How to access pods without services in Kubernetes

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I was wondering how pods are accessed when no service is defined for that specific pod. If it's through the environment variables, how does the cluster retrieve these?

Also, when services are defined, where on the master node is it stored?

Kind regards, Charles

Access Services Running on Clusters, In Kubernetes, nodes, pods and services all have their own IPs. In many cases, the node IPs, pod IPs, and some service IPs on a cluster will not be routable,  To access one specific pod from a set of replicas, such as for debugging, place a unique label on the pod and create a new service which selects this label. In most cases, it should not be necessary for application developer to directly access nodes via their nodeIPs.

You cannot "access" a pods container port(s) without a service. Services are objects that define the desired state of an ultimate set of iptable rule(s).

Also, services, like all other objects, are stored in etcd and maintained through your master(s).

You could however manually create an iptable rule forwarding traffic to the local container port that docker has exposed.

Hope this helps! If you still have any questions drop them here.

Using a Service to Expose Your App, Objectives Learn about a Service in Kubernetes Understand how labels and which defines a logical set of Pods and a policy by which to access them. Although each Pod has a unique IP address, those IPs are not  By default Kubernetes services are accessible at the ClusterIP which is an internal IP address reachable from inside of the Kubernetes cluster only. The ClusterIP enables the applications running within the pods to access the service. To make the service accessible from outside of the cluster a user can create a service of type NodePort.

Connecting Applications with Services, If you do not already have a cluster, you can create one by using Minikube, or you the Pods that are running the Hello World application, enter this command: Public access to a Service through Ingress: This is the right method to publish an application, defined through a Service in Kubernetes, for access by everybody. Authenticated access to a Pod through kubectl port-forward : This gives you direct network access to a port of a Pod, for test purposes.

Just for debugging purposes, you can forward a port from your machine to one in the pod:

kubectl port-forward POD_NAME HOST_PORT:POD_PORT

If you have to access it from anywhere, you should use services, but you got to have a deployment created

Create deployment

kubectl create -f https://raw.githubusercontent.com/kubernetes/website/master/content/en/examples/service/networking/run-my-nginx.yaml

Expose the deployment with a NodePort service

kubectl expose deployment deployment/my-nginx --type=NodePort --name=nginx-service

Then list the services and get the port of the service

kubectl get services | grep nginx-service

Use a Service to Access an Application in a Cluster, Containers in different Pods have distinct IP addresses and can not of multiple cooperating processes which form a cohesive unit of service. Linux capabilities like manipulating the network stack and accessing devices. Also, you cannot count on a Pod getting the same IP after a restart - how will a client application continue to access the Pod? Enter Kubernetes Services! Kubernetes Service A Service is a higher level component that provides access to a bunch of Pods. It decouples the client application from the specifics of a Deployment (or a set of Pods in

Pods, Services without selectors. Services most commonly abstract access to Kubernetes Pods, but they can also abstract other kinds of backends. A Kubernetes service is a building block that defines a logical set of pods and a policy to access those pods. Similar to a replication controller, a service uses a label selector to define a set of managed pods, and the pods in that set should have the corresponding label.

Service, service/load-balancer-example.yaml which is not covered in this example, please refer to this page To verify these are pod addresses, enter this command: To access one specific pod from a set of replicas, such as for debugging, place a unique label on the pod and create a new service which selects this label. In most cases, it should not be necessary for application developer to directly access nodes via their nodeIPs.

Exposing an External IP Address to Access an , Access services, nodes, or pods using the Proxy Use this if the services are not secure enough to  Kubernetes gives every pod its own cluster-private IP address, so you do not need to explicitly create links between pods or map container ports to host ports. This means that containers within a Pod can all reach each other's ports on localhost, and all pods in a cluster can see each other without NAT.

Comments
  • Have you looked into kubernetes documentation and maybe got some clues?
  • I thought Kubernetes DNS was an optional feature? Are you saying that you need DNS if you are accessing services from outside the cluster?
  • DNS is optional for highly recommended way of doing it
  • ENV vars vs DNS discussion is in the context of when your pod want to access a service from other pod
  • The kubernetes service object uses labels and iptables rules
  • I understand. but how does one pod know the port and IP from another pod? Does it make a request to the master that it wants to reach a certain pod, who then answers with the right ENV vars to the calling pod?
  • Okay, I understand that services are necessary for access from outside the cluster and stored in the etcd in the master node. Imagine that pod 1 on node A, wants to access a functionality provided by pod 2 on node B. How does pod 1 know how to reach pod 2, if there are no services?
  • Does the cluster store a backup of the etcd somewhere?
  • @CharlesVanDamme It is a distributed etcd store. Typically, all distributed systems store multiple copies in a cluster of machines