OPM Stations are failing

Products

• CA App Synthetic Monitor

Issue/Introduction

Getting a null response. in OPMS stations

Resolution

The message coming from the failed JMeter Assertion is "Response was null". This is not technically correct, it should be worded "Response was empty" as it is not a result of any kind of internal JMeter error making the response null but just because the server would return an empty response. This wording of the message is what JMeter creators chose, but it's not accurate.
The site being tested is using Akamai CDN so we're getting different IPs on occasions, contacting various servers from our stations, sometimes the stations would always get the same IP, sometimes it would get different IPs but that's to be expected. What is happening behind those IPs is beyond our (ASM) knowledge.

 

Every single empty response is being signalled like this, both in JMeter (that would only use HTTP/1.1):

Content-Length: 0
X-Akamai-Transformed: 9l 0 0 pmb=mRUM,2

and HTTPS (using HTTP/2):

content-length: 0
x-akamai-transformed: 9l 0 0 pmb=mRUM,2

Not sure what x-akamai-transformed header numbers mean, but the Content-Length: 0 are actively and specifically signalling that the server is sending an empty response because with 200 OK response code a response body is being expected.