After upgrading Apache httpd to version 2.4.63 or later, users may see the following error when accessing their environments that use an AWS Application Load Balancer (ALB):
421 Misdirected Request: The client needs a new connection for this request as the requested host name does not match the Server Name Indication (SNI) in use for this connection.
A change introduced in Apache httpd 2.4.63 (and versions after) affects how the server handles SNI matching for connections routed through an AWS ALB, causing Apache to reject requests with a 421 Misdirected Request.
This is a known incompatibility between Apache httpd 2.4.63+ and AWS ALB configurations. The issue is documented in the AWS community forum: Misdirected Request with Apache 2.4.52+ behind ALB.
The recommended resolution is to revert the Apache httpd upgrade to a version prior to 2.4.63.
This article applies to all self-managed versions of Appian using Apache httpd 2.4.63 and later, and have ALB in their environment.
Last Reviewed: June 2026