Skip to content

Latest commit

 

History

History
537 lines (420 loc) · 17.1 KB

debugging-services.md

File metadata and controls

537 lines (420 loc) · 17.1 KB
Raw

My Service is not working - how to debug

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

Conventions

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
OUTPUT

If the command "COMMAND" is expected to run on a Node and produce "OUTPUT":

u@node$ COMMAND
OUTPUT

If the command is "kubectl ARGS":

$ kubectl ARGS
OUTPUT

Running commands in a Pod

For 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-sleep

Now, 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
/ #

Setup

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   3

Note 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: TCP

Confirm 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          12s

Does the Service exist?

The 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_HOST

So the first thing to check is whether that Service actually exists:

$ kubectl get svc hostnames
Error from server: service "hostnames" not found

So 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        LABELS          SELECTOR        IP(S)     PORT(S)
hostnames   app=hostnames   app=hostnames             80/TCP

And read it back, just to be sure:

$ kubectl get svc hostnames
NAME        LABELS          SELECTOR        IP(S)        PORT(S)
hostnames   app=hostnames   app=hostnames   10.0.1.175   80/TCP

As 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: 9376

Now you can confirm that the Service exists.

Does the Service work by DNS?

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: 10.0.1.175

If 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: 10.0.1.175

If 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: 10.0.1.175

Note 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: 10.0.1.175

If 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.

Does any Service exist in DNS?

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: 10.0.0.1

If 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.

Does the Service work by IP?

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-bvc05

If your Service is working, you should get correct responses. If not, there are a number of things that could be going wrong. Read on.

Is the Service correct?

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?

Does the Service have any Endpoints?

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          1h

The "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   10.244.0.5:9376,10.244.0.6:9376,10.244.0.7:9376

This 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.

Are the Pods working?

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-yp2kp

We 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.

Is the kube-proxy working?

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.

Is kube-proxy running?

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=2

Next, 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 10.244.3.2:55471

If you see error messages about not being able to contact the master, you should double-check your Node configuration and installation steps.

Is kube-proxy writing iptables rules?

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 10.240.115.247:48577

There 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.

Is kube-proxy proxying?

Assuming you do see the above rules, try again to access your Service by IP:

u@node$ curl 10.0.1.175:80
hostnames-0uton

If 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-yp2kp

If 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.

Seek help

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.

More information

Visit troubleshooting document for more information.

Analytics