diff --git a/docs/node.md b/docs/node.md index 99cdeb3bb29..12377794ecb 100644 --- a/docs/node.md +++ b/docs/node.md @@ -2,7 +2,7 @@ ## What is a node? -`Node` is a worker node in Kubernetes, previously known as `Minion`. Node +`Node` is a worker machine in Kubernetes, previously known as `Minion`. Node may be a VM or physical machine, depending on the cluster. Each node has the services necessary to run [Pods](pods.md) and be managed from the master systems. The services include docker, kubelet and network proxy. See @@ -11,11 +11,13 @@ doc for more details. ## Node Status -Node status describes current status of a node. For now, there are three +Node status describes current status of a node. For now, there are the following pieces of information: -### HostIP +### Node Addresses + Host IP address is queried from cloudprovider and stored as part of node status. If kubernetes runs without cloudprovider, node's ID will be used. IP address can change, and there are different kind of IPs, e.g. public @@ -37,11 +39,12 @@ scheduling Pods. For a node to be considered a scheduling candidate, it must have appropriate conditions, see below. ### Node Condition -Node Condition describes the conditions of `Running` nodes. Current valid -condition is `NodeReady`. In the future, we plan to add more. -`NodeReady` means kubelet is healthy and ready to accept pods. Different -condition provides different level of understanding for node health. -Node condition is represented as a json object. For example, +Node Condition describes the conditions of `Running` nodes. (However, +it can be present also when node status is different, e.g. `Unknown`) +Current valid condition is `Ready`. In the future, we plan to add more. +`Ready` means kubelet is healthy and ready to accept pods. Different +condition provides different level of understanding for node health. +Node condition is represented as a json object. For example, the following conditions mean the node is in sane state: ```json "conditions": [ @@ -52,9 +55,20 @@ the following conditions mean the node is in sane state: ] ``` +### Node Capacity + +Describes the resources available on the node: CPUs, memory and the maximum +number of pods that can be scheduled on this node. + +### Node Info +General information about the node, for instance kernel version, kubernetes +version, docker version (if used), OS name. The information is gathered by +Kubernetes from the node. + + ## Node Management -Unlike [Pod](pods.md) and [Service](services.md), `Node` is not inherently +Unlike [Pods](pods.md) and [Services](services.md), a Node is not inherently created by Kubernetes: it is either created from cloud providers like GCE, or from your physical or virtual machines. What this means is that when Kubernetes creates a node, it only creates a representation for the node. @@ -73,10 +87,10 @@ For example, if you try to create a node from the following content: } ``` -Kubernetes will create a `Node` object internally (the representation), and +Kubernetes will create a Node object internally (the representation), and validate the node by health checking based on the `metadata.name` field: we assume `metadata.name` can be resolved. If the node is valid, i.e. all necessary -services are running, it is eligible to run a `Pod`; otherwise, it will be +services are running, it is eligible to run a Pod; otherwise, it will be ignored for any cluster activity, until it becomes valid. Note that Kubernetes will keep invalid node unless explicitly deleted by client, and it will keep checking to see if it becomes valid. @@ -86,13 +100,13 @@ Node Controller and Kube Admin. ### Node Controller -Node controller is a component in Kubernetes master which manages `Node` +Node controller is a component in Kubernetes master which manages Node objects. It performs two major functions: cluster-wide node synchronization and single node life-cycle management. -Node controller has a sync loop that creates/deletes `Node`s from Kubernetes +Node controller has a sync loop that creates/deletes Nodes from Kubernetes based on all matching VM instances listed from cloud provider. The sync period -can be controlled via flag "--node_sync_period". If a new instance +can be controlled via flag `--node_sync_period`. If a new instance gets created, Node Controller creates a representation for it. If an existing instance gets deleted, Node Controller deletes the representation. Note however, Node Controller is unable to provision the node for you, i.e. it won't install @@ -108,7 +122,7 @@ register itself with the API server. This is the preferred pattern, used by mos For self-registration, the kubelet is started with the following options: - `--apiservers=` tells the kubelet the location of the apiserver. - - `--kubeconfig` tells kubelet where to find credentials to authenticate itself to the apiserver. + - `--kubeconfig` tells kubelet where to find credentials to authenticate itself to the apiserver. - `--cloud_provider=` tells the kubelet how to talk to a cloud provider to read metadata about itself. - `--register-node` tells the kubelet to create its own node resource.