Knox returns HTTP 405 Method Not Allowed error with HTTP HEAD method

Load balancer (Netscalar) probes receives HTTP 405 Method Not Allowed errors from Knox with HEAD request. Doing a HEAD requests is the preferred (and common) way to probe status of a service from LB's.

Test as follows:

curl -k --head  https://gateway.domain.com:8443/gateway/default/ambari/

Knoxgateway-audit.log gives this error:

17/09/25 17:46:04 ||60da43b2-97c3-4d32-ac10-b6d566a69e90|audit|AMBARIUI||||authorization|uri|/gateway/default/ambari|success|
17/09/25 17:46:04 ||60da43b2-97c3-4d32-ac10-b6d566a69e90|audit|AMBARIUI||||access|uri|/gateway/default/ambari|success|Response status: 405
17/09/25 17:46:04 ||36137fd2-3643-4225-943d-1213cb0bfafd|audit|||||access|uri|/gateway/default/yarngateway/default/ambari|unavailable|Request method: HEAD
17/09/25 17:46:04 ||36137fd2-3643-4225-943d-1213cb0bfafd|audit|||||access|uri|/gateway/default/yarngateway/default/ambari|success|Response status: 404
17/09/25 17:46:09 ||1e4f6bce-cbf7-43da-858d-d43166fa1dcb|audit|||||access|uri|/gateway/default/yarngateway/default/ambari|unavailable|Request method: HEAD

The error is coming from Knox. When doing the same curl directly to Ambari, we get an HTTP 200 back.