udp_proxy will combine multiple message to one package

[rainbowwiki]

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Title: udp_proxy will combine multiple message to one package

Description:

I am using envoy as a proxy to accept syslog by udp_proxy, but found once sent to rsyslog directly, the package is correct, but if send to envoy then envoy sent to rsyslog, some package will combine, and I did the tcpdump after envoy, found if package from envoy , then some package met this issue.

Repro steps:

I will provide ths snapshot

Envoy version is from 1.18 / 1.35.1 / 1.36-latest, both this issue

thanks!

[phlax]

cc @mattklein123 @danzh2010

[rainbowwiki]

hello team,

I found this case and did many test

1. envoy docker bridge network -> work well
2. envoy docker host network -> multple message to one package
3. envoy rpm directly -> multple message to one package
4. nginx docker host network -> work well
   .....

for my understanding : envoy seems read the socket buffer one time, and send to backend

so I want to know Is there a special mechanism? seems envoy forward to backend will use session and maybe merge multple message to one package ?

thanks!