On this post I have added some quick Kubectl commands to get started with Kubernetes
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” create deployment hello-node –image=gcr.io/hello-minikube-zero-install/hello-node
deployment.apps/hello-node created
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” get all
NAME READY STATUS RESTARTS AGE
pod/hello-node-55b49fb9f8-c9xx5 1/1 Running 0 53s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.245.0.1 <none> 443/TCP 115d
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/hello-node 1/1 1 1 56s
NAME DESIRED CURRENT READY AGE
replicaset.apps/hello-node-55b49fb9f8 1 1 1 55s
Newyork:.kube esumit$
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” get events
LAST SEEN TYPE REASON OBJECT MESSAGE
3m5s Normal Scheduled pod/hello-node-55b49fb9f8-c9xx5 Successfully assigned default/hello-node-55b49fb9f8-c9xx5 to fccollect-bnx8
3m3s Normal Pulling pod/hello-node-55b49fb9f8-c9xx5 Pulling image “gcr.io/hello-minikube-zero-install/hello-node”
2m36s Normal Pulled pod/hello-node-55b49fb9f8-c9xx5 Successfully pulled image “gcr.io/hello-minikube-zero-install/hello-node”
2m36s Normal Created pod/hello-node-55b49fb9f8-c9xx5 Created container hello-node
2m35s Normal Started pod/hello-node-55b49fb9f8-c9xx5 Started container hello-node
3m5s Normal SuccessfulCreate replicaset/hello-node-55b49fb9f8 Created pod: hello-node-55b49fb9f8-c9xx5
3m5s Normal ScalingReplicaSet deployment/hello-node Scaled up replica set hello-node-55b49fb9f8 to 1
Newyork:.kube esumit$
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” expose deployment hello-node –type=LoadBalancer –port=8080
service/hello-node exposed
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” get services
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
hello-node LoadBalancer 10.245.120.20 159.65.211.207 8080:31568/TCP 105s
kubernetes ClusterIP 10.245.0.1 <none> 443/TCP 115d
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” get pods
NAME READY STATUS RESTARTS AGE
hello-node-55b49fb9f8-c9xx5 1/1 Running 0 26m
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” describe hello-node-55b49fb9f8-c9xx5
error: the server doesn’t have a resource type “hello-node-55b49fb9f8-c9xx5”
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” describe pod hello-node-55b49fb9f8-c9xx5
Name: hello-node-55b49fb9f8-c9xx5
Namespace: default
Priority: 0
Node: fccollect-bnx8/10.131.235.122
Start Time: Thu, 26 Dec 2019 20:11:05 +1000
Labels: app=hello-node
pod-template-hash=55b49fb9f8
Annotations: <none>
Status: Running
IP: 10.244.0.249
Controlled By: ReplicaSet/hello-node-55b49fb9f8
Containers:
hello-node:
Container ID: docker://26108e00ae2983c191211e6d754b251c613618bdf7c9d9d36f1f1fac466054f4
Image: gcr.io/hello-minikube-zero-install/hello-node
Image ID: docker-pullable://gcr.io/hello-minikube-zero-install/hello-node@sha256:9cf82733f7278ae7ae899d432f8d3b3bb0fcb54e673c67496a9f76bb58f30a1c
Port: <none>
Host Port: <none>
State: Running
Started: Thu, 26 Dec 2019 20:11:35 +1000
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-gf5v2 (ro)
Conditions:
Type Status
Initialized True
Ready True
ContainersReady True
PodScheduled True
Volumes:
default-token-gf5v2:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-gf5v2
Optional: false
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
node.kubernetes.io/unreachable:NoExecute for 300s
Events:
Type Reason Age From Message
—- —— —- —- ——-
Normal Scheduled 27m default-scheduler Successfully assigned default/hello-node-55b49fb9f8-c9xx5 to fccollect-bnx8
Normal Pulling 27m kubelet, fccollect-bnx8 Pulling image “gcr.io/hello-minikube-zero-install/hello-node”
Normal Pulled 27m kubelet, fccollect-bnx8 Successfully pulled image “gcr.io/hello-minikube-zero-install/hello-node”
Normal Created 27m kubelet, fccollect-bnx8 Created container hello-node
Normal Started 27m kubelet, fccollect-bnx8 Started container hello-node
Newyork:.kube esumit$
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” cluster-info
Kubernetes master is running at https://91a32bee-1c2d-4fa8-8ade-1d2e5329645a.k8s.ondigitalocean.com
CoreDNS is running at https://91a32bee-1c2d-4fa8-8ade-1d2e5329645a.k8s.ondigitalocean.com/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
To further debug and diagnose cluster problems, use ‘kubectl cluster-info dump’.
