F5 external load balancer configuration monitor for NSX Manager cluster failing with "426 Upgrade Required" error after upgrading NSX environment to version 4.2

Products

• VMware NSX

Issue/Introduction

• F5 external load balancer configuration monitor for NSX Manager cluster worked properly on NSX version 3.x. 
• After upgrading NSX Managers to version 4.2, observe error "426 Upgrade Required" response for F5 external load balancer monitor. 

Environment

F5 BIG-IP External Load Balancer

VMware NSX 4.2

Cause

The F5 BIG-IP system, by default, uses HTTP/0.9 when sending monitor requests which is not accepted by NSX Managers on version 4.2. 

Resolution

Update the F5 external load balancer send string to HTTP/1.1. 

i.e. 

GET /api/v1/reverse-proxy/node/health HTTP/1.1\r\nHost: monitor-hostname-example\r\ncontent-type: application/json\r\nAccept: application/json\r\nConnection: Close\r\n\r\n

Additional Information

Link to document for Configuring an External Load Balancer. 

F5 KB 2167 with additional details related to this F5 behavior.