An egress spell masked a service on the surviving network going down: with
`peerResponded` set only by the DNS and gRPC providers, every other failure fell
back to the HTTP-status heuristic, which answers "nothing replied" for anything
that is not speaking HTTP. A refused connection on the local network was read as
the instance's own loss of egress, so the check was recorded as degraded and the
monitor stayed up.
`peerAnsweredFromError` holds the errno codes that require the target's own stack
to have replied — a refusal, a reset, a TLS handshake that got as far as a
certificate. Http, Port, WebSocket and Docker use it; Http also treats any status
code as an answer, and Docker any status from the daemon. Hardware and PageSpeed
go through Http and inherit it.
`true` is the claim that costs something, since it blames the target, so it is
only set on evidence. Two cases stay conservative and are commented as such: a
ping that draws no echo reply, and a gamedig query that fails, neither of which
can be told apart from the instance losing its egress. Nor can a proxied HTTP
request that fails with no response, where the refusal may be the proxy's.
🔧
Alex Holliday
Craig Lawson