Newyork:.kube esumit$
Newyork:.kube esumit$ kubectl –kubeconfig=”k8-fccollect.yaml” api-versions
admissionregistration.k8s.io/v1beta1
apiextensions.k8s.io/v1beta1
apiregistration.k8s.io/v1
apiregistration.k8s.io/v1beta1
apps/v1
apps/v1beta1
apps/v1beta2
authentication.k8s.io/v1
authentication.k8s.io/v1beta1
authorization.k8s.io/v1
authorization.k8s.io/v1beta1
autoscaling/v1
autoscaling/v2beta1
autoscaling/v2beta2
batch/v1
batch/v1beta1
certificates.k8s.io/v1beta1
cilium.io/v2
coordination.k8s.io/v1
coordination.k8s.io/v1beta1
events.k8s.io/v1beta1
extensions/v1beta1
networking.k8s.io/v1
networking.k8s.io/v1beta1
node.k8s.io/v1beta1
policy/v1beta1
rbac.authorization.k8s.io/v1
rbac.authorization.k8s.io/v1beta1
scheduling.k8s.io/v1
scheduling.k8s.io/v1beta1
snapshot.storage.k8s.io/v1alpha1
storage.k8s.io/v1
storage.k8s.io/v1beta1
v1
Newyork:.kube esumit$
cat k8sexperiment-kubeconfig-latest.yaml
504 kubectl –kubeconfig=”k8sexperiment-kubeconfig-latest.yaml” get nodes
505 kubectl –kubeconfig=”k8sexperiment-kubeconfig-latest.yaml” get nodes
506 cd ~/.kube/
507 ls
508 kubectl –kubeconfig=”k8s-fccollect-kubeconfig.yaml” get nodes
509 kubectl get nodes
510 cat k8s-fccollect-kubeconfig.yaml
511 ls
512 ls
513 sudo vi k8s-fccollect-kubeconfig.yaml
514 sudo vi k8-fccollect.yaml
515 kubectl –kubeconfig=”k8-fccollect.yaml” get nodes
516 kubectl help
517 kubectl api-versions
518 kubectl –kubeconfig=”k8-fccollect.yaml” api-versions
519 kubectl –kubeconfig=”k8-fccollect.yaml” cluster-info
520 kubectl –kubeconfig=”k8-fccollect.yaml” api-resources
521 kubectl –kubeconfig=”k8-fccollect.yaml” get-clusters
522 kubectl –kubeconfig=”k8-fccollect.yaml” get-clusters
523 kubectl –kubeconfig=”k8-fccollect.yaml” get-contexts
524 kubectl –kubeconfig=”k8-fccollect.yaml” get
525 kubectl –kubeconfig=”k8-fccollect.yaml” explain
526 kubectl –kubeconfig=”k8-fccollect.yaml” nodesexplain
527 kubectl –kubeconfig=”k8-fccollect.yaml” nodes explain
528 kubectl –kubeconfig=”k8-fccollect.yaml” version
529 kubectl –kubeconfig=”k8-fccollect.yaml” get pods
530 kubectl –kubeconfig=”k8-fccollect.yaml” current-context
531 kubectl –kubeconfig=”k8-fccollect.yaml” create deployment hello-node –image=gcr.io/hello-minikube-zero-install/hello-node
532 kubectl –kubeconfig=”k8-fccollect.yaml” get all
533 kubectl –kubeconfig=”k8-fccollect.yaml” get events
534 kubectl –kubeconfig=”k8-fccollect.yaml” expose deployment hello-node –type=LoadBalancer –port=8080
535 kubectl –kubeconfig=”k8-fccollect.yaml” get services
536 kubectl –kubeconfig=”k8-fccollect.yaml” get pods
537 kubectl –kubeconfig=”k8-fccollect.yaml” describe hello-node-55b49fb9f8-c9xx5
538 kubectl –kubeconfig=”k8-fccollect.yaml” describe pod hello-node-55b49fb9f8-c9xx5
539 pwd
540 cd ~
541 ls
542 cd Documents/
543 ls
544 mkdir k8s
545 cd k8s
546 sudo vi busybox.yaml
547 kubectl –kubeconfig=”k8-fccollect.yaml” create -f busybox.yaml
548 ls
549 cp ~/.kube/k8-fccollect.yaml .
550 kubectl –kubeconfig=”k8-fccollect.yaml” create -f busybox.yaml
551 sudo vi busybox.yaml
552 kubectl –kubeconfig=”k8-fccollect.yaml” create -f busybox.yaml
553 kubectl –kubeconfig=”k8-fccollect.yaml” get s
554 kubectl –kubeconfig=”k8-fccollect.yaml” get s [TAB]
555 history
Newyork:k8s esumit$
https://stackoverflow.com/questions/50838141/how-can-we-create-service-dependencies-using-kubernetes
https://stackoverflow.com/questions/49368047/what-is-the-equivalent-for-depends-on-in-kubernetes
Typically you don’t; you just let Helm (or kubectl apply -f) start everything in one shot and let it retry starting everything.
The most common pattern is for a container process to simply crash at startup if an external service isn’t available; the Kubernetes Pod mechanism will restart the container when this happens. If the dependency never comes up you’ll be stuck in CrashLoopBackOff state forever, but if it appears in 5-10 seconds then everything will come up normally within a minute or two.
Also remember that pods of any sort are fairly disposable in Kubernetes. IME if something isn’t working in a service one of the first things to try is kubectl delete pod and letting a Deployment controller recreate it. Kubernetes can do this on its own too, for example if it decides it needs to relocate a pod on to a different node. That is: even if some dependency is up when your pod first start sup, there’s no guarantee it will stay up forever.
Pods communication across nodes
If the services are in the same namespace you can use http://servicename:port
If they are indifferent namespaces then you can use FQDN http://servicename.namespace.svc.cluster.local:port
By default, pods can communicate with each other by their IP address, regardless of the namespace they’re in.
You can see the IP address of each pod with:
kubectl get pods -o wide --all-namespaces
However, the normal way to communicate within a cluster is through Service resources.
https://stackoverflow.com/questions/45720084/how-to-make-two-kubernetes-services-talk-to-each-other
A Service also has an IP address and additionally a DNS name. A Service is backed by a set of pods. The Service forwards requests to itself to one of the backing pods.
The fully qualified DNS name of a Service is:
<service-name>.<service-namespace>.svc.cluster.local
This can be resolved to the IP address of the Service from anywhere in the cluster (regardless of namespace).
For example, if you have:
- Namespace
ns-a: Servicesvc-a→ set of pods A - Namespace
ns-b: Servicesvc-b→ set of pods B
Then a pod of set A can reach a pod of set B by making a request to:
svc-b.ns-b.svc.cluster.local
Sumit Arora 