145 lines
4.4 KiB
Markdown
145 lines
4.4 KiB
Markdown
---
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title: Using a Service to Access an Application in a Cluster
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---
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{% capture overview %}
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This page shows how to create a Kubernetes Service object that external
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clients can use to access an application running in a cluster. The Service
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provides load balancing for an application that has two running instances.
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{% endcapture %}
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{% capture prerequisites %}
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{% include task-tutorial-prereqs.md %}
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{% endcapture %}
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{% capture objectives %}
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* Run two instances of a Hello World application.
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* Create a Service object that exposes a node port.
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* Use the Service object to access the running application.
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{% endcapture %}
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{% capture lessoncontent %}
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### Creating a service for an application running in two pods
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1. Run a Hello World application in your cluster:
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kubectl run hello-world --replicas=2 --labels="run=load-balancer-example" --image=gcr.io/google-samples/node-hello:1.0 --port=8080
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The preceding command creates a
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[Deployment](/docs/user-guide/deployments/)
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object and an associated
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[ReplicaSet](/docs/user-guide/replicasets/)
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object. The ReplicaSet has two
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[Pods](/docs/user-guide/pods/),
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each of which runs the Hello World application.
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1. Display information about the Deployment:
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kubectl get deployments hello-world
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kubectl describe deployments hello-world
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1. Display information about your ReplicaSet objects:
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kubectl get replicasets
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kubectl describe replicasets
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1. Create a Service object that exposes the deployment:
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kubectl expose deployment hello-world --type=NodePort --name=example-service
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1. Display information about the Service:
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kubectl describe services example-service
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The output is similar to this:
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Name: example-service
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Namespace: default
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Labels: run=load-balancer-example
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Selector: run=load-balancer-example
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Type: NodePort
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IP: 10.32.0.16
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Port: <unset> 8080/TCP
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NodePort: <unset> 31496/TCP
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Endpoints: 10.200.1.4:8080,10.200.2.5:8080
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Session Affinity: None
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No events.
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Make a note of the NodePort value for the service. For example,
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in the preceding output, the NodePort value is 31496.
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1. List the pods that are running the Hello World application:
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kubectl get pods --selector="run=load-balancer-example" --output=wide
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The output is similar to this:
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NAME READY STATUS ... IP NODE
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hello-world-2895499144-bsbk5 1/1 Running ... 10.200.1.4 worker1
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hello-world-2895499144-m1pwt 1/1 Running ... 10.200.2.5 worker2
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1. Get the public IP address of one of your nodes that is running
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a Hello World pod. How you get this address depends on how you set
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up your cluster. For example, if you are using Minikube, you can
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see the node address by running `kubectl cluster-info`. If you are
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using Google Compute Engine instances, you can use the
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`gcloud compute instances list` command to see the public addresses of your
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nodes.
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1. On your chosen node, create a firewall rule that allows TCP traffic
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on your node port. For example, if your Service has a NodePort value of
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31568, create a firewall rule that allows TCP traffic on port 31568.
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1. Use the node address and node port to access the Hello World application:
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curl http://<public-node-ip>:<node-port>
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where `<public-node-ip>` is the public IP address of your node,
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and `<node-port>` is the NodePort value for your service.
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The response to a successful request is a hello message:
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Hello Kubernetes!
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### Using a service configuration file
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As an alternative to using `kubectl expose`, you can use a
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[service configuration file](/docs/user-guide/services/operations)
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to create a Service.
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{% endcapture %}
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{% capture cleanup %}
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To delete the Service, enter this command:
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kubectl delete services example-service
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To delete the Deployment, the ReplicaSet, and the Pods that are running
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the Hello World application, enter this command:
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kubectl delete deployment hello-world
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{% endcapture %}
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{% capture whatsnext %}
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Learn more about
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[connecting applications with services](/docs/user-guide/connecting-applications/).
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{% endcapture %}
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{% include templates/tutorial.md %}
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