update hostport doc

2017-10-17 10:11:59 +08:00
parent 47a377a688
commit 05af66ef77
1 changed files with 3 additions and 1 deletions
@@ -45,7 +45,9 @@ This is a living document. If you think of something that is not on this list bu
    2. Create a service;
    3. Then scale up the replication controller.

- Don't use `hostPort` unless it is absolutely necessary (for example: for a node daemon). It specifies the port number to expose on the host. When you bind a Pod to a `hostPort`, there are a limited number of places to schedule a pod due to port conflicts— you can only schedule as many such Pods as there are nodes in your Kubernetes cluster.
+- Don't use `hostPort` unless it is absolutely necessary (for example: for a node daemon). It specifies the port number to expose on the host.  When you bind a Pod to a `hostPort`, there are a limited number of places to schedule a pod due to port conflicts. The conflict comes from being limited to a single `hostIP:hostPort:protocol` combination. Different `hostIP:hostPort:protocol` combinations mean different requirements. For example, a pod that binds tcp 80 host port on 127.0.0.1 does not conflict with another pod that binds tcp 80 port on 127.0.0.2. 
+  
+  Special notes on hostIP and protocol, if you don't specify the hostIP and protocol explicitly, kubernetes will give you 0.0.0.0 and tcp as default hostIP and protocol. And "0.0.0.0" is a wildcard hostIP that will occupy all <_,hostPort,protocol> on the node the pod is scheduled on. Specifically, it will occupy all <IP,hostPort,protocol> for all IPs on the host.

  If you only need access to the port for debugging purposes, you can use the [kubectl proxy and apiserver proxy](/docs/tasks/access-kubernetes-api/http-proxy-access-api/) or [kubectl port-forward](/docs/tasks/access-application-cluster/port-forward-access-application-cluster/).
  You can use a [Service](/docs/concepts/services-networking/service/) object for external service access.