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Fix grammatical issues in node.md

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Sam Ghods
2016-10-27 04:47:04 -07:00
committed by Devin Donnelly
parent 1a6df75cf5
commit eda196d356
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@@ -11,44 +11,39 @@ assignees:
## What is a node? ## What is a node?
`Node` is a worker machine in Kubernetes, previously known as `Minion`. Node A `node` is a worker machine in Kubernetes, previously known as a `minion`. A node
may be a VM or physical machine, depending on the cluster. Each node has may be a VM or physical machine, depending on the cluster. Each node has
the services necessary to run [Pods](/docs/user-guide/pods) and is managed by the master the services necessary to run [pods](/docs/user-guide/pods) and is managed by the master
components. The services on a node include docker, kubelet and network proxy. See components. The services on a node include Docker, kubelet and kube-proxy. See
[The Kubernetes Node](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/architecture.md#the-kubernetes-node) section in the [The Kubernetes Node](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/architecture.md#the-kubernetes-node) section in the
architecture design doc for more details. architecture design doc for more details.
## Node Status ## Node Status
Node status describes current status of a node. For now, there are the following A node's status is comprised of the following information.
pieces of information:
### Node Addresses ### Addresses
The usage of these fields varies depending on your cloud provider or bare metal configuration. The usage of these fields varies depending on your cloud provider or bare metal configuration.
* HostName: The hostname as reported by the node's kernel. Can be overridden via the kubelet `--hostname-override` parameter. * HostName: The hostname as reported by the node's kernel. Can be overridden via the kubelet `--hostname-override` parameter.
* ExternalIP: Typically the IP address of the node that is externally routable (available from outside the cluster).
* InternalIP: Typically the IP address of the node that is routable only within the cluster.
* ExternalIP: Generally the IP address of the node that is externally routable (available from outside the cluster) ### Phase
* InternalIP: Generally the IP address of the node that is routable only within the cluster Deprecated: node phase is no longer used.
### Condition
### Node Phase
Deprecated: Node Phase is no longer used
### Node Condition
The `conditions` field describes the status of all `Running` nodes. The `conditions` field describes the status of all `Running` nodes.
| Node Condition | Description | | Node Condition | Description |
|----------------|-------------| |----------------|-------------|
| `OutOfDisk` | `True` if insufficient free space on the node for adding new pods, otherwise `False` | | `OutOfDisk` | `True` if there is insufficient free space on the node for adding new pods, otherwise `False` |
| `Ready` | `True` if the node is healthy ready to accept pods, `False` if the node is not healthy and is not accepting pods, and `Unknown` if the Node Controller has not heard from the node in the last 40 seconds | | `Ready` | `True` if the node is healthy and ready to accept pods, `False` if the node is not healthy and is not accepting pods, and `Unknown` if the node controller has not heard from the node in the last 40 seconds |
Node condition is represented as a JSON object. For example, the following response describes a healthy node: The node condition is represented as a JSON object. For example, the following response describes a healthy node.
conditions mean the node is in sane state:
```json ```json
"conditions": [ "conditions": [
@@ -63,25 +58,26 @@ If the Status of the Ready condition is "Unknown" or "False" for longer than the
In versions of Kubernetes prior to 1.5, the node controller would [force delete](/docs/user-guide/pods/#force-deletion-of-pods) these unreachable pods from the apiserver. However, in 1.5 and higher, the node controller does not force delete pods until it is confirmed that they have stopped running in the cluster. One can see these pods which may be running on an unreachable node as being in the "Terminating" or "Unknown" states. In cases where Kubernetes cannot deduce from the underlying infrastructure if a node has permanently left a cluster, the cluster administrator may need to delete the node object by hand. Deleting the node object from Kubernetes causes all the Pod objects running on it to be deleted from the apiserver, freeing up their names. In versions of Kubernetes prior to 1.5, the node controller would [force delete](/docs/user-guide/pods/#force-deletion-of-pods) these unreachable pods from the apiserver. However, in 1.5 and higher, the node controller does not force delete pods until it is confirmed that they have stopped running in the cluster. One can see these pods which may be running on an unreachable node as being in the "Terminating" or "Unknown" states. In cases where Kubernetes cannot deduce from the underlying infrastructure if a node has permanently left a cluster, the cluster administrator may need to delete the node object by hand. Deleting the node object from Kubernetes causes all the Pod objects running on it to be deleted from the apiserver, freeing up their names.
