diff --git a/lib/good_job.rb b/lib/good_job.rb
index c880338cb..fa76f8061 100644
--- a/lib/good_job.rb
+++ b/lib/good_job.rb
@@ -32,8 +32,8 @@
 require "good_job/notifier"
 require "good_job/poller"
 require "good_job/probe_server"
-require "good_job/middleware/catch_all"
-require "good_job/middleware/healthcheck"
+require "good_job/probe_server/middleware/catchall"
+require "good_job/probe_server/middleware/healthcheck"
 require "good_job/http_server"
 require "good_job/scheduler"
 require "good_job/shared_executor"
diff --git a/lib/good_job/cli.rb b/lib/good_job/cli.rb
index c51690b5f..9d2c8dd06 100644
--- a/lib/good_job/cli.rb
+++ b/lib/good_job/cli.rb
@@ -104,10 +104,8 @@ def start
       capsule.start
       systemd.start
 
-      middleware = Rails.application.config.good_job.middleware
-      port = Rails.application.config.good_job.middleware_port
-      if middleware && port
-        probe_server = GoodJob::ProbeServer.new(app: middleware, port: port)
+      if configuration.probe_port
+        probe_server = GoodJob::ProbeServer.new(app: configuration.probe_server_app, port: configuration.probe_port)
         probe_server.start
       end
 
diff --git a/lib/good_job/configuration.rb b/lib/good_job/configuration.rb
index dcef0d706..eabf7ed69 100644
--- a/lib/good_job/configuration.rb
+++ b/lib/good_job/configuration.rb
@@ -338,6 +338,12 @@ def probe_port
         env['GOOD_JOB_PROBE_PORT']
     end
 
+    # Rack compliant application to be run on the ProbeServer
+    # @return [nil, Class]
+    def probe_server_app
+      rails_config[:probe_server_app]
+    end
+
     def enable_listen_notify
       return options[:enable_listen_notify] unless options[:enable_listen_notify].nil?
       return rails_config[:enable_listen_notify] unless rails_config[:enable_listen_notify].nil?
diff --git a/lib/good_job/middleware/catch_all.rb b/lib/good_job/middleware/catch_all.rb
deleted file mode 100644
index 54e41035e..000000000
--- a/lib/good_job/middleware/catch_all.rb
+++ /dev/null
@@ -1,9 +0,0 @@
-module GoodJob
-  module Middleware
-    class CatchAll
-      def self.call(env)
-        [404, {}, ["Not found"]]
-      end
-    end
-  end
-end
diff --git a/lib/good_job/middleware/healthcheck.rb b/lib/good_job/middleware/healthcheck.rb
deleted file mode 100644
index 381ad7335..000000000
--- a/lib/good_job/middleware/healthcheck.rb
+++ /dev/null
@@ -1,25 +0,0 @@
-module GoodJob
-  module Middleware
-    class Healthcheck
-      def initialize(app)
-        @app = app
-      end
-
-      def call(env)
-        case Rack::Request.new(env).path
-        when '/', '/status'
-          [200, {}, ["OK"]]
-        when '/status/started'
-          started = GoodJob::Scheduler.instances.any? && GoodJob::Scheduler.instances.all?(&:running?)
-          started ? [200, {}, ["Started"]] : [503, {}, ["Not started"]]
-        when '/status/connected'
-          connected = GoodJob::Scheduler.instances.any? && GoodJob::Scheduler.instances.all?(&:running?) &&
-                      GoodJob::Notifier.instances.any? && GoodJob::Notifier.instances.all?(&:connected?)
-          connected ? [200, {}, ["Connected"]] : [503, {}, ["Not connected"]]
-        else
-          @app.call(env)
-        end
-      end
-    end
-  end
-end
diff --git a/lib/good_job/probe_server.rb b/lib/good_job/probe_server.rb
index 4c350c4b1..f43c0501c 100644
--- a/lib/good_job/probe_server.rb
+++ b/lib/good_job/probe_server.rb
@@ -8,7 +8,7 @@ def self.task_observer(time, output, thread_error) # rubocop:disable Lint/Unused
       GoodJob._on_thread_error(thread_error) if thread_error
     end
 
