Duplicate health monitor behavior in Avi

Products

• VMware Avi Load Balancer

Issue/Introduction

Duplicate health monitor behavior in Avi

Environment

- Multiple pools configured with the same health monitor and server combination.

Cause

- By default, multiple instances of the same health monitor to the same server are suppressed intelligently.
- Say that we have a server, 10.10.10.10, with the same HM, "custom-hm", configured on 2 pools, Pool1 and Pool2.
- If the VS associated to Pool1 is placed first, the SE will add the "custom-hm" for server 10.10.10.10.
- Now when the VS for Pool2 is placed on the same SE, the same HM will NOT be added since one instance of it is already active.

Resolution

- In rare cases, the monitor may have specific constructs that go beyond the server keys (ip, port, etc.) during which such suppression is not desired. 
- One such use case might be when there is a HTTPS HM configured on the pool. With the HTTPS-HM, there are SSL attributes that are associated. They can either be added to the HM config or inherited from the pool config.
- When inheriting from the pool config, if the same HM/server config is added to multiple pools with different SSL profiles, only the first pools SSL config will be used to do the health checks.
- Even if the SSL profiles are different, the subsequent ones will not be used. 
- To allow duplicate HMs, there is a knob called allow_duplicate_monitors in the HM config. This knob is immutable and is only configurable from the CLI at the time of creation.

[admin:<cntlr-ip>]: > configure healthmonitor https-custom
 ...
[admin:<cntlr-ip>]: healthmonitor> allow_duplicate_monitors
[admin:<cntlr-ip>]: healthmonitor> save

 

- The other workaround would be to configure a unique HM for each pool.