns.getresources(host, Resolv::DNS::Resource::IN::A)
+  results.concat dns.getresources(host, Resolv::DNS::Resource::IN::AAAA)
+
+  results.map do |result|
+    "#{result.address}"
+  end
+end
+
+def send_counter(name, description, labels, value)
+  host = "localhost"
+  port = 9405
+
+  if labels
+    labels = labels.map do |k, v|
+      "\"#{k}\": \"#{v}\""
+    end.join(",")
+  else
+    labels = ""
+  end
+
+  json = <<~JSON
+  {
+    "_type": "Custom",
+    "type": "Counter",
+    "name": "#{name}",
+    "description": "#{description}",
+    "labels": { #{labels} },
+    "value": #{value}
+  }
+  JSON
+
+  payload = +"POST /send-metrics HTTP/1.1\r\n"
+  payload << "Host: #{host}\r\n"
+  payload << "Connection: Close\r\n"
+  payload << "Content-Type: application/json\r\n"
+  payload << "Content-Length: #{json.bytesize}\r\n"
+  payload << "\r\n"
+  payload << json
+
+  socket = TCPSocket.new host, port
+  socket.write payload
+  socket.flush
+  result = socket.read
+  first_line = result.split("\n")[0]
+  if first_line.strip != "HTTP/1.1 200 OK"
+    error("Failed to report metric #{result}")
+  end
+  socket.close
+rescue => e
+  error("Failed to send metric to Prometheus #{e}")
+end
+
+def report_success
+  send_counter('critical_dns_successes_total', 'critical DNS resolution success', nil, 1)
+end
+
+def report_failure(errors)
+  errors.each do |host, count|
+    send_counter('critical_dns_failures_total', 'critical DNS resolution failures', host ? { host: host } : nil, count)
+  end
+end
+
+@vars = CRITICAL_HOST_ENV_VARS.map do |name|
+  begin
+    host = ENV[name]
+    next if !host || host.length == 0
+    IPAddr.new(ENV[name])
+    nil
+  rescue IPAddr::InvalidAddressError, IPAddr::AddressFamilyError
+    name
+  end
+end.compact
+
+def loop
+  errors = {}
+
+  Resolv::DNS.open do |dns|
+    dns.timeouts = 2
+
+    resolved = {}
+
+    hosts = @vars.each do |var|
+      host = ENV[var]
+
+      begin
+        entries = hosts_entries(dns, var)
+      rescue => e
+        error("Failed to resolve DNS for #{name} - #{e}")
+        errors[host] ||= 0
+        errors[host] += 1
+      end
+
+      if entries&.length > 0
+        resolved[host] = entries
+      else
+        error("Failed to find any DNS entry for #{var} : #{ENV[var]}")
+        errors[host] ||= 0
+        errors[host] += 1
+      end
+
+    end
+
+    hosts_content = File.read(HOSTS_PATH)
+    hosts = Resolv::Hosts.new(HOSTS_PATH)
+
+    changed = false
+    resolved.each do |name, ips|
+      if hosts.getaddresses(name).map(&:to_s).sort != ips.sort
+        log("IP addresses for #{name} changed to #{ips}")
+        hosts_content = swap_address(hosts_content, name, ips)
+        changed = true
+      end
+    end
+
+    if changed
+      File.write(HOSTS_PATH, hosts_content)
+    end
+
+  end
+rescue => e
+  error("Failed to access DNS - #{e}")
+  errors[nil] = 1
+ensure
+  if errors == {}
+    report_success
+  else
+    report_failure(errors)
+  end
+end
+
+while true
+  loop
+  sleep 30
+end