-    def initialize(app:, port:)
+    def initialize(port:, app: default_probe_server)
       @port = port
       @app = app
     end
@@ -28,5 +28,14 @@ def stop
       @handler&.stop
       @future&.value # wait for Future to exit
     end
+
+    private
+
+    def default_probe_server
+      Rack::Builder.new do
+        use Middleware::Healthcheck
+        run Middleware::Catchall.new
+      end
+    end
   end
 end
diff --git a/lib/good_job/probe_server/middleware/catchall.rb b/lib/good_job/probe_server/middleware/catchall.rb
new file mode 100644
index 000000000..19465faac
--- /dev/null
+++ b/lib/good_job/probe_server/middleware/catchall.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module GoodJob
+  class ProbeServer
+    module Middleware
+      class Catchall
+        def call(_)
+          [404, {}, ["Not found"]]
+        end
+      end
+    end
+  end
+end
diff --git a/lib/good_job/probe_server/middleware/healthcheck.rb b/lib/good_job/probe_server/middleware/healthcheck.rb
new file mode 100644
index 000000000..906d7d1f0
--- /dev/null
+++ b/lib/good_job/probe_server/middleware/healthcheck.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module GoodJob
+  class ProbeServer
+    module Middleware
+      class Healthcheck
+        def initialize(app)
+          @app = app
+        end
+
+        def call(env)
+          case Rack::Request.new(env).path
+          when '/', '/status'
+            [200, {}, ["OK"]]
+          when '/status/started'
+            started = GoodJob::Scheduler.instances.any? && GoodJob::Scheduler.instances.all?(&:running?)
+            started ? [200, {}, ["Started"]] : [503, {}, ["Not started"]]
+          when '/status/connected'
+            connected = GoodJob::Scheduler.instances.any? && GoodJob::Scheduler.instances.all?(&:running?) &&
+                        GoodJob::Notifier.instances.any? && GoodJob::Notifier.instances.all?(&:connected?)
+            connected ? [200, {}, ["Connected"]] : [503, {}, ["Not connected"]]
+          else
+            @app.call(env)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/good_job/cli_spec.rb b/spec/lib/good_job/cli_spec.rb
index 059a1ebbc..ba13f736d 100644
--- a/spec/lib/good_job/cli_spec.rb
+++ b/spec/lib/good_job/cli_spec.rb
@@ -56,13 +56,47 @@
         allow(GoodJob::ProbeServer).to receive(:new).and_return probe_server
       end
 
-      it 'starts a ProbeServer' do
-        cli = described_class.new([], { probe_port: 3838 }, {})
-        cli.start
+      context 'when a port is specified' do
+        it 'starts a ProbeServer with the specified port and a "nil" app' do
+          cli = described_class.new([], { probe_port: 3838 }, {})
+          cli.start
+
+          expect(GoodJob::ProbeServer).to have_received(:new).with(app: nil, port: 3838)
+          expect(probe_server).to have_received(:start)
+          expect(probe_server).to have_received(:stop)
+        end
+      end
+
+      context 'when a port is and an app is set in the Rails configuration' do
+        it 'starts a ProbesServer with the configured port and app' do
+          app_mock = instance_double(Proc, call: nil)
+          configuration_mock = instance_double(
+            GoodJob::Configuration,
+            probe_server_app: app_mock, 
+            probe_port: 3838,
+            options: {},
+            daemonize?: false,
+            shutdown_timeout: 100,
+          )
+          allow(GoodJob).to receive_messages(configuration: configuration_mock)
+          cli = described_class.new([], [], {})
+          cli.start
+
+          expect(GoodJob::ProbeServer).to have_received(:new).with(app: app_mock, port: 3838)
+          expect(probe_server).to have_received(:start)
+          expect(probe_server).to have_received(:stop)
+        end
+      end
+
+      context 'when a port is not specified' do
+        it 'does not start a ProbeServer' do
+          cli = described_class.new([], {}, {})
+          cli.start
 
