On the release day, an AEM code deployment is done on AEM 6.5 on-prem. After the deployment was completed, the users were able to get into the Author instance with no issues. However, users are unable to access any of the sites on public domains. The users are seeing a "502 Bad Gateway" error. What would be the potential cause of this issue?

A "502 Bad Gateway" error indicates that the Dispatcher (acting as a proxy) received an invalid response from the upstream server, which is the AEM Publish instance. A common cause for this after a deployment is a misconfiguration in the Dispatcher farm file. If the deployment included changes to the farm file's /renders section, such as an incorrect IP address, hostname, or port for the AEM Publish instance, the Dispatcher will be unable to properly connect and forward requests, resulting in a 502 error for all incoming traffic.

A. Increased load on Publish instances would more typically result in a 503 Service Unavailable or 504 Gateway Timeout error, not a 502 Bad Gateway.
B. Stuck replication agents affect content freshness on the Publish instance but do not typically cause the entire instance to become unresponsive or return invalid responses.
D. While unresponsive bundles could cause the Publish instance to fail, a 502 is more specific to a proxy communication failure, making a direct Dispatcher configuration error a more likely cause.

1. Adobe Experience Manager Documentation. (n.d.). Troubleshooting Dispatcher. Adobe Experience League. Retrieved from https://experienceleague.adobe.com/docs/experience-manager-dispatcher/using/troubleshooting/troubleshooting.html (See section "AEM returns a 502 or 503 error," which points to checking connectivity between Dispatcher and AEM).

2. Adobe Experience Manager Documentation. (n.d.). Configuring Dispatcher. Adobe Experience League. Retrieved from https://experienceleague.adobe.com/docs/experience-manager-dispatcher/using/configuring/dispatcher-configuration.html (The /renders section in the farm file defines the backend AEM instances; errors here directly cause gateway errors).