Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Documentation for NodeLease feature being promoted to GA #17189

Merged
merged 1 commit into from
Nov 18, 2019
Merged

Documentation for NodeLease feature being promoted to GA #17189

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
34 changes: 22 additions & 12 deletions content/en/docs/concepts/architecture/nodes.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -173,18 +173,28 @@ to be unreachable. (The default timeouts are 40s to start reporting
ConditionUnknown and 5m after that to start evicting pods.) The node controller
checks the state of each node every `--node-monitor-period` seconds.

In versions of Kubernetes prior to 1.13, NodeStatus is the heartbeat from the
node. Node lease feature is enabled by default since 1.14 as a beta feature
(feature gate `NodeLease`, [KEP-0009](https://github.com/kubernetes/enhancements/blob/master/keps/sig-node/0009-node-heartbeat.md)).
When node lease feature is enabled, each node has an associated `Lease` object in
`kube-node-lease` namespace that is renewed by the node periodically, and both
NodeStatus and node lease are treated as heartbeats from the node. Node leases
are renewed frequently while NodeStatus is reported from node to master only
when there is some change or enough time has passed (default is 1 minute, which
is longer than the default timeout of 40 seconds for unreachable nodes). Since
node lease is much more lightweight than NodeStatus, this feature makes node
heartbeat significantly cheaper from both scalability and performance
perspectives.
#### Heartbeats

wojtek-t marked this conversation as resolved.
Show resolved Hide resolved
Heartbeats, sent by Kubernetes nodes, help determine the availability of a node.
There are two forms of heartbeats: updates of `NodeStatus` and the
[Lease object](/docs/reference/generated/kubernetes-api/{{< latest-version >}}/#lease-v1-coordination-k8s-io).
Each Node has an associated Lease object in the `kube-node-lease`
{{< glossary_tooltip term_id="namespace" text="namespace">}}.
Lease is a lightweight resource, which improves the performance
of the node heartbeats as the cluster scales.

The kubelet is responsible for creating and updating the `NodeStatus` and
a Lease object.

- The kubelet updates the `NodeStatus` either when there is change in status,
or if there has been no update for a configured interval. The default interval
for `NodeStatus` updates is 5 minutes (much longer than the 40 second default
timeout for unreachable nodes).
- The kubelet creates and then updates its Lease object every 10 seconds
(the default update interval). Lease updates occur independently from the
`NodeStatus` updates.

#### Reliability

In Kubernetes 1.4, we updated the logic of the node controller to better handle
cases when a large number of nodes have problems with reaching the master
Expand Down
5 changes: 3 additions & 2 deletions content/en/docs/reference/command-line-tools-reference/feature-gates.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -100,8 +100,6 @@ different Kubernetes components.
| `LocalStorageCapacityIsolationFSQuotaMonitoring` | `false` | Alpha | 1.15 | |
| `MountContainers` | `false` | Alpha | 1.9 | |
| `NodeDisruptionExclusion` | `false` | Alpha | 1.16 | |
| `NodeLease` | `false` | Alpha | 1.12 | 1.13 |
| `NodeLease` | `true` | Beta | 1.14 | |
| `NonPreemptingPriority` | `false` | Alpha | 1.15 | |
| `PodOverhead` | `false` | Alpha | 1.16 | - |
| `PodShareProcessNamespace` | `false` | Alpha | 1.10 | 1.11 |
Expand Down Expand Up @@ -213,6 +211,9 @@ different Kubernetes components.
| `MountPropagation` | `false` | Alpha | 1.8 | 1.9 |
| `MountPropagation` | `true` | Beta | 1.10 | 1.11 |
| `MountPropagation` | `true` | GA | 1.12 | - |
| `NodeLease` | `false` | Alpha | 1.12 | 1.13 |
| `NodeLease` | `true` | Beta | 1.14 | 1.16 |
| `NodeLease` | `true` | GA | 1.17 | - |
| `PersistentLocalVolumes` | `false` | Alpha | 1.7 | 1.9 |
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

hello @wojtek-t . Some initial suggestions:

  • Line 205: Is the state GA?
  • Line 177: the kubelet or the Kubelet?
  • Line 182: This sentence could be reworded and possibly add more explanation, spelling too. Does this make sense?
    Compared to the Node resource, the Lease object is lightweight. The Lease resource improves the performance of the node heartbeats as the cluster scales?

From the KEP:
We will use that object to represent node heartbeat - for each Node there will be a corresponding Lease object with Name equal to Node name in a newly created dedicated namespace

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

rephrased

| `PersistentLocalVolumes` | `true` | Beta | 1.10 | 1.13 |
| `PersistentLocalVolumes` | `true` | GA | 1.14 | - |
Expand Down