If you are using a released version of Kubernetes, you should refer to the docs that go with that version.
The latest 1.0.x release of this document can be found [here](http://releases.k8s.io/release-1.0/docs/user-guide/debugging-services.md).Documentation for other releases can be found at releases.k8s.io.
An issue that comes up rather frequently for new installations of Kubernetes is
that Services are not working properly. You've run all your Pods and
ReplicationControllers, but you get no response when you try to access them.
This document will hopefully help you to figure out what's going wrong.
Table of Contents
- My Service is not working - how to debug
Throughout this doc you will see various commands that you can run. Some
commands need to be run within Pod, others on a Kubernetes Node, and others
can run anywhere you have kubectl and credentials for the cluster. To make it
clear what is expected, this document will use the following conventions.
If the command "COMMAND" is expected to run in a Pod and produce "OUTPUT":
u@pod$ COMMAND
OUTPUTIf the command "COMMAND" is expected to run on a Node and produce "OUTPUT":
u@node$ COMMAND
OUTPUTIf the command is "kubectl ARGS":
$ kubectl ARGS
OUTPUTFor many steps here you will want to see what a Pod running in the cluster
sees. Kubernetes does not directly support interactive Pods (yet), but you can
approximate it:
$ cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
name: busybox-sleep
spec:
containers:
- name: busybox
image: busybox
args:
- sleep
- "1000000"
EOF
pods/busybox-sleepNow, when you need to run a command (even an interactive shell) in a Pod-like
context, use:
$ kubectl exec busybox-sleep -- <COMMAND>or
$ kubectl exec -ti busybox-sleep sh
/ #For the purposes of this walk-through, let's run some Pods. Since you're
probably debugging your own Service you can substitute your own details, or you
can follow along and get a second data point.
$ kubectl run hostnames --image=gcr.io/google_containers/serve_hostname \
--labels=app=hostnames \
--port=9376 \
--replicas=3
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
hostnames hostnames gcr.io/google_containers/serve_hostname app=hostnames 3Note that this is the same as if you had started the ReplicationController with
the following YAML:
apiVersion: v1
kind: ReplicationController
metadata:
name: hostnames
spec:
selector:
app: hostnames
replicas: 3
template:
metadata:
labels:
app: hostnames
spec:
containers:
- name: hostnames
image: gcr.io/google_containers/serve_hostname
ports:
- containerPort: 9376
protocol: TCPConfirm your Pods are running:
$ kubectl get pods -l app=hostnames
NAME READY STATUS RESTARTS AGE
hostnames-0uton 1/1 Running 0 12s
hostnames-bvc05 1/1 Running 0 12s
hostnames-yp2kp 1/1 Running 0 12sThe astute reader will have noticed that we did not actually create a Service
yet - that is intentional. This is a step that sometimes gets forgotten, and
is the first thing to check.
So what would happen if I tried to access a non-existent Service? Assuming you
have another Pod that consumes this Service by name you would get something
like:
u@pod$ wget -qO- hostnames
wget: bad address 'hostname'or:
u@pod$ echo $HOSTNAMES_SERVICE_HOSTSo the first thing to check is whether that Service actually exists:
$ kubectl get svc hostnames
Error from server: service "hostnames" not foundSo we have a culprit, let's create the Service. As before, this is for the
walk-through - you can use your own Service's details here.
$ kubectl expose rc hostnames --port=80 --target-port=9376
NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE
hostnames 10.0.0.1 <none> 80/TCP run=hostnames 1hAnd read it back, just to be sure:
$ kubectl get svc hostnames
NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE
hostnames 10.0.0.1 <none> 80/TCP run=hostnames 1hAs before, this is the same as if you had started the Service with YAML:
apiVersion: v1
kind: Service
metadata:
name: hostnames
spec:
selector:
app: hostnames
ports:
- name: default
protocol: TCP
port: 80
targetPort: 9376Now you can confirm that the Service exists.
From a Pod in the same Namespace:
u@pod$ nslookup hostnames
Server: 10.0.0.10
Address: 10.0.0.10#53
Name: hostnames
Address: 10.0.1.175If this fails, perhaps your Pod and Service are in different
Namespaces, try a namespace-qualified name:
u@pod$ nslookup hostnames.default
Server: 10.0.0.10
Address: 10.0.0.10#53
Name: hostnames.default
Address: 10.0.1.175If this works, you'll need to ensure that Pods and Services run in the same
Namespace. If this still fails, try a fully-qualified name:
u@pod$ nslookup hostnames.default.svc.cluster.local
Server: 10.0.0.10
Address: 10.0.0.10#53
Name: hostnames.default.svc.cluster.local
Address: 10.0.1.175Note the suffix here: "default.svc.cluster.local". The "default" is the
Namespace we're operating in. The "svc" denotes that this is a Service.
The "cluster.local" is your cluster domain.
