Qiming Teng
ad93c9a6ef
This PR fixes the links in the concepts section. Most of the links are not dead links in English version because there are redirects for them. However, these links will be broken when localized to any languages other English. Where appropriate. this PR also wraps some long lines which are unfriendly to any localization team that try to catch the differences between revisions.
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title, content_type, weight
| title | content_type | weight |
|---|---|---|
| Garbage collection for container images | concept | 70 |
Garbage collection is a helpful function of kubelet that will clean up unused images and unused containers. Kubelet will perform garbage collection for containers every minute and garbage collection for images every five minutes.
External garbage collection tools are not recommended as these tools can potentially break the behavior of kubelet by removing containers expected to exist.
Image Collection
Kubernetes manages lifecycle of all images through imageManager, with the cooperation of cadvisor.
The policy for garbage collecting images takes two factors into consideration:
HighThresholdPercent and LowThresholdPercent. Disk usage above the high threshold
will trigger garbage collection. The garbage collection will delete least recently used images until the low
threshold has been met.
Container Collection
The policy for garbage collecting containers considers three user-defined variables.
MinAge is the minimum age at which a container can be garbage collected.
MaxPerPodContainer is the maximum number of dead containers every single
pod (UID, container name) pair is allowed to have.
MaxContainers is the maximum number of total dead containers.
These variables can be individually disabled by setting MinAge to zero and
setting MaxPerPodContainer and MaxContainers respectively to less than zero.
Kubelet will act on containers that are unidentified, deleted, or outside of
the boundaries set by the previously mentioned flags. The oldest containers
will generally be removed first. MaxPerPodContainer and MaxContainer may
potentially conflict with each other in situations where retaining the maximum
number of containers per pod (MaxPerPodContainer) would go outside the
allowable range of global dead containers (MaxContainers).
MaxPerPodContainer would be adjusted in this situation: A worst case
scenario would be to downgrade MaxPerPodContainer to 1 and evict the oldest
containers. Additionally, containers owned by pods that have been deleted are
removed once they are older than MinAge.
Containers that are not managed by kubelet are not subject to container garbage collection.
User Configuration
You can adjust the following thresholds to tune image garbage collection with the following kubelet flags :
image-gc-high-threshold, the percent of disk usage which triggers image garbage collection. Default is 85%.image-gc-low-threshold, the percent of disk usage to which image garbage collection attempts to free. Default is 80%.
You can customize the garbage collection policy through the following kubelet flags:
minimum-container-ttl-duration, minimum age for a finished container before it is garbage collected. Default is 0 minute, which means every finished container will be garbage collected.maximum-dead-containers-per-container, maximum number of old instances to be retained per container. Default is 1.maximum-dead-containers, maximum number of old instances of containers to retain globally. Default is -1, which means there is no global limit.
Containers can potentially be garbage collected before their usefulness has expired. These containers
can contain logs and other data that can be useful for troubleshooting. A sufficiently large value for
maximum-dead-containers-per-container is highly recommended to allow at least 1 dead container to be
retained per expected container. A larger value for maximum-dead-containers is also recommended for a
similar reason.
See this issue for more details.
Deprecation
Some kubelet Garbage Collection features in this doc will be replaced by kubelet eviction in the future.
Including:
| Existing Flag | New Flag | Rationale |
|---|---|---|
--image-gc-high-threshold |
--eviction-hard or --eviction-soft |
existing eviction signals can trigger image garbage collection |
--image-gc-low-threshold |
--eviction-minimum-reclaim |
eviction reclaims achieve the same behavior |
--maximum-dead-containers |
deprecated once old logs are stored outside of container's context | |
--maximum-dead-containers-per-container |
deprecated once old logs are stored outside of container's context | |
--minimum-container-ttl-duration |
deprecated once old logs are stored outside of container's context | |
--low-diskspace-threshold-mb |
--eviction-hard or eviction-soft |
eviction generalizes disk thresholds to other resources |
--outofdisk-transition-frequency |
--eviction-pressure-transition-period |
eviction generalizes disk pressure transition to other resources |
{{% heading "whatsnext" %}}
See Configuring Out Of Resource Handling for more details.