Use Port Forwarding to Access Applications in a Cluster (使用端口转发访问集群里的应用)#

原文

This page shows how to use kubectl port-forward to connect to a MongoDB server running in a Kubernetes cluster. This type of connection can be useful for database debugging.

这个页面展示了如何使用 kubectl port-forward 连接k8s集群中一个正在运行的MongoDB服务端。这种类型的连接对数据库调试很有用。

Before you begin#

todo

Creating MongoDB deployment and service (创建一个MongoDB deployment和service)#

1. Create a Deployment that runs MongoDB:

   kubectl apply -f https://k8s.io/examples/application/mongodb/mongo-deployment.yaml

   The output of a successful command verifies that the deployment was created:

   deployment.apps/mongo created

   View the pod status to check that it is ready:

   kubectl get pods

   The output displays the pod created:

   NAME READY STATUS RESTARTS AGE mongo-75f59d57f4-4nd6q 1/1 Running 0 2m4s

   View the Deployment's status:

   kubectl get deployment

   The output displays that the Deployment was created:

   NAME READY UP-TO-DATE AVAILABLE AGE mongo 1/1 1 1 2m21s

   The Deployment automatically manages a ReplicaSet. View the ReplicaSet status using:

   kubectl get replicaset

   The output displays that the ReplicaSet was created:

   NAME DESIRED CURRENT READY AGE mongo-75f59d57f4 1 1 1 3m12s

2. Create a Service to expose MongoDB on the network:

   kubectl apply -f https://k8s.io/examples/application/mongodb/mongo-service.yaml

   The output of a successful command verifies that the Service was created:

   service/mongo created

   Check the Service created:

   kubectl get service mongo

   The output displays the service created:

   NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE mongo ClusterIP 10.96.41.183 <none> 27017/TCP 11s

3. Verify that the MongoDB server is running in the Pod, and listening on port 27017:

   # Change mongo-75f59d57f4-4nd6q to the name of the Pod
   kubectl get pod mongo-75f59d57f4-4nd6q --template='{{(index (index .spec.containers 0).ports 0).containerPort}}{{"\n"}}'

   The output displays the port for MongoDB in that Pod:

   27017

   27017 is the official TCP port for MongoDB.

Forward a local port to a port on the Pod#

1. kubectl port-forward allows using resource name, such as a pod name, to select a matching pod to port forward to.

   # Change mongo-75f59d57f4-4nd6q to the name of the Pod
   kubectl port-forward mongo-75f59d57f4-4nd6q 28015:27017

   which is the same as

   kubectl port-forward pods/mongo-75f59d57f4-4nd6q 28015:27017

   or

   kubectl port-forward deployment/mongo 28015:27017

   or

   kubectl port-forward replicaset/mongo-75f59d57f4 28015:27017

   or

   kubectl port-forward service/mongo 28015:27017

   Any of the above commands works. The output is similar to this:

   Forwarding from 127.0.0.1:28015 -> 27017 Forwarding from [::1]:28015 -> 27017

   {{< note >}} kubectl port-forward does not return. To continue with the exercises, you will need to open another terminal. {{< /note >}}

2. Start the MongoDB command line interface:

   mongosh --port 28015

3. At the MongoDB command line prompt, enter the ping command:

   db.runCommand( { ping: 1 } )

   A successful ping request returns:

   { ok: 1 }

Optionally let kubectl choose the local port#

If you don't need a specific local port, you can let kubectl choose and allocate the local port and thus relieve you from having to manage local port conflicts, with the slightly simpler syntax:

kubectl port-forward deployment/mongo :27017

The kubectl tool finds a local port number that is not in use (avoiding low ports numbers, because these might be used by other applications). The output is similar to:

Discussion#

Connections made to local port 28015 are forwarded to port 27017 of the Pod that is running the MongoDB server. With this connection in place, you can use your local workstation to debug the database that is running in the Pod.

{{< note >}} kubectl port-forward is implemented for TCP ports only. The support for UDP protocol is tracked in issue 47862. {{< /note >}}

{{% heading "whatsnext" %}}#

Learn more about kubectl port-forward.