HTTP/App Cookie Persistence might fail on Avi Load Balancer when "Connection Multiplexing" is disabled

Products

• VMware Avi Load Balancer

Issue/Introduction

Intermittent application persistence issues may occur for a Virtual Service configured with an HTTP Cookie or Application Cookie persistence profile.

This issue specifically occurs when the client IPs are being SNATed, and the incoming connections on Avi appear to be coming from a single (or two) IP addresses instead of the original source IPs.

When this issue occurs, you may observe "Persistent server changed" entries in the Virtual Service's significant logs, indicating that client requests are not being consistently sent to the same backend server as directed by the persistence cookie.

Example screenshot of the virtual service significant log:

Environment

Applicable to any version of Avi load balancer.

Cause

This behavior occurs when Connection Multiplexing is disabled in the Virtual Service's Application Profile and the client IPs are source NATed.

When multiplexing is turned off, the connection persistence behavior relies solely on the existing TCP connections between the Avi Service Engine (SE) and pool members.

If cookie-based persistence is used without multiplexing, requests may get routed incorrectly.

Resolution

To resolve this issue, you must enable Connection Multiplexing in the Application Profile attached to the affected Virtual Service.

1. Navigate to Templates > Profiles > Application.

2. Edit the Application Profile used by the Virtual Service.

3. Ensure the Connection Multiplex checkbox is enabled.

4. Save the profile.

Additional Information

HTTP cookie persistence KB: https://techdocs.broadcom.com/us/en/vmware-security-load-balancing/avi-load-balancer/avi-load-balancer/30-2/vmware-avi-load-balancer-configuration-guide/load-balancing-overview/persistence/http-cookie-persistence.html 

App cookie persistence KB: https://techdocs.broadcom.com/us/en/vmware-security-load-balancing/avi-load-balancer/avi-load-balancer/30-2/vmware-avi-load-balancer-configuration-guide/load-balancing-overview/persistence/app-cookie-persistence.html 

Connection Multiplexing KB: https://techdocs.broadcom.com/us/en/vmware-security-load-balancing/avi-load-balancer/avi-load-balancer/30-2/vmware-avi-load-balancer-configuration-guide/load-balancing-overview/application-profile/connection-multiplexing.html