Fluentbit creates TCP connections - windows

Question

Fluentbit creates TCP connections to itself?
What are these used for?
fluent.conf file:
[SERVICE]
Flush 5
Daemon Off
Log_Level debug
[INPUT]
Name tail
Tag format.logging
path C:\Logs\*main.log
DB C:\Logs\main_logs.db
[OUTPUT]
Name stdout
Match *

Answer 1

This seems to boil down to an implementation detail where it uses unix sockets on Linux for its event loop, but on Windows it has opted to using localhost-connections.
Comment from https://github.com/fluent/fluent-bit/blob/37aa680d32384c1179f02ee08a5bef4cd278513e/lib/monkey/mk_core/deps/libevent/include/event2/util.h#L380
/** Create two new sockets that are connected to each other.
On Unix, this simply calls socketpair(). On Windows, it uses the
loopback network interface on 127.0.0.1, and only
AF_INET,SOCK_STREAM are supported.
(This may fail on some Windows hosts where firewall software has cleverly
decided to keep 127.0.0.1 from talking to itself.)
Parameters and return values are as for socketpair()
*/
The actual implementation is here: https://github.com/fluent/fluent-bit/blob/37aa680d32384c1179f02ee08a5bef4cd278513e/lib/monkey/mk_core/deps/libevent/evutil.c#L207
It matches the pattern when looking at the netstat output:
netstat -anop tcp | findstr <fluentbit pid>
TCP 127.0.0.1:54645 127.0.0.1:54646 ESTABLISHED 12012 \
TCP 127.0.0.1:54646 127.0.0.1:54645 ESTABLISHED 12012 ´` Pair
TCP 127.0.0.1:54647 127.0.0.1:54648 ESTABLISHED 12012 \
TCP 127.0.0.1:54648 127.0.0.1:54647 ESTABLISHED 12012 ´` Pair