红帽全球峰会6.11. Freeing node resources using garbage collection
As an administrator, you can use OpenShift Container Platform to ensure that your nodes are running efficiently by freeing up resources through garbage collection.
The OpenShift Container Platform node performs two types of garbage collection:
- Container garbage collection: Removes terminated containers.
- Image garbage collection: Removes images not referenced by any running pods.
You can help ensure that your nodes are running efficiently by using container garbage collection to remove terminated containers.
When eviction thresholds are set for garbage collection, the node tries to keep any container for any pod accessible from the API. If the pod has been deleted, the containers will be as well. Containers are preserved as long the pod is not deleted and the eviction threshold is not reached. If the node is under disk pressure, it will remove containers and their logs will no longer be accessible using oc logs.
- eviction-soft - A soft eviction threshold pairs an eviction threshold with a required administrator-specified grace period.
- eviction-hard - A hard eviction threshold has no grace period, and if observed, OpenShift Container Platform takes immediate action.
The following table lists the eviction thresholds:
| Node condition | Eviction signal | Description |
|---|---|---|
| MemoryPressure |
| The available memory on the node. |
| DiskPressure |
|
The available disk space or inodes on the node root file system, |
For evictionHard you must specify all of these parameters. If you do not specify all parameters, only the specified parameters are applied and the garbage collection will not function properly.
If a node is oscillating above and below a soft eviction threshold, but not exceeding its associated grace period, the corresponding node would constantly oscillate between true and false. As a consequence, the scheduler could make poor scheduling decisions.
To protect against this oscillation, use the evictionpressure-transition-period flag to control how long OpenShift Container Platform must wait before transitioning out of a pressure condition. OpenShift Container Platform will not set an eviction threshold as being met for the specified pressure condition for the period specified before toggling the condition back to false.
Setting the evictionPressureTransitionPeriod parameter to 0 configures the default value of 5 minutes. You cannot set an eviction pressure transition period to zero seconds.
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