### Node Capacity ### Capacity
Describes the resources available on the node: CPUs, memory and the maximum Describes the resources available on the node: CPU, memory and the maximum
number of pods that can be scheduled onto the node. number of pods that can be scheduled onto the node.
### Node Info ### Info
General information about the node, for instance kernel version, Kubernetes version General information about the node, such as kernel version, Kubernetes version
(kubelet version, kube-proxy version), docker version (if used), OS name. (kubelet and kube-proxy version), Docker version (if used), OS name.
The information is gathered by Kubelet from the node. The information is gathered by Kubelet from the node.
## Node Management ## Management
Unlike [Pods](/docs/user-guide/pods) and [Services](/docs/user-guide/services), a Node is not inherently Unlike [pods](/docs/user-guide/pods) and [services](/docs/user-guide/services),
created by Kubernetes: it is either taken from cloud providers like Google Compute Engine, a node is not inherently created by Kubernetes: it is created externally by cloud
or from your pool of physical or virtual machines. What this means is that when providers like Google Compute Engine, or exists in your pool of physical or virtual
Kubernetes creates a node, it is really just creating an object that represents the node in its internal state. machines. What this means is that when Kubernetes creates a node, it is really
After creation, Kubernetes will check whether the node is valid or not. just creating an object that represents the node. After creation, Kubernetes
For example, if you try to create a node from the following content: will check whether the node is valid or not. For example, if you try to create
a node from the following content:
```json ```json
{ {
@@ -96,117 +92,127 @@ 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 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 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 ignored for any cluster activity until it becomes valid. Note that Kubernetes
will keep the object for the invalid node unless it is explicitly deleted by the client, and it will keep will keep the object for the invalid node unless it is explicitly deleted by
checking to see if it becomes valid. the client, and it will keep checking to see if it becomes valid.
Currently, there are three components that interact with the Kubernetes node interface: Node Controller, Kubelet, and kubectl. Currently, there are three components that interact with the Kubernetes node
interface: node controller, kubelet, and kubectl.
### Node Controller ### Node Controller
Node controller is a component in Kubernetes master which manages Node The node controller is a Kubernetes master component which manages various
objects. aspects of nodes.
Node controller has mutliple roles in Node's life. First is assigning a CIDR block to The node controller has multiple roles in a node's life. The first is assigning a
the Node when it is registered (if CIDR assignment is turned on). Second is keeping the CIDR block to the node when it is registered (if CIDR assignment is turned on).
node controller's list of nodes up to date with the cloud provider's list of available
machines. When running in cloud environment whenever a node is unhealthy node controller The second is keeping the node controller's internal list of nodes up to date with
asks cloud provider if the VM for that node is still available. If not, the node the cloud provider's list of available machines. When running in a cloud
environment, whenever a node is unhealthy the node controller asks the cloud
provider if the VM for that node is still available. If not, the node
controller deletes the node from its list of nodes. controller deletes the node from its list of nodes.
Third responsibiliy is monitoring Node's health. Node controller is responsible for updating The third is monitoring the nodes' health. The node controller is
the NodeReady condition of NodeStatus to ConditionUnknown when a node becomes unreachable responsible for updating the NodeReady condition of NodeStatus to
(i.e. node controller stops receiving heartbeats e.g. due to the node being down), and then ConditionUnknown when a node becomes unreachable (i.e. the node controller stops
later evicting all the pods from the node (using graceful termination) if the node continues receiving heartbeats for some reason, e.g. due to the node being down), and then later evicting
to be unreachable (the current timeouts are 40s to start reporting ConditionUnknown and 5m all the pods from the node (using graceful termination) if the node continues
after that to start evicting pods). Node controller checks the state of each node every to be unreachable. (The default timeouts are 40s to start reporting
`--node-monitor-period` seconds. ConditionUnknown and 5m after that to start evicting pods.) The node controller
checks the state of each node every `--node-monitor-period` seconds.