-        expect(GoodJob::ProbeServer).to have_received(:new).with(port: 3838)
-        expect(probe_server).to have_received(:start)
-        expect(probe_server).to have_received(:stop)
+          expect(GoodJob::ProbeServer).not_to have_received(:new)
+          expect(probe_server).not_to have_received(:start)
+          expect(probe_server).not_to have_received(:stop)
+        end
       end
     end
 
diff --git a/spec/lib/good_job/probe_server/middleware/catchall_spec.rb b/spec/lib/good_job/probe_server/middleware/catchall_spec.rb
new file mode 100644
index 000000000..410c0e8d4
--- /dev/null
+++ b/spec/lib/good_job/probe_server/middleware/catchall_spec.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe GoodJob::ProbeServer::Middleware::Catchall do
+  describe '#call' do
+    it 'returns "Not Found"' do
+      response = described_class.new.call("")
+      expect(response[0]).to eq(404)
+    end
+  end
+end
diff --git a/spec/lib/good_job/middleware/healthcheck_spec.rb b/spec/lib/good_job/probe_server/middleware/healthcheck_spec.rb
similarity index 73%
rename from spec/lib/good_job/middleware/healthcheck_spec.rb
rename to spec/lib/good_job/probe_server/middleware/healthcheck_spec.rb
index 14a7474f9..3dfa74374 100644
--- a/spec/lib/good_job/middleware/healthcheck_spec.rb
+++ b/spec/lib/good_job/probe_server/middleware/healthcheck_spec.rb
@@ -3,13 +3,9 @@
 require 'rails_helper'
 require 'net/http'
 
-RSpec.describe GoodJob::ProbeServer do
-  let(:healthcheck_rack_app) do
-    Rack::Builder.app do
-      use GoodJob::Middleware::Healthcheck
-      run GoodJob::Middleware::CatchAll
-    end
-  end
+RSpec.describe GoodJob::ProbeServer::Middleware::Healthcheck do
+  let(:app) { instance_double(Proc, call: nil) }
+  let(:healthcheck_middleware) { described_class.new(app) }
   let(:port) { 3434 }
 
   describe '#call' do
@@ -20,7 +16,7 @@
       let(:path) { '/' }
 
       it 'returns "OK"' do
-        response = healthcheck_rack_app.call(env)
+        response = healthcheck_middleware.call(env)
         expect(response[0]).to eq(200)
       end
     end
@@ -30,7 +26,7 @@
 
       context 'when there are no running schedulers' do
         it 'returns 503' do
-          response = healthcheck_rack_app.call(env)
+          response = healthcheck_middleware.call(env)
           expect(response[0]).to eq(503)
         end
       end
@@ -40,7 +36,7 @@
           scheduler = instance_double(GoodJob::Scheduler, running?: true, shutdown: true, shutdown?: true)
           GoodJob::Scheduler.instances << scheduler
 
-          response = healthcheck_rack_app.call(env)
+          response = healthcheck_middleware.call(env)
           expect(response[0]).to eq(200)
         end
       end
@@ -51,7 +47,7 @@
 
       context 'when there are no running schedulers or notifiers' do
         it 'returns 503' do
-          response = healthcheck_rack_app.call(env)
+          response = healthcheck_middleware.call(env)
           expect(response[0]).to eq(503)
         end
       end
@@ -64,7 +60,7 @@
           notifier = instance_double(GoodJob::Notifier, connected?: false, shutdown: true, shutdown?: true)
           GoodJob::Notifier.instances << notifier
 
-          response = healthcheck_rack_app.call(env)
+          response = healthcheck_middleware.call(env)
           expect(response[0]).to eq(503)
         end
       end
@@ -77,10 +73,19 @@
           notifier = instance_double(GoodJob::Notifier, connected?: true, shutdown: true, shutdown?: true)
           GoodJob::Notifier.instances << notifier
 
