Illegal request, responding with status '505 HTTP Version Not Supported': The server does not support the HTTP protocol version used in the request.

[Ranga_Tolapi]

Hi, There

Today started noticing the below warnings in ArcGIS Workflow Manager Server logs in large quantity at an average interval of 10-15sec.

<Msg time="2023-08-28T22:11:43,710" type="WARNING" code="9999" source="WorkflowManager" process="22468" thread="19" methodName="" machine="XXX" user="" elapsed="" requestID="">Illegal request, responding with status '505 HTTP Version Not Supported': The server does not support the HTTP protocol version used in the request.</Msg>

Can someone throw some light on what is causing these warnings, is something to worry about and how to address it.

Thank you.

ArcGIS Workflow Manager Server version is 10.9.1

[RandallWilliams]

Looks like your front end web server may only support HTTP/2, where Workflow Manager likely requires HTTP/1.1. - or potentially vice-versa.  Because the front end is sending in a format than the back-end server expects, an error is thrown. 

[Ranga_Tolapi · Accepted solution]

You are right @RandallWilliams, thank you for the right direction.

Root cause is our F5 load balancer health monitor's health check URLs.

As explained here, The BIG-IP system, by default, uses HTTP 0.9 when sending monitor requests, if HTTP version is not explicitly mentioned in the request.

Finally, the below health check settings worked well with F5 load balancer's pool for Workflow Manager Servers.

Send String:
GET /workflow/healthCheck HTTP/1.1\r\nHost: <FQDN>\r\nAccept: application/json\r\nConnection: Close\r\n\r\n
Receive String:
200

[Ranga_Tolapi]

Noted @RandallWilliams, thanks.

How to find what is the source (IP or Hostname) of such requests from the ArcGIS Server logs or any other logs?

IIS logs captures the requestor IP, any such arrangements available for ArcGIS Server?

[RandallWilliams]

Web server logs will be the best way to collect this information. 

[Ranga_Tolapi]

In our environment, requests are not only coming from web server but from other sources too e.g. load balancer. I thought of finding the Requester details from ArcGIS Server (the Responder).