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MSS clamper check triggers false positives
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Description

Currently, prometheus-lvs-realserver-mss.py is wrongly reporting MSS as 0 intermittently:

image.png (800×3 px, 269 KB)

the script currently uses raw sockets to be able to inspect the TCP header of the SYN/ACK response using scapy. Current theory is that under high network load, the script is unable to parse the response in a timely manner resulting on the MSS being reported as 0

Event Timeline

Vgutierrez renamed this task from MSS clamper clamping check false positives to MSS clamper check triggers false positives.May 16 2024, 8:44 AM

Change #1032400 had a related patch set uploaded (by Vgutierrez; author: Vgutierrez):

[operations/puppet@production] prometheus::lvs: Fetch MSS using getsockopt()

https://gerrit.wikimedia.org/r/1032400

Change #1032400 merged by Vgutierrez:

[operations/puppet@production] prometheus::lvs: Fetch MSS using getsockopt()

https://gerrit.wikimedia.org/r/1032400

removed raw sockets usage. We are now fetching MSS data via getsockopts()