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Merge pull request #124 from MaciekPytel/ca_0_6_faq 

CA 0.6 FAQ update
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Marcin Wielgus 2017-06-19 10:43:43 +02:00 committed by GitHub
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# Frequently Asked Questions
# Older versions
The answers in this FAQ apply to the newest version of Cluster Autoscaler. If
you're using an older version of CA please refer to corresponding version of
this document:
[Cluster Autoscaler 0.5.X](https://github.com/kubernetes/autoscaler/blob/cluster-autoscaler-release-0.5/cluster-autoscaler/FAQ.md)
# Table of Contents:
<!--- TOC BEGIN -->
* [Basics](#basics)
@ -11,6 +18,9 @@
* [Should I use a CPU-usage-based node autoscaler with Kubernetes?](#should-i-use-a-cpuusagebased-node-autoscaler-with-kubernetes)
* [How is Cluster Autoscaler different from CPU-usage-based node autoscalers?](#how-is-cluster-autoscaler-different-from-cpuusagebased-node-autoscalers)
* [Is Cluster Autoscaler compatible with CPU-usage-based node autoscalers?](#is-cluster-autoscaler-compatible-with-cpuusagebased-node-autoscalers)
* [How to?](#how-to)
* [I'm running cluster with nodes in multiple zones for HA purposes. Is that supported by Cluster Autoscaler?](#im-running-cluster-with-nodes-in-multiple-zones-for-ha-purposes-is-that-supported-by-cluster-autoscaler)
* [How can I monitor Cluster Autoscaler?](#how-can-i-monitor-cluster-autoscaler)
* [Internals](#internals)
* [Are all of the mentioned heuristics and timings final?](#are-all-of-the-mentioned-heuristics-and-timings-final)
* [How does scale up work?](#how-does-scale-up-work)
@ -94,6 +104,39 @@ They are also not particularly suited to use with Kubernetes in general.
****************
# How to?
### I'm running cluster with nodes in multiple zones for HA purposes. Is that supported by Cluster Autoscaler?
CA 0.6 introduced `--balance-similar-node-groups` flag to support this use-case. If you set the flag to true
CA will automatically identify node groups using the same instance types and
having the same set of labels (except for automatically added zone labels) and try to
keep the size of those node groups balanced.
This does not guarantee similar node groups will have exactly the same sizes:
* Currently the balancing is only done at scale-up. Cluster Autoscaler will
still scale-down underutilized nodes regardless of relative size of underlying
node groups. We plan to take balancing into account in scale-down in the future.
* Cluster Autoscaler will only add as many nodes as required to run all existing
pods. If the number of nodes is not divisible by number of balanced node
groups some groups will get 1 more node than others.
* Cluster Autoscaler will only balance between node groups that can support the
same set of pending pods. If you run pods that can only go to a single node group
(for example due to nodeSelector on zone label) CA will only add nodes to
this particular node group.
You can opt-out a node group from being automatically balanced with other node
groups using the same instance type by giving it any custom label.
### How can I monitor Cluster Autoscaler?
Cluster Autoscaler provides metrics and livenessProbe endpoints. By
default they're available on port 8085 (configurable with `--address` flag),
respectively under /metrics and /health-check.
Metrics are provided in Prometheus format and their detailed description is
available [here](https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/proposals/metrics.md).
****************
# Internals
### Are all of the mentioned heuristics and timings final?