feat: warn when incorrect interface/port in use for web processes

Users that misconfigure their process's listening interface or port will now see an additional healthcheck warning for web deploys. While only a single port is checked, this ensures that users at least have some context as to why their app isn't responding as expected.

Closes #4798

tests/apps/python/web.py

@@ -31,7 +31,10 @@ if __name__ == "__main__":
     for arg in sys.argv:
         print(f"Arg: {arg}")
 
-    port = int(os.getenv("PORT", 5000))
+    port = int(os.getenv("PORT", "5000"))
+    if os.getenv("ALT_PORT"):
+        port = int(os.getenv("ALT_PORT", "5000"))
+
     server = http.server.HTTPServer(("0.0.0.0", port), GetHandler)
     print("Listening on port {0}".format(port))
     server.serve_forever()

tests/unit/checks.bats

@@ -268,3 +268,21 @@ teardown() {
   assert_output_contains "/healthcheck"
   assert_success
 }
+
+@test "(checks) listening checks" {
+  if [[ "$TERM_PROGRAM" == "vscode" ]]; then
+    skip "environment must be running in the host namespace"
+  fi
+
+  run /bin/bash -c "dokku config:set $TEST_APP ALT_PORT=5001"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run deploy_app
+  echo "output: $output"
+  echo "status: $status"
+  assert_failure
+  assert_output_contains "Failure in name='port listening check': container listening on expected IPv4 interface with an unexpected port: expected=5000 actual=5001"
+  assert_output_contains "Running healthcheck name='port listening check' attempts=3 port=5000 retries=2 timeout=5 type='listening' wait=5"
+}