You can also try this from a Node in the cluster (note: 10.0.0.10 is my DNS
Service):
u@node$ nslookup hostnames.default.svc.cluster.local 10.0.0.10
Server: 10.0.0.10
Address: 10.0.0.10#53
Name: hostnames.default.svc.cluster.local
Address: 10.0.1.175If you are able to do a fully-qualified name lookup but not a relative one, you
need to check that your kubelet is running with the right flags.
The --cluster-dns flag needs to point to your DNS Service's IP and the
--cluster-domain flag needs to be your cluster's domain - we assumed
"cluster.local" in this document, but yours might be different, in which case
you should change that in all of the commands above.
If the above still fails - DNS lookups are not working for your Service - we
can take a step back and see what else is not working. The Kubernetes master
Service should always work:
u@pod$ nslookup kubernetes.default
Server: 10.0.0.10
Address 1: 10.0.0.10
Name: kubernetes
Address 1: 10.0.0.1If this fails, you might need to go to the kube-proxy section of this doc, or
even go back to the top of this document and start over, but instead of
debugging your own Service, debug DNS.
The next thing to test is whether your Service works at all. From a
Node in your cluster, access the Service's IP (from kubectl get above).
u@node$ curl 10.0.1.175:80
hostnames-0uton
u@node$ curl 10.0.1.175:80
hostnames-yp2kp
u@node$ curl 10.0.1.175:80
hostnames-bvc05If your Service is working, you should get correct responses. If not, there
are a number of things that could be going wrong. Read on.
It might sound silly, but you should really double and triple check that your
Service is correct and matches your Pods. Read back your Service and
verify it:
$ kubectl get service hostnames -o json
{
"kind": "Service",
"apiVersion": "v1",
"metadata": {
"name": "hostnames",
"namespace": "default",
"selfLink": "/api/v1/namespaces/default/services/hostnames",
"uid": "428c8b6c-24bc-11e5-936d-42010af0a9bc",
"resourceVersion": "347189",
"creationTimestamp": "2015-07-07T15:24:29Z",
"labels": {
"app": "hostnames"
}
},
"spec": {
"ports": [
{
"name": "default",
"protocol": "TCP",
"port": 80,
"targetPort": 9376,
"nodePort": 0
}
],
"selector": {
"app": "hostnames"
},
"clusterIP": "10.0.1.175",
"type": "ClusterIP",
"sessionAffinity": "None"
},
"status": {
"loadBalancer": {}
}
}Is the port you are trying to access in spec.ports[]? Is the targetPort
correct for your Pods? If you meant it to be a numeric port, is it a number
(9376) or a string "9376"? If you meant it to be a named port, do your Pods
expose a port with the same name? Is the port's protocol the same as the
Pod's?
If you got this far, we assume that you have confirmed that your Service
exists and resolves by DNS. Now let's check that the Pods you ran are
actually being selected by the Service.
Earlier we saw that the Pods were running. We can re-check that:
$ kubectl get pods -l app=hostnames
NAME READY STATUS RESTARTS AGE
hostnames-0uton 1/1 Running 0 1h
hostnames-bvc05 1/1 Running 0 1h
hostnames-yp2kp 1/1 Running 0 1hThe "AGE" column says that these Pods are about an hour old, which implies that
they are running fine and not crashing.
The -l app=hostnames argument is a label selector - just like our Service
has. Inside the Kubernetes system is a control loop which evaluates the
selector of every Service and save the results into an Endpoints object.
$ kubectl get endpoints hostnames
NAME ENDPOINTS
hostnames 10.244.0.5:9376,10.244.0.6:9376,10.244.0.7:9376This confirms that the control loop has found the correct Pods for your
Service. If the hostnames row is blank, you should check that the
spec.selector field of your Service actually selects for metadata.labels
values on your Pods.
At this point, we know that your Service exists and has selected your Pods.
Let's check that the Pods are actually working - we can bypass the Service
mechanism and go straight to the Pods.
u@pod$ wget -qO- 10.244.0.5:9376
hostnames-0uton
pod $ wget -qO- 10.244.0.6:9376
hostnames-bvc05
u@pod$ wget -qO- 10.244.0.7:9376
hostnames-yp2kpWe expect each Pod in the Endpoints list to return its own hostname. If
this is not what happens (or whatever the correct behavior is for your own
Pods), you should investigate what's happening there. You might find
kubectl logs to be useful or kubectl exec directly to your Pods and check
service from there.
If you get here, your Service is running, has Endpoints, and your Pods
are actually serving. At this point, the whole Service proxy mechanism is
suspect. Let's confirm it, piece by piece.
