NSX-T Server Pools are down but LB and Virtual Servers are up

Products

• VMware NSX Networking

Issue/Introduction

Symptoms:

• NSX-T Data Center
• Applications behind NSX Load Balancer are inaccessible
• On the UI, Server Pools are reported down
• On the Server Pools configuration, IP Pool has been selected instead of the default Automap
• The SNAT IP configured on the Server Pool is the same IP used for the Virtual Server

Environment

VMware NSX-T Data Center

Cause

This issue can occur if the Virtual Server VIP address is also used as the Server Pool SNAT IP and is configured across multiple Tier-1 Gateways running on different Edges.
This will result in both Tier-1 Edges advertising the same SNAT IP address and disrupting monitor traffic.
The Server Pool monitoring will fail and be reported as down or may be flapping up/down.

Resolution

This is a known issue impacting NSX-T Data Center.

Workaround:
This issue will not be observed if all Virtual Servers and Pools are on 1 Load Balancer.
The issue may only present itself when the working configuration is later scaled out across multiple Tier-1 Gateways and Edge clusters. 

To avoid this issue ensure a unique SNAT IP per pool/VIP combination.
It is recommend to use a different IP address for VIP and SNAT pool address.