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110 lines
4.7 KiB
Markdown
110 lines
4.7 KiB
Markdown
<!-- BEGIN MUNGE: UNVERSIONED_WARNING -->
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<!-- BEGIN STRIP_FOR_RELEASE -->
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
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If you are using a released version of Kubernetes, you should
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refer to the docs that go with that version.
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<strong>
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The latest 1.0.x release of this document can be found
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[here](http://releases.k8s.io/release-1.0/docs/admin/garbage-collection.md).
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Documentation for other releases can be found at
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[releases.k8s.io](http://releases.k8s.io).
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</strong>
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--
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<!-- END STRIP_FOR_RELEASE -->
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<!-- END MUNGE: UNVERSIONED_WARNING -->
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# Garbage Collection
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- [Introduction](#introduction)
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- [Image Collection](#image-collection)
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- [Container Collection](#container-collection)
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- [User Configuration](#user-configuration)
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### Introduction
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Garbage collection is managed by kubelet automatically, mainly including unreferenced
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images and dead containers. kubelet applies container garbage collection every minute
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and image garbage collection every 5 minutes.
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Note that we don't recommend external garbage collection tool generally, since it could
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break the behavior of kubelet potentially if it attempts to remove all of the containers
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which acts as the tombstone kubelet relies on. Yet those garbage collector aims to deal
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with the docker leaking issues would be appreciated.
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### Image Collection
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kubernetes manages lifecycle of all images through imageManager, with the cooperation
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of cadvisor.
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The policy for garbage collecting images we apply takes two factors into consideration,
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`HighThresholdPercent` and `LowThresholdPercent`. Disk usage above the the high threshold
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will trigger garbage collection, which attempts to delete unused images until the low
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threshold is met. Least recently used images are deleted first.
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### Container Collection
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The policy for garbage collecting containers we apply takes on three variables, which can
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be user-defined. `MinAge` is the minimum age at which a container can be garbage collected,
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zero for no limit. `MaxPerPodContainer` is the max number of dead containers any single
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pod (UID, container name) pair is allowed to have, less than zero for no limit.
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`MaxContainers` is the max number of total dead containers, less than zero for no limit as well.
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kubelet sorts out containers which are unidentified or stay out of bounds set by previous
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mentioned three flags. Gernerally the oldest containers are removed first. Since we take both
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`MaxPerPodContainer` and `MaxContainers` into consideration, it could happen when they
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have conflict -- retaining the max number of containers per pod goes out of range set by max
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number of global dead containers. In this case, we would sacrifice the `MaxPerPodContainer`
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a little bit. For the worst case, we first downgrade it to 1 container per pod, and then
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evict the oldest containers for the greater good.
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When kubelet removes the dead containers, all the files inside the container will be cleaned up as well.
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Note that we will skip the containers that are not managed by kubelet.
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### User Configuration
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Users are free to set their own value to address image garbage collection.
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1. `image-gc-high-threshold`, the percent of disk usage which triggers image garbage collection.
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Default is 90%.
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2. `image-gc-low-threshold`, the percent of disk usage to which image garbage collection attempts
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to free. Default is 80%.
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We also allow users to customize garbage collection policy, basically via following three flags.
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1. `minimum-container-ttl-duration`, minimum age for a finished container before it is
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garbage collected. Default is 1 minute.
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2. `maximum-dead-containers-per-container`, maximum number of old instances to retain
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per container. Default is 2.
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3. `maximum-dead-containers`, maximum number of old instances of containers to retain globally.
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Default is 100.
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Note that we highly recommend a large enough value for `maximum-dead-containers-per-container`
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to allow at least 2 dead containers retaining per expected container when you customize the flag
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configuration. A loose value for `maximum-dead-containers` also assumes importance for a similar reason.
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See [this issue](https://github.com/kubernetes/kubernetes/issues/13287) for more details.
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<!-- BEGIN MUNGE: GENERATED_ANALYTICS -->
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[]()
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<!-- END MUNGE: GENERATED_ANALYTICS -->
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