从 pod minikube kubernetes 中的容器公开端口

Question

I'm new to K8s, I'll try minikube with 2 container running in a pod with this command:

kubectl apply -f deployment.yaml

and this deployment.yml:

 apiVersion: v1 kind: Pod metadata: name: site-home spec: restartPolicy: Never volumes: - name: v-site-home emptyDir: {} containers: - name: site-web image: site-home:1.0.0 ports: - containerPort: 80 volumeMounts: - name: v-site-home mountPath: /usr/share/nginx/html/assets/quotaLago - name: site-cron image: site-home-cron:1.0.0 volumeMounts: - name: v-site-home mountPath: /app/quotaLago

I've a shared volume so if I understand I cannot use deployment but only pods (maybe stateful set?)

In any case I want to expose the port 80 from the container site-web in the pod site-home. In the official docs I see this for deployments:

kubectl expose deployment hello-node --type=LoadBalancer --port=8080

but I cannot use for example:

kubectl expose pod site-web --type=LoadBalancer --port=8080

any idea?

Answer 1

but I cannot use for example:

 kubectl expose pod site-web --type=LoadBalancer --port=8080

Of course you can, however exposing a single Pod via LoadBalancer Service doesn't make much sense. If you have a Deployment which typically manages a set of Pods between which the real load can be balanced, LoadBalancer does its job. However you can still use it just for exposing a single Pod .

Note that your container exposes port 80 , not 8080 ( containerPort: 80 in your container specification) so you need to specify it as target-port in your Service . Your kubectl expose command may look like this:

kubectl expose pod site-web --type=LoadBalancer --port=8080 --target-port=80

If you provide only --port=8080 flag to your kubectl expose command it assumes that the target-port 's value is the same as value of --port . You can easily check it by yourself looking at the service you've just created:

kubectl get svc site-web -o yaml

and you'll see something like this in spec.ports section:

- nodePort: 32576
    port: 8080
    protocol: TCP
    targetPort: 8080

After exposing your Pod (or Deployment ) properly ie using:

kubectl expose pod site-web --type=LoadBalancer --port=8080 --target-port=80

you'll see something similar:

  - nodePort: 31181
    port: 8080
    protocol: TCP
    targetPort: 80

After issuing kubectl get services you should see similar output:

NAME                            TYPE           CLUSTER-IP    EXTERNAL-IP      PORT(S)          AGE
site-web                              ClusterIP      <Cluster IP>   <External IP>           8080:31188/TCP         4m42s

If then you go to http://<External IP>:8080 in your browser or run curl http://<External IP>:8080 you should see your website's frontend.

Keep in mind that this solution makes sense and will be fully functional in cloud environment which is able to provide you with a real load balancer. Note that if you declare such Service type in Minikukbe in fact it creates NodePort service as it is unable to provide you with a real load balancer. So your application will be available on your Node's ( your Minikube VM's ) IP address on randomly selected port in range 30000-32767 (in my example it's port 31181 ).

As to your question about the volume:

I've a shared volume so if I understand I cannot use deployment but only pods (maybe stateful set?)

yes, if you want to use specifically EmptyDir volume, it cannot be shared between different Pods (even if they were scheduled on the same node), it is shared only between containers within the same Pod . If you want to use Deployment you'll need to think about another storage solution such asPersistenetVolume .

---

EDIT:

In the first moment I didn't notice the error in your command:

kubectl expose pod site-web --type=LoadBalancer --port=8080

You're trying to expose non-existing Pod as your Pod 's name is site-home , not site-web . site-web is a name of one of your containers (within your site-home Pod ). Remember: we're exposing Pod , not containers via Service .

I change 80->8080 but I always come to error:kubectl expose pod site-home --type=LoadBalancer --port=8080 return:error: couldn't retrieve selectors via --selector flag or introspection: the pod has no labels and cannot be exposed See 'kubectl expose -h' for help and examples.

The key point here is: the pod has no labels and cannot be exposed

It looks like your Pod doesn't have any labels defined which are required so that the Service can select this particular Pod (or set of similar Pods which have the same label) from among other Pods in your cluster. You need at least one label in your Pod definition. Adding simple label name: site-web under Pod 's metadata section should help. It may look like this in your Pod definition:

apiVersion: v1
kind: Pod
metadata:
  name: site-home
  labels:
    name: site-web
spec:
...

Now you may even provide this label as selector in your service however it should be handled automatically if you omit --selector flag:

kubectl expose pod site-home --type=LoadBalancer --port=8080 --target-port=80 --selector=name=site-web

Remember: in Minikube real load balancer cannot be created and instead of LoadBalancer NodePort type will be created. Command kubectl get svc will tell you on which port (in range 30000-32767 ) your application will be available.

and `kubectl expose pod site-web --type=LoadBalancer --port=8080 return: Error from server (NotFound): pods "site-web" not found. Site-home is the pod, site-web is the container with the port exposed, what's the issue?

if you don't have a Pod with name "site-web" you can expect such message. Here you are simply trying to expose non-existing Pod .

If I exposed a port from a container the port is automatically exposed also for the pod?

Yes, you have the port defined in Container definition. Your Pods automatically expose all ports that are exposed by the Containers within them.