In 1.4 release we updated the logic of node controller to better handle cases when a In Kubernetes 1.4, we updated the logic of the node controller to better handle
big number of Nodes have problems with reaching the master machine (e.g. because cases when a big number of nodes have problems with reaching the master
master machine has networking problem). Starting with 1.4 node controller will look at the (e.g. because the master has networking problem). Starting with 1.4, the node
state of all Nodes in the cluster when making a decision about pod eviction. controller will look at the state of all nodes in the cluster when making a
decision about pod eviction.
In most cases, node controller limits the eviction rate to `--node-eviction-rate` (default 0.1) In most cases, node controller limits the eviction rate to
per second, meaning it won't evict pods from more than 1 node per 10 seconds. `--node-eviction-rate` (default 0.1) per second, meaning it won't evict pods
from more than 1 node per 10 seconds.
The node eviction behavior changes when a node in a given availability zone becomes unhealthy, The node eviction behavior changes when a node in a given availability zone
node controller checks what percentage of nodes in the zone are unhealthy (NodeReady condition becomes unhealthy. The node controller checks what percentage of nodes in the zone
is ConditionUnknown or ConditionFalse) at the same time. If the fraction of unhealthy nodes is are unhealthy (NodeReady condition is ConditionUnknown or ConditionFalse) at
at least `--unhealthy-zone-threshold` (default 0.55) then the eviction rate is reduced: if the same time. If the fraction of unhealthy nodes is at least
the cluster is small (i.e. has less than or equal to `--large-cluster-size-threshold` `--unhealthy-zone-threshold` (default 0.55) then the eviction rate is reduced:
nodes - default 50) then evictions are stopped, otherwise the eviction rate is reduced to if the cluster is small (i.e. has less than or equal to
`--secondary-node-eviction-rate` (default 0.01) per second. The reason these policies are `--large-cluster-size-threshold` nodes - default 50) then evictions are
implemented per availability zone is because one availability zone might become partitioned stopped, otherwise the eviction rate is reduced to
from the master while the others remain connected. If your cluster does not span multiple cloud `--secondary-node-eviction-rate` (default 0.01) per second. The reason these
provider availability zones, then there is only one availability zone, namely the whole cluster. policies are implemented per availability zone is because one availability zone
might become partitioned from the master while the others remain connected. If
your cluster does not span multiple cloud provider availability zones, then
there is only one availability zone (the whole cluster).
A key reason for spreading your nodes across availability zones is so that workload can be A key reason for spreading your nodes across availability zones is so that the
shifted to healthy zones when one entire zone goes down. To enable this behavior, if all workload can be shifted to healthy zones when one entire zone goes down.
nodes in a zone are unhealthy then node controller evicts at the normal rate `--node-eviction-rate`. Therefore, if all nodes in a zone are unhealthy then node controller evicts at
The corner case for that is when all zones are completely unhealthy (i.e. there's no healthy node in the normal rate `--node-eviction-rate`. The corner case is when all zones are
the cluster). In such case node controller assumes that there's some problem with master machine completely unhealthy (i.e. there are no healthy nodes in the cluster). In such
connectivity and stops all evictions until any connectivity is restored. case, the node controller assumes that there's some problem with master
connectivity and stops all evictions until some connectivity is restored.
### Self-Registration of Nodes ### Self-Registration of Nodes
When kubelet flag `--register-node` is true (the default), the kubelet will attempt to When the kubelet flag `--register-node` is true (the default), the kubelet will attempt to
register itself with the API server. This is the preferred pattern, used by most distros. register itself with the API server. This is the preferred pattern, used by most distros.
For self-registration, the kubelet is started with the following options: For self-registration, the kubelet is started with the following options:
- `--api-servers=` tells the kubelet the location of the apiserver. - `--api-servers=` - Location of the apiservers.
