Hello @myrbourfak618d ,
I totally agree with your point that this should not be happening as it affects the SEO a lot and some integrations throws exception of duplicate pages.
I am sharing a solution below which will help you to redirect your off domains to default store with store code and if URL contains any store code, it will work without any bothering.
Create module with below files :
1. registration.php
<?php
Magento\Framework\Component\ComponentRegistrar::register(
\Magento\Framework\Component\ComponentRegistrar::MODULE,
'Vendor_Module',
__DIR__
);2. module.xml
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
<module name="Vendor_Module" setup_version="1.0.0">
</module>
</config>3. etc/frontend/events.xml
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
<event name="controller_action_predispatch">
<observer name="force_storecode_redirect" instance="Vendor\Module\Observer\ForceStorecodeRedirectObserver" shared="false" />
</event>
</config>4. Observer/ForceStorecodeRedirectObserver.php
<?php
namespace Vendor\Module\Observer;
use Magento\Framework\Event\ObserverInterface;
class ForceStorecodeRedirectObserver implements ObserverInterface
{
protected $storeManager;
protected $url;
/** @var array $storeCodes - array of existing storecodes*/
protected $storeCodes = [];
public function __construct(
\Magento\Store\Model\StoreManagerInterface $storeManager,
\Magento\Framework\UrlInterface $url
) {
$this->storeManager = $storeManager;
$this->url = $url;
$this->storeCodes = array_keys($this->storeManager->getStores(false, true));
}
public function execute(\Magento\Framework\Event\Observer $observer)
{
$urlParts = parse_url($this->url->getCurrentUrl());
$path = $urlParts['path'];
// get storecode from URL
$urlCode = trim(substr($path, 0, 4), '/');
// If path does not already contain an existing storecode
if (!in_array($urlCode, $this->storeCodes)) {
header("HTTP/1.1 301 Moved Permanently");
header("Location: " . $this->storeManager->getStore()->getBaseUrl() . substr($path, 1));
exit();
}
}
}
I hope it helps ! 
regarding nginx redirection :
Definitely the nginx would be faster because it would not reach to magento code and it would not process anything till then but in that case you have to manually put store codes and if you edit/add new store code you have to remember that and need to implement again. But with Magento’s customisation it would also not take huge time as it’s just comparing the store code but you don’t need to worry about store code modifications. So I would recommend the Magento redirection.
Home Page redirection :
Yes, remove 33 line condition as I copied from my earlier implementation where we had the country selector on home page and landing page was with store code. It will work perfectly after removing that.
PS : I have edited my solution and removed that condition.
Hope it helps !
No, there will not be any issue with SEO.