-          response = healthcheck_rack_app.call(env)
+          response = healthcheck_middleware.call(env)
           expect(response[0]).to eq(200)
         end
       end
     end
+
+    describe 'forwarding unknown requests to given app' do
+      let(:path) { '/unhandled_path' }
+
+      it 'passes the request to the given app' do
+        healthcheck_middleware.call(env)
+        expect(app).to have_received(:call).with(env)
+      end
+    end
   end
 end
diff --git a/spec/lib/good_job/probe_server_spec.rb b/spec/lib/good_job/probe_server_spec.rb
index cd35ccaa1..8b35913e7 100644
--- a/spec/lib/good_job/probe_server_spec.rb
+++ b/spec/lib/good_job/probe_server_spec.rb
@@ -4,42 +4,61 @@
 require 'net/http'
 
 RSpec.describe GoodJob::ProbeServer do
-  let(:probe_rack_app) do
-    Rack::Builder.app do
-      use GoodJob::Middleware::Healthcheck
-      run GoodJob::Middleware::CatchAll
-    end
-  end
-  let(:probe_server) { described_class.new(app: probe_rack_app, port: port) }
   let(:port) { 3434 }
 
-  after do
-    probe_server.stop
-  end
-
   describe '#start' do
-    it 'starts a http server that binds to all interfaces' do
-      probe_server.start
-      wait_until(max: 1) { expect(probe_server).to be_running }
+    context 'with the default healthcheck app' do
+      it 'starts a http server that binds to all interfaces and returns healthcheck responses' do
+        probe_server = described_class.new(port: port)
+        probe_server.start
+        wait_until(max: 1) { expect(probe_server).to be_running }
 
-      ip_addresses = Socket.ip_address_list.select(&:ipv4?).map(&:ip_address)
-      expect(ip_addresses.size).to be >= 2
-      expect(ip_addresses).to include("127.0.0.1")
+        ip_addresses = Socket.ip_address_list.select(&:ipv4?).map(&:ip_address)
+        expect(ip_addresses.size).to be >= 2
+        expect(ip_addresses).to include("127.0.0.1")
 
-      aggregate_failures do
-        ip_addresses.each do |ip_address|
-          response = Net::HTTP.get(ip_address, "/", port)
-          expect(response).to eq("OK")
+        aggregate_failures do
+          ip_addresses.each do |ip_address|
+            response = Net::HTTP.get(ip_address, "/", port)
+            expect(response).to eq("OK")
 
-          response = Net::HTTP.get(ip_address, "/status", port)
-          expect(response).to eq("OK")
+            response = Net::HTTP.get(ip_address, "/status", port)
+            expect(response).to eq("OK")
 
-          response = Net::HTTP.get(ip_address, "/status/started", port)
-          expect(response).to eq("Not started")
+            response = Net::HTTP.get(ip_address, "/status/started", port)
+            expect(response).to eq("Not started")
 
-          response = Net::HTTP.get(ip_address, "/status/connected", port)
-          expect(response).to eq("Not connected")
+            response = Net::HTTP.get(ip_address, "/status/connected", port)
+            expect(response).to eq("Not connected")
+
+            response = Net::HTTP.get(ip_address, "/unimplemented_url", port)
+            expect(response).to eq("Not found")
+          end
         end
+
+        probe_server.stop
+      end
+    end
+
+    context 'with a provided app' do
+      it 'starts a http server that binds to all interfaces and returns healthcheck responses' do
+        app = Proc.new { [ 200, { "Content-Type" => "text/plain" }, ["Hello World"] ] }
+        probe_server = described_class.new(app: app, port: port)
+        probe_server.start
+        wait_until(max: 1) { expect(probe_server).to be_running }
+
+        ip_addresses = Socket.ip_address_list.select(&:ipv4?).map(&:ip_address)
+        expect(ip_addresses.size).to be >= 2
+        expect(ip_addresses).to include("127.0.0.1")
+
+        aggregate_failures do
+          ip_addresses.each do |ip_address|
+            response = Net::HTTP.get(ip_address, "/", port)
+            expect(response).to eq("Hello World")
+          end
+        end
+
+        probe_server.stop
       end
     end
   end