Confirmed via packet capture: a Yealink phone and (per RouterOS's known
default behavior) the fleet's routers send classic BSD-style syslog,
not RFC5424. Alloy's loki.source.syslog defaults to RFC5424-only and
was silently dropping every message ("expecting a version value in the
range 1-999"). syslog_format = "rfc3164" fixes it, but that argument
only exists from Alloy v1.5.0 onward (confirmed empirically against
v1.4.3, which fails config load) — bump the pin accordingly. v1.5.0 is
an adjacent minor release, not the kind of large version jump that hit
the Loki/Grafana :latest kernel-incompatibility bug fixed earlier.
Alloy receives syslog on 514/udp and 1514/tcp from network devices,
forwards to a local Loki instance; Grafana provisioned with Loki as
default datasource. Compose bind-mounts config from
/mnt/containers/logging/... on the host (staged separately) since
Portainer's GitOps pull only fetches the compose file, not the repo's
other files.
pipistrello