libnet: don't put external DNS answers in OTel spans

akerouanton · akerouanton · commit 173a9f20910e · 2024-11-08T17:32:39.000+01:00
When containers make DNS resolution, and the domain name they're trying
to resolve doesn't match any running container, the DNS query is
forwarded to upstream servers. In that case, when we receive a response,
we put it in an OTel spans.

This was useful to debug DNS resolution on GHA, but it leads to
excessive memory usage when DNS resolution happen in a tight loop. So,
keep the OTel event signaling that a response was received, but drop the
answer from the OTel span.

Signed-off-by: Albin Kerouanton &lt;albinker@gmail.com&gt;
diff --git a/libnetwork/resolver.go b/libnetwork/resolver.go
@@ -600,9 +600,7 @@ func (r *Resolver) forwardExtDNS(ctx context.Context, proto string, remoteAddr n
 			r.log(ctx).Debugf("[resolver] external DNS %s:%s returned response with no answers:\n%s", proto, extDNS.IPStr, resp)
 		}
 		resp.Compress = true
-		span.AddEvent("response from upstream server", trace.WithAttributes(
-			attribute.String("libnet.resolver.resp", resp.String()),
-		))
+		span.AddEvent("response from upstream server")
 		return resp
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -600,9 +600,7 @@ func (r *Resolver) forwardExtDNS(ctx context.Context, proto string, remoteAddr n`
`600`	`600`	`r.log(ctx).Debugf("[resolver] external DNS %s:%s returned response with no answers:\n%s", proto, extDNS.IPStr, resp)`
`601`	`601`	`}`
`602`	`602`	`resp.Compress = true`
`603`		`- span.AddEvent("response from upstream server", trace.WithAttributes(`
`604`		`- attribute.String("libnet.resolver.resp", resp.String()),`
`605`		`- ))`
	`603`	`+ span.AddEvent("response from upstream server")`
`606`	`604`	`return resp`
`607`	`605`	`}`
`608`	`606`