Code change:
return ret } <del> // continuousEcho() uses the same connection for multiple requests, made to run as a goroutine so that // manipulations can be made to the service and backend pods while a connection is ongoing // it starts by sending a series of packets to establish conntrack entries and waits for a signal to keep // sending packts. It returns an error if the number of failed attempts is >= 5 func continuousEcho(host string, port int, timeout time.Duration, maxAttempts int, signal chan struct{}, errorChannel chan error) { defer ginkgo.GinkgoRecover() const threshold = 10 // Sanity check inputs, because it has happened.  These are the only things // that should hard fail the test - they are basically ASSERT()s. if host == "" { errorChannel <- fmt.Errorf("Got empty host for continuous echo (%s)", host) return } if port == 0 { errorChannel <- fmt.Errorf("Got port ==0 for continuous echo (%d)", port) return } hostPort := net.JoinHostPort(host, strconv.Itoa(port)) url := fmt.Sprintf("udp://%s", hostPort) ret := UDPPokeResult{} con, err := net.Dial("udp", hostPort) if err != nil { ret.Status = UDPError ret.Error = err errorChannel <- fmt.Errorf("Connection to %q failed: %v", url, err) return } numErrors := 0 bufsize := len(strconv.Itoa(maxAttempts)) + 1 var buf = make([]byte, bufsize) for i := 0; i < maxAttempts; i++ { if i == threshold { framework.Logf("Continuous echo waiting for signal to continue") <-signal if numErrors == threshold { errorChannel <- fmt.Errorf("continuous echo was not able to communicate with initial server pod") return } } time.Sleep(1 * time.Second) err = con.SetDeadline(time.Now().Add(timeout)) if err != nil { ret.Status = UDPError ret.Error = err framework.Logf("Continuous echo (%q): %v", url, err) numErrors++ continue } myRequest := fmt.Sprintf("echo %d", i) _, err = con.Write([]byte(fmt.Sprintf("%sn", myRequest))) if err != nil { ret.Error = err neterr, ok := err.(net.Error) if ok && neterr.Timeout() { ret.Status = UDPTimeout } else if strings.Contains(err.Error(), "connection refused") { ret.Status = UDPRefused } else { ret.Status = UDPError } numErrors++ framework.Logf("Continuous echo (%q): %v - %d errors seen so far", url, err, numErrors) continue } err = con.SetDeadline(time.Now().Add(timeout)) if err != nil { ret.Status = UDPError ret.Error = err numErrors++ framework.Logf("Continuous echo (%q): %v - %d errors seen so far", url, err, numErrors) continue } n, err := con.Read(buf) if err != nil { ret.Error = err neterr, ok := err.(net.Error) if ok && neterr.Timeout() { ret.Status = UDPTimeout } else if strings.Contains(err.Error(), "connection refused") { ret.Status = UDPRefused } else { ret.Status = UDPError } numErrors++ framework.Logf("Continuous echo (%q): %v - %d errors seen so far", url, err, numErrors) continue } ret.Response = buf[0:n] if string(ret.Response) != fmt.Sprintf("%d", i) { ret.Status = UDPBadResponse ret.Error = fmt.Errorf("response does not match expected string: %q", string(ret.Response)) framework.Logf("Continuous echo (%q): %v", url, ret.Error) numErrors++ continue } ret.Status = UDPSuccess framework.Logf("Continuous echo(%q): success", url) } err = nil if numErrors >= threshold { err = fmt.Errorf("Too many Errors in continuous echo") } errorChannel <- err } </del> // testReachableUDP tests that the given host serves UDP on the given port. func testReachableUDP(host string, port int, timeout time.Duration) { pollfn := func() (bool, error) {

Related discussion:
text: After my second deflaking PR, we seem to be in the stage where: tests are failing on dozens of different things (probably iptables-issues related) tests are failing only on NodePort tests on "Failed to connecto to backend 1" which it would be great if someone else could look into (kube-proxy seemed to be programmed correctly based on logs)
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This has failed again - Linking to specific part of log where timeout occurred .... we see this
So reviewing the above logs note how in STEP: checking client pod connected to the backend 1 on Node IP 10.138.0.5 28 attempts are made all in the 25th second of the 2 minute at 11am Should this Step back off and wait a few seconds in between tries? So looking at this code we see the following
From reading ... the intention expressed in the test code looks good to me. It is not clear to me why there is a mismatch between the 28 tries in the POD Client Logs and the expressed intention running the logContainsFn(podBackend1) every 5 seconds still digging ....
we are trying to catch one failure in this PR that has additional debugging, it dumps the conntrack table of the nodes on a failure
for those following the issue, we've extra debugging to the test so it dumps the whole conntrack table once it finish. We should look that there is NO stale entries, connections from the pod client to the deleted endpoint) and there is conntrack entries to the new endpoint from the pod client.
- we have runs with the conntrack dump now, e.g. this one: would you be able to take a look into it?
not yet :/ , but I think tomorrow can have some time
cc
For anyone reproducing this issue btw, you need a multinode k8s cluster (it isnt doable on kind i guess bc less likeliehood of network failures when running local) -
Curious about two potential hypotheses to fix this, have we looked into either of these? 1) can we confirm that is turned on/off? 2) is it possible that scaling the number of coredns replicas could help ?