503 responses being treated as Service OK

[krausyd]

I am running a Slow body for penetration testing for my service. I am working in some mitigations for the DoS when slow http happens. When I have my service under attack, I do some real request to see if my service is up or not. And I get a 503 on those requests, and when I see my service dashboards, clearly it was overloaded, and restarted by my balancers due bad health.

But when I see the graphs and report generated from my test, it says my service was available 100% of the time. Shouldn't it show as unavailable?

The command I am running is:
slowhttptest -u <my_url> -c 10000 -B -g -v4

I can see the 503 responses in the logs:

Sat May 27 11:50:26 2023:
slow HTTP test status on 0th second:

initializing:        0
pending:             1
connected:           0
error:               0
closed:              0
service available:   YES

foo=barSat May 27 11:50:28 2023:socket 75 created 
Sat May 27 11:50:28 2023:run_test:initial 385 of 385 bytes sent on socket 70:
POST / HTTP/1.1
Host: <my_url>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:5.0.1) msnbot-131-253-46-102.search.msn.com
Referer: TESTING_PURPOSES_ONLY
Content-Length: 4096
Content-Type: application/x-www-form-urlencoded
Accept: text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Connection: close

foo=barSat May 27 11:50:28 2023:socket 80 created 
Sat May 27 11:50:28 2023:run_test:initial 385 of 385 bytes sent on socket 75:
POST / HTTP/1.1
Host: <my_url>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:5.0.1) msnbot-131-253-46-102.search.msn.com
Referer: TESTING_PURPOSES_ONLY
Content-Length: 4096
Content-Type: application/x-www-form-urlencoded
Accept: text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Connection: close
Sat May 27 11:50:31 2023:
slow HTTP test status on 5th second:

initializing:        0
pending:             6
connected:           193
error:               0
closed:              11
service available:   YES
Sat May 27 11:50:32 2023:run_test: socket 75 replied 147 bytes:
HTTP/1.1 503 Service Unavailable
Date: Sat, 27 May 2023 18:50:32 GMT
Content-Length: 0
Connection: close
x-amz-request-id: D089F0EFCC0BF7C6

Sat May 27 11:50:32 2023:run_test: socket 75 closed: Peer closed connection

Sat May 27 11:50:36 2023:
slow HTTP test status on 10th second:

initializing:        0
pending:             6
connected:           190
error:               0
closed:              212
service available:   YES

This is the graph:

This is the csv data:

You can see that second 6, when that socket was closed due 503, is shown as Service Available.

[shekyan]

The tool doesn't account for intermediaries (load balancers), and as long as new connection can be established and there is a response coming back - tool considers the service alive.