Documentation for dynamic volume limits based on node type (#8871)

* add cos for storage limits * Update docs specific for aws and gce * fix some minor things * Update storage-limits.md * Add k8s version to feature-state shortcode
2018-06-19 16:59:31 -04:00
parent fa92e2fc96
commit 53ec6a99e8
1 changed files with 73 additions and 0 deletions
@@ -0,0 +1,73 @@
+---
+reviewers:
+- jsafrane
+- saad-ali
+- thockin
+- msau42
+title: Node-specific Volume Limits
+content_template: templates/concept
+---
+
+{{% capture overview %}}
+
+This page describes the maximum number of volumes that can be attached
+to a node for various cloud providers.
+
+Cloud providers like Google, Amazon, and Microsoft typically have a limit on
+how many volumes can be attached to a node. It is important for Kubernetes to
+respect those limits. Otherwise, Pods scheduled on a node could get stuck
+waiting for volumes to attach.
+
+{{% /capture %}}
+
+{{% capture body %}}
+
+## Kubernetes default limits
+
+The Kubernetes scheduler has default limits on the number of volumes
+that can be attached to a node:
+
+<table>
+  <tr><th>Cloud service</th><th>Maximum volumes per node</th></tr>
+  <tr><td><a href="https://aws.amazon.com/ebs/">Amazon Elastic Block Store (EBS)</a></td><td>39</td></tr>
+  <tr><td><a href="https://cloud.google.com/persistent-disk/">Google Persistent Disk</a></td><td>16</td></tr>
+  <tr><td><a href="https://azure.microsoft.com/en-us/services/storage/main-disks/">Microsoft Azure Disk Storage</a></td><td>16</td></tr>
+</table>
+
+## Custom limits
+
+You can change these limits by setting the value of the
+`KUBE_MAX_PD_VOLS` environment variable, and then starting the scheduler.
+
+Use caution if you set a limit that is higher than the default limit. Consult
+the cloud provider's documentation to make sure that nodes can actually support
+the limit you set.
+
+The limit applies to the entire cluster, so it affects all nodes.
+
+## Dynamic volume limits
+
+{{< feature-state state="alpha" for_k8s_version="v1.11" >}}
+
+Kubernetes 1.11 introduces dynamic volume limits based on node type. This
+is an alpha feature that supports these services:
+
+- Amazon EBS
+- Google Persistent Disk
+
+To enable dynamic volume limits, use the `AttachVolumeLimit` flag.
+
+When the dynamic volume limits feature is enabled, Kubernetes automatically
+determines the node type and supports the appropriate number of attachable
+volumes for the node. For example:
+
+* On
+<a href="https://cloud.google.com/compute/">Google Compute Engine</a>,
+up to 128 volumes could be attached to a node, depending on the node type. 
+
+* For Amazon EBS disks on M5/C5 instance types, Kubernetes would permit only 25
+volumes to be attached to a node. For other instance types on
+<a href="https://aws.amazon.com/ec2/">Amazon Elastic Compute Cloud (EC2)</a>,
+Kubernetes would permit 39 volumes to be attached.
+
+{{% /capture %}}