Confirm that kube-proxy is running on your Nodes. You should get something
like the below:
u@node$ ps auxw | grep kube-proxy
root 4194 0.4 0.1 101864 17696 ? Sl Jul04 25:43 /usr/local/bin/kube-proxy --master=https://kubernetes-master --kubeconfig=/var/lib/kube-proxy/kubeconfig --v=2Next, confirm that it is not failing something obvious, like contacting the
master. To do this, you'll have to look at the logs. Accessing the logs
depends on your Node OS. On some OSes it is a file, such as
/var/log/kube-proxy.log, while other OSes use journalctl to access logs. You
should see something like:
I0707 17:34:53.945651 30031 server.go:88] Running in resource-only container "/kube-proxy"
I0707 17:34:53.945921 30031 proxier.go:121] Setting proxy IP to 10.240.115.247 and initializing iptables
I0707 17:34:54.053023 30031 roundrobin.go:262] LoadBalancerRR: Setting endpoints for default/kubernetes: to [10.240.169.188:443]
I0707 17:34:54.053175 30031 roundrobin.go:262] LoadBalancerRR: Setting endpoints for default/hostnames:default to [10.244.0.5:9376 10.244.0.6:9376 10.244.0.7:9376]
I0707 17:34:54.053284 30031 roundrobin.go:262] LoadBalancerRR: Setting endpoints for default/kube-dns:dns to [10.244.3.3:53]
I0707 17:34:54.053310 30031 roundrobin.go:262] LoadBalancerRR: Setting endpoints for default/kube-dns:dns-tcp to [10.244.3.3:53]
I0707 17:34:54.054780 30031 proxier.go:306] Adding new service "default/kubernetes:" at 10.0.0.1:443/TCP
I0707 17:34:54.054903 30031 proxier.go:247] Proxying for service "default/kubernetes:" on TCP port 40074
I0707 17:34:54.079181 30031 proxier.go:306] Adding new service "default/hostnames:default" at 10.0.1.175:80/TCP
I0707 17:34:54.079273 30031 proxier.go:247] Proxying for service "default/hostnames:default" on TCP port 48577
I0707 17:34:54.113665 30031 proxier.go:306] Adding new service "default/kube-dns:dns" at 10.0.0.10:53/UDP
I0707 17:34:54.113776 30031 proxier.go:247] Proxying for service "default/kube-dns:dns" on UDP port 34149
I0707 17:34:54.120224 30031 proxier.go:306] Adding new service "default/kube-dns:dns-tcp" at 10.0.0.10:53/TCP
I0707 17:34:54.120297 30031 proxier.go:247] Proxying for service "default/kube-dns:dns-tcp" on TCP port 53476
I0707 17:34:54.902313 30031 proxysocket.go:130] Accepted TCP connection from 10.244.3.3:42670 to 10.244.3.1:40074
I0707 17:34:54.903107 30031 proxysocket.go:130] Accepted TCP connection from 10.244.3.3:42671 to 10.244.3.1:40074
I0707 17:35:46.015868 30031 proxysocket.go:246] New UDP connection from 10.244.3.2:57493
I0707 17:35:46.017061 30031 proxysocket.go:246] New UDP connection from 10.244.3.2:55471If you see error messages about not being able to contact the master, you
should double-check your Node configuration and installation steps.
One of the main responsibilities of kube-proxy is to write the iptables
rules which implement Services. Let's check that those rules are getting
written.
u@node$ iptables-save | grep hostnames
-A KUBE-PORTALS-CONTAINER -d 10.0.1.175/32 -p tcp -m comment --comment "default/hostnames:default" -m tcp --dport 80 -j REDIRECT --to-ports 48577
-A KUBE-PORTALS-HOST -d 10.0.1.175/32 -p tcp -m comment --comment "default/hostnames:default" -m tcp --dport 80 -j DNAT --to-destination 10.240.115.247:48577There should be 2 rules for each port on your Service (just one in this
example) - a "KUBE-PORTALS-CONTAINER" and a "KUBE-PORTALS-HOST". If you do
not see these, try restarting kube-proxy with the -V flag set to 4, and
then look at the logs again.
Assuming you do see the above rules, try again to access your Service by IP:
u@node$ curl 10.0.1.175:80
hostnames-0utonIf this fails, we can try accessing the proxy directly. Look back at the
iptables-save output above, and extract the port number that kube-proxy is
using for your Service. In the above examples it is "48577". Now connect to
that:
u@node$ curl localhost:48577
hostnames-yp2kpIf this still fails, look at the kube-proxy logs for specific lines like:
Setting endpoints for default/hostnames:default to [10.244.0.5:9376 10.244.0.6:9376 10.244.0.7:9376]If you don't see those, try restarting kube-proxy with the -V flag set to 4, and
then look at the logs again.
If you get this far, something very strange is happening. Your Service is
running, has Endpoints, and your Pods are actually serving. You have DNS
working, iptables rules installed, and kube-proxy does not seem to be
misbehaving. And yet your Service is not working. You should probably let
us know, so we can help investigate!
Contact us on IRC or email or GitHub.
Visit troubleshooting document for more information.