diff options
| -rw-r--r-- | plugin/loop/README.md | 23 | ||||
| -rw-r--r-- | plugin/loop/loop.go | 15 | ||||
| -rw-r--r-- | plugin/loop/setup.go | 1 |
3 files changed, 28 insertions, 11 deletions
diff --git a/plugin/loop/README.md b/plugin/loop/README.md index 5062dfa3d..ee5029fd7 100644 --- a/plugin/loop/README.md +++ b/plugin/loop/README.md @@ -7,10 +7,10 @@ ## Description The *loop* plugin will send a random probe query to ourselves and will then keep track of how many times -we see it. If we see it more than twice, we assume CoreDNS is looping and we halt the process. +we see it. If we see it more than twice, we assume CoreDNS has seen a forwarding loop and we halt the process. The plugin will try to send the query for up to 30 seconds. This is done to give CoreDNS enough time -to start up. Once a query has been successfully sent *loop* disables itself to prevent a query of +to start up. Once a query has been successfully sent, *loop* disables itself to prevent a query of death. The query sent is `<random number>.<random number>.zone` with type set to HINFO. @@ -36,22 +36,24 @@ forwards to it self. After CoreDNS has started it stops the process while logging: ~~~ txt -plugin/loop: Forwarding loop detected in "." zone. Exiting. See https://coredns.io/plugins/loop#troubleshooting. Probe query: "HINFO 5577006791947779410.8674665223082153551.". +plugin/loop: Loop (127.0.0.1:55953 -> :1053) detected for zone ".", see https://coredns.io/plugins/loop#troubleshooting. Query: "HINFO 4547991504243258144.3688648895315093531." ~~~ ## Limitations -This plugin only attempts to find simple static forwarding loops at start up time. To detect a loop, all of the following must be true +This plugin only attempts to find simple static forwarding loops at start up time. To detect a loop, +the following must be true: -* the loop must be present at start up time. -* the loop must occur for at least the `HINFO` query type. +* the loop must be present at start up time. + +* the loop must occur for the `HINFO` query type. ## Troubleshooting -When CoreDNS logs contain the message `Forwarding loop detected ...`, this means that -the `loop` detection plugin has detected an infinite forwarding loop in one of the upstream -DNS servers. This is a fatal error because operating with an infinite loop will consume -memory and CPU until eventual out of memory death by the host. +When CoreDNS logs contain the message `Loop ... detected ...`, this means that the `loop` detection +plugin has detected an infinite forwarding loop in one of the upstream DNS servers. This is a fatal +error because operating with an infinite loop will consume memory and CPU until eventual out of +memory death by the host. A forwarding loop is usually caused by: @@ -64,6 +66,7 @@ to another DNS server that is forwarding requests back to CoreDNS. If `proxy` or using a file (e.g. `/etc/resolv.conf`), make sure that file does not contain local addresses. ### Troubleshooting Loops In Kubernetes Clusters + When a CoreDNS Pod deployed in Kubernetes detects a loop, the CoreDNS Pod will start to "CrashLoopBackOff". This is because Kubernetes will try to restart the Pod every time CoreDNS detects the loop and exits. diff --git a/plugin/loop/loop.go b/plugin/loop/loop.go index 45bdc4267..8d29798ad 100644 --- a/plugin/loop/loop.go +++ b/plugin/loop/loop.go @@ -19,6 +19,7 @@ type Loop struct { zone string qname string + addr string sync.RWMutex i int @@ -49,7 +50,7 @@ func (l *Loop) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) ( } if l.seen() > 2 { - log.Fatalf("Forwarding loop detected in \"%s\" zone. Exiting. See https://coredns.io/plugins/loop#troubleshooting. Probe query: \"HINFO %s\".", l.zone, l.qname) + log.Fatalf(`Loop (%s -> %s) detected for zone %q, see https://coredns.io/plugins/loop#troubleshooting. Query: "HINFO %s"`, state.RemoteAddr(), l.address(), l.zone, l.qname) } return plugin.NextOrFailure(l.Name(), l.Next, ctx, w, r) @@ -94,3 +95,15 @@ func (l *Loop) disabled() bool { defer l.RUnlock() return l.off } + +func (l *Loop) setAddress(addr string) { + l.Lock() + defer l.Unlock() + l.addr = addr +} + +func (l *Loop) address() string { + l.RLock() + defer l.RUnlock() + return l.addr +} diff --git a/plugin/loop/setup.go b/plugin/loop/setup.go index ba4681cb4..db6821341 100644 --- a/plugin/loop/setup.go +++ b/plugin/loop/setup.go @@ -41,6 +41,7 @@ func setup(c *caddy.Controller) error { addr := net.JoinHostPort(lh, conf.Port) for time.Now().Before(deadline) { + l.setAddress(addr) if _, err := l.exchange(addr); err != nil { l.reset() time.Sleep(1 * time.Second) |