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The k8s project recently cut over to the new official k8s.gcr.io container registry. The descheduler image can now be pulled from k8s.gcr.io. This is just a new DNS name for the container registry. The previously documented DNS names for the registry still work, but require more typing.
98 lines
5.0 KiB
Markdown
98 lines
5.0 KiB
Markdown
# User Guide
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Starting with descheduler release v0.10.0 container images are available in the official k8s container registry.
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* `k8s.gcr.io/descheduler/descheduler`
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## Policy Configuration Examples
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The [examples](https://github.com/kubernetes-sigs/descheduler/tree/master/examples) directory has descheduler policy configuration examples.
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## CLI Options
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The descheduler has many CLI options that can be used to override its default behavior.
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```
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descheduler --help
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The descheduler evicts pods which may be bound to less desired nodes
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Usage:
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descheduler [flags]
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descheduler [command]
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Available Commands:
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help Help about any command
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version Version of descheduler
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Flags:
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--add-dir-header If true, adds the file directory to the header
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--alsologtostderr log to standard error as well as files
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--descheduling-interval duration Time interval between two consecutive descheduler executions. Setting this value instructs the descheduler to run in a continuous loop at the interval specified.
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--dry-run execute descheduler in dry run mode.
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--evict-local-storage-pods Enables evicting pods using local storage by descheduler
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-h, --help help for descheduler
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--kubeconfig string File with kube configuration.
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--log-backtrace-at traceLocation when logging hits line file:N, emit a stack trace (default :0)
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--log-dir string If non-empty, write log files in this directory
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--log-file string If non-empty, use this log file
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--log-file-max-size uint Defines the maximum size a log file can grow to. Unit is megabytes. If the value is 0, the maximum file size is unlimited. (default 1800)
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--log-flush-frequency duration Maximum number of seconds between log flushes (default 5s)
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--logtostderr log to standard error instead of files (default true)
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--max-pods-to-evict-per-node int Limits the maximum number of pods to be evicted per node by descheduler
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--node-selector string Selector (label query) to filter on, supports '=', '==', and '!='.(e.g. -l key1=value1,key2=value2)
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--policy-config-file string File with descheduler policy configuration.
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--skip-headers If true, avoid header prefixes in the log messages
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--skip-log-headers If true, avoid headers when opening log files
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--stderrthreshold severity logs at or above this threshold go to stderr (default 2)
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-v, --v Level number for the log level verbosity
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--vmodule moduleSpec comma-separated list of pattern=N settings for file-filtered logging
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Use "descheduler [command] --help" for more information about a command.
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```
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## Production Use Cases
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This section contains descriptions of real world production use cases.
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### Balance Cluster By Pod Age
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When initially migrating applications from a static virtual machine infrastructure to a cloud native k8s
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infrastructure there can be a tendency to treat application pods like static virtual machines. One approach
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to help prevent developers and operators from treating pods like virtual machines is to ensure that pods
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only run for a fixed amount
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of time.
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The `PodLifeTime` strategy can be used to ensure that old pods are evicted. It is recommended to create a
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[pod disruption budget](https://kubernetes.io/docs/tasks/run-application/configure-pdb/) for each
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application to ensure application availability.
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```
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descheduler -v=3 --evict-local-storage-pods --policy-config-file=pod-life-time.yml
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```
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This policy configuration file ensures that pods created more than 7 days ago are evicted.
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```
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---
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apiVersion: "descheduler/v1alpha1"
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kind: "DeschedulerPolicy"
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strategies:
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"LowNodeUtilization":
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enabled: false
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"RemoveDuplicates":
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enabled: false
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"RemovePodsViolatingInterPodAntiAffinity":
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enabled: false
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"RemovePodsViolatingNodeAffinity":
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enabled: false
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"RemovePodsViolatingNodeTaints":
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enabled: false
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"RemovePodsHavingTooManyRestarts":
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enabled: false
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"PodLifeTime":
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enabled: true
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params:
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maxPodLifeTimeSeconds: 604800 # pods run for a maximum of 7 days
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```
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### Autoheal Node Problems
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Descheduler's `RemovePodsViolatingNodeTaints` strategy can be combined with
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[Node Problem Detector](https://github.com/kubernetes/node-problem-detector/) and
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[Cluster Autoscaler](https://github.com/kubernetes/autoscaler/tree/master/cluster-autoscaler) to automatically remove
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Nodes which have problems. Node Problem Detector can detect specific Node problems and taint any Nodes which have those
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problems. The Descheduler will then deschedule workloads from those Nodes. Finally, if the descheduled Node's resource
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allocation falls below the Cluster Autoscaler's scale down threshold, the Node will become a scale down candidate
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and can be removed by Cluster Autoscaler. These three components form an autohealing cycle for Node problems.
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