Your customer has recently experienced a large uptick in traffic and added a second server. After the new server went online users started reporting…

The core issue is the loss of session data in a multi-server, load-balanced environment. When sessions are stored on the local file system, each server maintains its own separate session files. If a user's request is routed to a different server than their previous one, the new server cannot access the original session data, leading to a lost cart. To resolve this, session storage must be centralized so all web servers can access it. Both saving sessions to a shared database or to a Redis instance are standard, supported methods in Adobe Commerce for centralizing session storage and ensuring persistence across a server cluster.

A. A custom URL for the cart is a front-end or routing change and does not address the back-end session storage location.

B. Eliminating the load balancer would defeat the purpose of adding a second server for high availability and traffic distribution.

1. Adobe Commerce Developer Documentation

Configure sessions: "By default

Adobe Commerce stores sessions in files. This can be problematic in a production environment with a load balancer and multiple web nodes. A user’s subsequent request can go to a different node

resulting in the loss of the user’s shopping cart and other information. To avoid this

you can store sessions in the database or in Redis." This document explicitly identifies the problem and presents saving sessions to the database or Redis as the solutions.

Source: Adobe Commerce Developer Documentation > Configuration Guide > Performance > Configure sessions.

2. Adobe Commerce Developer Documentation

Session size best practices: This document outlines the different mechanisms for session storage available in Adobe Commerce. It lists "File system"

"Database"

and "Redis" as the primary options

confirming that the database and Redis are valid alternatives to the problematic file system storage in a multi-server setup.

Source: Adobe Commerce Developer Documentation > Best practices > Performance > Session size best practices > Session storage.