- `--kubeconfig` tells kubelet where to find credentials to authenticate itself to the apiserver. - `--kubeconfig=` - Path to credentials to authenticate itself to the apiserver.
- `--cloud-provider=` tells the kubelet how to talk to a cloud provider to read metadata about itself. - `--cloud-provider=` - How to talk to a cloud provider to read metadata about itself.
- `--register-node` tells the kubelet to create its own node resource. - `--register-node` - Automatically register with the API server.
Currently, any kubelet is authorized to create/modify any node resource, but in practice it only creates/modifies Currently, any kubelet is authorized to create/modify any node resource, but in practice it only creates/modifies
its own. (In the future, we plan to limit authorization to only allow a kubelet to modify its own Node resource.) its own. (In the future, we plan to only allow a kubelet to modify its own node resource.)
#### Manual Node Administration #### Manual Node Administration
A cluster administrator can create and modify Node objects. A cluster administrator can create and modify node objects.
If the administrator wishes to create node objects manually, set kubelet flag If the administrator wishes to create node objects manually, set the kubelet flag
`--register-node=false`. `--register-node=false`.
The administrator can modify Node resources (regardless of the setting of `--register-node`). The administrator can modify node resources (regardless of the setting of `--register-node`).
Modifications include setting labels on the Node, and marking it unschedulable. Modifications include setting labels on the node and marking it unschedulable.
Labels on nodes can be used in conjunction with node selectors on pods to control scheduling, Labels on nodes can be used in conjunction with node selectors on pods to control scheduling,
e.g. to constrain a Pod to only be eligible to run on a subset of the nodes. e.g. to constrain a pod to only be eligible to run on a subset of the nodes.
Making a node unscheduleable will prevent new pods from being scheduled to that Marking a node as unscheduleable will prevent new pods from being scheduled to that
node, but will not affect any existing pods on the node. This is useful as a node, but will not affect any existing pods on the node. This is useful as a
preparatory step before a node reboot, etc. For example, to mark a node preparatory step before a node reboot, etc. For example, to mark a node
unschedulable, run this command: unschedulable, run this command:
```shell ```shell
kubectl patch nodes $NODENAME -p '{"spec": {"unschedulable": true}}' kubectl cordon $NODENAME
``` ```
Note that pods which are created by a daemonSet controller bypass the Kubernetes scheduler, Note that pods which are created by a daemonSet controller bypass the Kubernetes scheduler,
and do not respect the unschedulable attribute on a node. The assumption is that daemons belong on and do not respect the unschedulable attribute on a node. The assumption is that daemons belong on
the machine even if it is being drained of applications in preparation for a reboot. the machine even if it is being drained of applications in preparation for a reboot.
### Node capacity ### Node capacity
The capacity of the node (number of cpus and amount of memory) is part of the node resource. The capacity of the node (number of cpus and amount of memory) is part of the node object.
Normally, nodes register themselves and report their capacity when creating the node resource. If Normally, nodes register themselves and report their capacity when creating the node object. If
you are doing [manual node administration](#manual-node-administration), then you need to set node you are doing [manual node administration](#manual-node-administration), then you need to set node
capacity when adding a node. capacity when adding a node.
The Kubernetes scheduler ensures that there are enough resources for all the pods on a node. It The Kubernetes scheduler ensures that there are enough resources for all the pods on a node. It
checks that the sum of the limits of containers on the node is no greater than the node capacity. It checks that the sum of the limits of containers on the node is no greater than the node capacity. It
includes all containers started by kubelet, but not containers started directly by docker, nor includes all containers started by the kubelet, but not containers started directly by Docker nor
processes not in containers. processes not in containers.
If you want to explicitly reserve resources for non-Pod processes, you can create a placeholder If you want to explicitly reserve resources for non-pod processes, you can create a placeholder
pod. Use the following template: pod. Use the following template:
```yaml ```yaml
apiVersion: v1 apiVersion: v1