Magento - Avoid Cookie Conflict Between Multiple Subdomain Instances

magento_avoid_cookie_conflicts.md

Magento cookies can conflict when a user tries to log in on a subdomain instance due to how cookies are handled in relation to domains and subdomains. Here’s a detailed explanation of why this conflict occurs:

Cookie Domain Scope

1. Domain Scope of Cookies:
   • Cookies set on a main domain (e.g., example.com) can be accessible to all its subdomains (e.g., sub.example.com).
   • Cookies set on a subdomain (e.g., sub.example.com) are not accessible to the main domain (example.com) or other sibling subdomains (another.sub.example.com).
2. Magento Cookie Settings:
   • Magento uses cookies to store session data, user preferences, and authentication tokens.
   • If Magento is not configured correctly to handle cookies across different subdomains, conflicts can arise.

Common Issues and Causes

1. Cookie Path:
   • The path attribute of a cookie defines the URL scope for which the cookie is valid.
   • If the path is not set correctly, cookies from the main domain or other subdomains might interfere with the current subdomain’s session.
2. Cookie Domain Attribute:
   • The domain attribute of a cookie determines the domain(s) for which the cookie is valid.
   • If the domain attribute is set to the main domain (e.g., .example.com), the cookie is shared across all subdomains, which can lead to conflicts if different Magento instances are running on different subdomains.
3. Session Cookie Conflicts:
   • Each Magento instance uses a session cookie to maintain user sessions.
   • If multiple Magento instances on subdomains share the same cookie domain, the session - cookie from one instance can overwrite the session cookie from another, causing login issues and session conflicts.

Preferred Solution

If you don't want to update the main domain (usually a production environment) but still need to fix cookie conflict issues on lower instances or a separate Magento website instance running on a subdomain, here is what you can do:

1. Magento Configuration

   • In the Magento admin panel, navigate to Stores > Configuration > Web > Default Cookie Settings.
   • Set the Cookie Domain to the specific subdomain for each Magento instance. For example, if the subdomain instance URL is stage.example.com, enter stage.example.com into the field and hit the Save button.

2. PHP .ini Configuration

   • Update the session.cookie_domain and session.name values for the subdomain instance in one of the following places, depending on the server setup:
     • pub/.user.ini file from the Magento root directory. (recommended)
     • pub/.htaccess file from the Magento root directory.
     • Find the loaded .ini files from the server with the help of the php -i | grep 'php.ini' command.

   session.cookie_domain = "stage.example.com"
   session.name = "stage_PHPSESSID"

Basically, it changes the session cookie name from PHPSESSID to stage_PHPSESSID and also sets the cookie_domain to stage.example.com. After this, customer login will work fine even without clearing the browser cookies.