Maintenance Mode is not going to 503 Page

Question

Normally when you enter maintenance Mode, Magento is supposed to return a 503 Error, and redirect to a customizable page.

Right now, when I enable maintenance mode, Magento returns a 500 error, and displays the following message:

Unable to proceed: the maintenance mode is enabled. 
#0 /root/vendor/magento/framework/App/Bootstrap.php(256): Magento\Framework\App\Bootstrap->assertMaintenance()
#1 /root/index.php(40): Magento\Framework\App\Bootstrap->run(Object(Magento\Framework\App\Http))
#2 {main}

Nothing shows up in Magento or server logs. How can I fix this?

Answer 1

Probably you have developer mode enabled. If you take a look at vendor/magento/framework/App/Http.php, method catchException is trying to handle Exception

Unable to proceed: the maintenance mode is enabled.

thrown in vendor/magento/framework/App/Bootstrap.php. and in the case of developer mode it is supposed to send 500 response code. In production mode handleBootstrapErrors method redirects user to errors/503.php:

    /**
     * {@inheritdoc}
     */
    public function catchException(Bootstrap $bootstrap, \Exception $exception)
    {
        $result = $this->handleDeveloperMode($bootstrap, $exception)
            || $this->handleBootstrapErrors($bootstrap, $exception)
            || $this->handleSessionException($exception)
            || $this->handleInitException($exception)
            || $this->handleGenericReport($bootstrap, $exception);
        return $result;
    }

    /**
     * Error handler for developer mode
     *
     * @param Bootstrap $bootstrap
     * @param \Exception $exception
     * @return bool
     */
    private function handleDeveloperMode(Bootstrap $bootstrap, \Exception $exception)
    {
        if ($bootstrap->isDeveloperMode()) {
            if (Bootstrap::ERR_IS_INSTALLED == $bootstrap->getErrorCode()) {
                try {
                    $this->redirectToSetup($bootstrap, $exception);
                    return true;
                } catch (\Exception $e) {
                    $exception = $e;
                }
            }
            $this->_response->setHttpResponseCode(500);
            $this->_response->setHeader('Content-Type', 'text/plain');
            $this->_response->setBody($exception->getMessage() . "\n" . $exception->getTraceAsString());
            $this->_response->sendResponse();
            return true;
        }
        return false;
    }
    /**
     * Handler for bootstrap errors
     *
     * @param Bootstrap $bootstrap
     * @param \Exception &$exception
     * @return bool
     */
    private function handleBootstrapErrors(Bootstrap $bootstrap, \Exception &$exception)
    {
        $bootstrapCode = $bootstrap->getErrorCode();
        if (Bootstrap::ERR_MAINTENANCE == $bootstrapCode) {
            require $this->_filesystem->getDirectoryRead(DirectoryList::PUB)->getAbsolutePath('errors/503.php');
            return true;
        }
        if (Bootstrap::ERR_IS_INSTALLED == $bootstrapCode) {
            try {
                $this->redirectToSetup($bootstrap, $exception);
                return true;
            } catch (\Exception $e) {
                $exception = $e;
            }
        }
        return false;
    }