mirror of
https://github.com/optim-enterprises-bv/kubernetes.git
synced 2025-11-04 04:08:16 +00:00
102 lines
5.4 KiB
Markdown
102 lines
5.4 KiB
Markdown
<!-- BEGIN MUNGE: UNVERSIONED_WARNING -->
|
|
|
|
<!-- BEGIN STRIP_FOR_RELEASE -->
|
|
|
|
<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
|
|
width="25" height="25">
|
|
<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
|
|
width="25" height="25">
|
|
<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
|
|
width="25" height="25">
|
|
<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
|
|
width="25" height="25">
|
|
<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
|
|
width="25" height="25">
|
|
|
|
<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
|
|
|
|
If you are using a released version of Kubernetes, you should
|
|
refer to the docs that go with that version.
|
|
|
|
<!-- TAG RELEASE_LINK, added by the munger automatically -->
|
|
<strong>
|
|
The latest release of this document can be found
|
|
[here](http://releases.k8s.io/release-1.1/docs/admin/multi-cluster.md).
|
|
|
|
Documentation for other releases can be found at
|
|
[releases.k8s.io](http://releases.k8s.io).
|
|
</strong>
|
|
--
|
|
|
|
<!-- END STRIP_FOR_RELEASE -->
|
|
|
|
<!-- END MUNGE: UNVERSIONED_WARNING -->
|
|
|
|
# Considerations for running multiple Kubernetes clusters
|
|
|
|
You may want to set up multiple Kubernetes clusters, both to
|
|
have clusters in different regions to be nearer to your users, and to tolerate failures and/or invasive maintenance.
|
|
This document describes some of the issues to consider when making a decision about doing so.
|
|
|
|
Note that at present,
|
|
Kubernetes does not offer a mechanism to aggregate multiple clusters into a single virtual cluster. However,
|
|
we [plan to do this in the future](../proposals/federation.md).
|
|
|
|
## Scope of a single cluster
|
|
|
|
On IaaS providers such as Google Compute Engine or Amazon Web Services, a VM exists in a
|
|
[zone](https://cloud.google.com/compute/docs/zones) or [availability
|
|
zone](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html).
|
|
We suggest that all the VMs in a Kubernetes cluster should be in the same availability zone, because:
|
|
- compared to having a single global Kubernetes cluster, there are fewer single-points of failure
|
|
- compared to a cluster that spans availability zones, it is easier to reason about the availability properties of a
|
|
single-zone cluster.
|
|
- when the Kubernetes developers are designing the system (e.g. making assumptions about latency, bandwidth, or
|
|
correlated failures) they are assuming all the machines are in a single data center, or otherwise closely connected.
|
|
|
|
It is okay to have multiple clusters per availability zone, though on balance we think fewer is better.
|
|
Reasons to prefer fewer clusters are:
|
|
- improved bin packing of Pods in some cases with more nodes in one cluster (less resource fragmentation)
|
|
- reduced operational overhead (though the advantage is diminished as ops tooling and processes matures)
|
|
- reduced costs for per-cluster fixed resource costs, e.g. apiserver VMs (but small as a percentage
|
|
of overall cluster cost for medium to large clusters).
|
|
|
|
Reasons to have multiple clusters include:
|
|
- strict security policies requiring isolation of one class of work from another (but, see Partitioning Clusters
|
|
below).
|
|
- test clusters to canary new Kubernetes releases or other cluster software.
|
|
|
|
## Selecting the right number of clusters
|
|
|
|
The selection of the number of Kubernetes clusters may be a relatively static choice, only revisited occasionally.
|
|
By contrast, the number of nodes in a cluster and the number of pods in a service may be change frequently according to
|
|
load and growth.
|
|
|
|
To pick the number of clusters, first, decide which regions you need to be in to have adequate latency to all your end users, for services that will run
|
|
on Kubernetes (if you use a Content Distribution Network, the latency requirements for the CDN-hosted content need not
|
|
be considered). Legal issues might influence this as well. For example, a company with a global customer base might decide to have clusters in US, EU, AP, and SA regions.
|
|
Call the number of regions to be in `R`.
|
|
|
|
Second, decide how many clusters should be able to be unavailable at the same time, while still being available. Call
|
|
the number that can be unavailable `U`. If you are not sure, then 1 is a fine choice.
|
|
|
|
If it is allowable for load-balancing to direct traffic to any region in the event of a cluster failure, then
|
|
you need at least the larger of `R` or `U + 1` clusters. If it is not (e.g you want to ensure low latency for all
|
|
users in the event of a cluster failure), then you need to have `R * (U + 1)` clusters
|
|
(`U + 1` in each of `R` regions). In any case, try to put each cluster in a different zone.
|
|
|
|
Finally, if any of your clusters would need more than the maximum recommended number of nodes for a Kubernetes cluster, then
|
|
you may need even more clusters. Kubernetes v1.0 currently supports clusters up to 100 nodes in size, but we are targeting
|
|
1000-node clusters by early 2016.
|
|
|
|
## Working with multiple clusters
|
|
|
|
When you have multiple clusters, you would typically create services with the same config in each cluster and put each of those
|
|
service instances behind a load balancer (AWS Elastic Load Balancer, GCE Forwarding Rule or HTTP Load Balancer) spanning all of them, so that
|
|
failures of a single cluster are not visible to end users.
|
|
|
|
|
|
<!-- BEGIN MUNGE: GENERATED_ANALYTICS -->
|
|
[]()
|
|
<!-- END MUNGE: GENERATED_ANALYTICS -->
|