Move Guide topic: kubelet Garbage Collection. (#3301)
This commit is contained in:
Steve Perry
@@ -55,6 +55,7 @@ toc:
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- docs/concepts/cluster-administration/audit.md
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- docs/concepts/cluster-administration/resource-usage-monitoring.md
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- docs/concepts/cluster-administration/out-of-resource.md
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- docs/concepts/cluster-administration/kubelet-garbage-collection.md
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- docs/concepts/cluster-administration/cluster-management.md
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- docs/concepts/cluster-administration/multiple-clusters.md
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- docs/concepts/cluster-administration/federation.md
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@@ -4,72 +4,7 @@ assignees:
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title: Configuring kubelet Garbage Collection
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---
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* TOC
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{:toc}
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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.
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{% include user-guide-content-moved.md %}
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External garbage collection tools are not recommended as these tools can potentially break the behavior of kubelet by removing containers expected to exist.
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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 takes two factors into consideration:
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`HighThresholdPercent` and `LowThresholdPercent`. Disk usage above the high threshold
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will trigger garbage collection. The garbage collection will delete least recently used images until the low
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threshold has been met.
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### Container Collection
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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
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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.
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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`.
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Containers that are not managed by kubelet are not subject to container garbage collection.
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### User Configuration
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Users can adjust the following thresholds to tune image garbage collection with the following kubelet flags :
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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 through the following kubelet 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 0 minute, which means every finished container will be garbaged collected.
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2. `maximum-dead-containers-per-container`, maximum number of old instances to be retained
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per container. Default is 1.
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3. `maximum-dead-containers`, maximum number of old instances of containers to retain globally.
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Default is -1, which means there is no global limit.
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Containers can potentially be garbage collected before their usefulness has expired. These containers
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can contain logs and other data that can be useful for troubleshooting. A sufficiently large value for
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`maximum-dead-containers-per-container` is highly recommended to allow at least 1 dead container to be
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retained per expected container. A larger value for `maximum-dead-containers` is also recommended for a
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similar reason.
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See [this issue](https://github.com/kubernetes/kubernetes/issues/13287) for more details.
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### Deprecation
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Some kubelet Garbage Collection features in this doc will be replaced by kubelet eviction in the future.
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Including:
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| Existing Flag | New Flag | Rationale |
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| ------------- | -------- | --------- |
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| `--image-gc-high-threshold` | `--eviction-hard` or `--eviction-soft` | existing eviction signals can trigger image garbage collection |
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| `--image-gc-low-threshold` | `--eviction-minimum-reclaim` | eviction reclaims achieve the same behavior |
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| `--maximum-dead-containers` | | deprecated once old logs are stored outside of container's context |
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| `--maximum-dead-containers-per-container` | | deprecated once old logs are stored outside of container's context |
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| `--minimum-container-ttl-duration` | | deprecated once old logs are stored outside of container's context |
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| `--low-diskspace-threshold-mb` | `--eviction-hard` or `eviction-soft` | eviction generalizes disk thresholds to other resources |
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| `--outofdisk-transition-frequency` | `--eviction-pressure-transition-period` | eviction generalizes disk pressure transition to other resources |
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See [Configuring Out Of Resource Handling](/docs/admin/out-of-resource/) for more details.
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[kubelet Garbage Collection](/docs/concepts/cluster-administration/kubelet-garbage-collection/)
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@@ -0,0 +1,75 @@
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---
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assignees:
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- mikedanese
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title: Configuring kubelet Garbage Collection
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---
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* TOC
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{:toc}
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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.
|
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External garbage collection tools are not recommended as these tools can potentially break the behavior of kubelet by removing containers expected to exist.
|
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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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|
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The policy for garbage collecting images takes two factors into consideration:
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`HighThresholdPercent` and `LowThresholdPercent`. Disk usage above the high threshold
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will trigger garbage collection. The garbage collection will delete least recently used images until the low
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threshold has been met.
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|
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### Container Collection
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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
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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.
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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`.
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Containers that are not managed by kubelet are not subject to container garbage collection.
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|
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### User Configuration
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|
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Users can adjust the following thresholds to tune image garbage collection with the following kubelet flags :
|
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|
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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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|
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We also allow users to customize garbage collection policy through the following kubelet flags:
|
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|
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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 0 minute, which means every finished container will be garbaged collected.
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2. `maximum-dead-containers-per-container`, maximum number of old instances to be retained
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per container. Default is 1.
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3. `maximum-dead-containers`, maximum number of old instances of containers to retain globally.
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Default is -1, which means there is no global limit.
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Containers can potentially be garbage collected before their usefulness has expired. These containers
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can contain logs and other data that can be useful for troubleshooting. A sufficiently large value for
|
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`maximum-dead-containers-per-container` is highly recommended to allow at least 1 dead container to be
|
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retained per expected container. A larger value for `maximum-dead-containers` is also recommended for a
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similar reason.
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See [this issue](https://github.com/kubernetes/kubernetes/issues/13287) for more details.
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### Deprecation
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Some kubelet Garbage Collection features in this doc will be replaced by kubelet eviction in the future.
|
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|
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Including:
|
||||
|
||||
| Existing Flag | New Flag | Rationale |
|
||||
| ------------- | -------- | --------- |
|
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| `--image-gc-high-threshold` | `--eviction-hard` or `--eviction-soft` | existing eviction signals can trigger image garbage collection |
|
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| `--image-gc-low-threshold` | `--eviction-minimum-reclaim` | eviction reclaims achieve the same behavior |
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| `--maximum-dead-containers` | | deprecated once old logs are stored outside of container's context |
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| `--maximum-dead-containers-per-container` | | deprecated once old logs are stored outside of container's context |
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| `--minimum-container-ttl-duration` | | deprecated once old logs are stored outside of container's context |
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| `--low-diskspace-threshold-mb` | `--eviction-hard` or `eviction-soft` | eviction generalizes disk thresholds to other resources |
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| `--outofdisk-transition-frequency` | `--eviction-pressure-transition-period` | eviction generalizes disk pressure transition to other resources |
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See [Configuring Out Of Resource Handling](/docs/admin/out-of-resource/) for more details.
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