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Pruning objects to reclaim resources

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Over time, API objects created in Red Hat OpenShift Service on AWS can accumulate in the cluster’s etcd data store through normal user operations, such as when building and deploying applications.

A user with the dedicated-admin role can periodically prune older versions of objects from the cluster that are no longer required. For example, by pruning images you can delete older images and layers that are no longer in use, but are still taking up disk space.

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Basic pruning operations

The CLI groups prune operations under a common parent command:

$ oc adm prune <object_type> <options>

This specifies:

  • The <object_type> to perform the action on, such as groups, builds, deployments, or images.

  • The <options> supported to prune that object type.

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Pruning groups

To prune groups records from an external provider, administrators can run the following command:

$ oc adm prune groups \
    --sync-config=path/to/sync/config [<options>]
Table 1. oc adm prune groups flags
Options Description

--confirm

Indicate that pruning should occur, instead of performing a dry-run.

--blacklist

Path to the group blacklist file.

--whitelist

Path to the group whitelist file.

--sync-config

Path to the synchronization configuration file.
Procedure

  1. To see the groups that the prune command deletes, run the following command:

    $ oc adm prune groups --sync-config=ldap-sync-config.yaml

  2. To perform the prune operation, add the --confirm flag:

    $ oc adm prune groups --sync-config=ldap-sync-config.yaml --confirm
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Pruning deployment resources

You can prune resources associated with deployments that are no longer required by the system, due to age and status.

The following command prunes replication controllers associated with DeploymentConfig objects:

$ oc adm prune deployments [<options>]

To also prune replica sets associated with Deployment objects, use the --replica-sets flag. This flag is currently a Technology Preview feature.
Table 2. oc adm prune deployments flags
Option Description

--confirm

Indicate that pruning should occur, instead of performing a dry-run.

--keep-complete=<N>

Per the DeploymentConfig object, keep the last N replication controllers that have a status of Complete and replica count of zero. The default is 5.

--keep-failed=<N>

Per the DeploymentConfig object, keep the last N replication controllers that have a status of Failed and replica count of zero. The default is 1.

--keep-younger-than=<duration>

Do not prune any replication controller that is younger than <duration> relative to the current time. Valid units of measurement include nanoseconds (ns), microseconds (us), milliseconds (ms), seconds (s), minutes (m), and hours (h). The default is 60m.

--orphans

Prune all replication controllers that no longer have a DeploymentConfig object, has status of Complete or Failed, and has a replica count of zero.
Procedure

  1. To see what a pruning operation would delete, run the following command:

    $ oc adm prune deployments --orphans --keep-complete=5 --keep-failed=1 \
    --keep-younger-than=60m

  2. To actually perform the prune operation, add the --confirm flag:

    $ oc adm prune deployments --orphans --keep-complete=5 --keep-failed=1 \
    --keep-younger-than=60m --confirm
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Pruning builds

To prune builds that are no longer required by the system due to age and status, administrators can run the following command:

$ oc adm prune builds [<options>]
Table 3. oc adm prune builds flags
Option Description

--confirm

Indicate that pruning should occur, instead of performing a dry-run.

--orphans

Prune all builds whose build configuration no longer exists, status is complete, failed, error, or canceled.

--keep-complete=<N>

Per build configuration, keep the last N builds whose status is complete. The default is 5.

--keep-failed=<N>

Per build configuration, keep the last N builds whose status is failed, error, or canceled. The default is 1.

--keep-younger-than=<duration>

Do not prune any object that is younger than <duration> relative to the current time. The default is 60m.
Procedure

  1. To see what a pruning operation would delete, run the following command:

    $ oc adm prune builds --orphans --keep-complete=5 --keep-failed=1 \
    --keep-younger-than=60m

  2. To actually perform the prune operation, add the --confirm flag:

    $ oc adm prune builds --orphans --keep-complete=5 --keep-failed=1 \
    --keep-younger-than=60m --confirm

Developers can enable automatic build pruning by modifying their build configuration.
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Automatically pruning images

Images from the OpenShift image registry that are no longer required by the system due to age, status, or exceed limits are automatically pruned. Cluster administrators can configure the Pruning Custom Resource, or suspend it.

Prerequisites

  • You have access to an Red Hat OpenShift Service on AWS cluster using an account with dedicated-admin permissions.

  • Install the oc CLI.

Procedure

  • Verify that the object named imagepruners.imageregistry.operator.openshift.io/cluster contains the following spec and status fields:

spec:
  schedule: 0 0 * * * (1)
  suspend: false (2)
  keepTagRevisions: 3 (3)
  keepYoungerThanDuration: 60m (4)
  keepYoungerThan: 3600000000000 (5)
  resources: {} (6)
  affinity: {} (7)
  nodeSelector: {} (8)
  tolerations: [] (9)
  successfulJobsHistoryLimit: 3 (10)
  failedJobsHistoryLimit: 3 (11)
status:
  observedGeneration: 2 (12)
  conditions: (13)
  - type: Available
    status: "True"
    lastTransitionTime: 2019-10-09T03:13:45
    reason: Ready
    message: "Periodic image pruner has been created."
  - type: Scheduled
    status: "True"
    lastTransitionTime: 2019-10-09T03:13:45
    reason: Scheduled
    message: "Image pruner job has been scheduled."
  - type: Failed
    staus: "False"
    lastTransitionTime: 2019-10-09T03:13:45
    reason: Succeeded
    message: "Most recent image pruning job succeeded."
1 schedule: CronJob formatted schedule. This is an optional field, default is daily at midnight.
2 suspend: If set to true, the CronJob running pruning is suspended. This is an optional field, default is false. The initial value on new clusters is false.
3 keepTagRevisions: The number of revisions per tag to keep. This is an optional field, default is 3. The initial value is 3.
4 keepYoungerThanDuration: Retain images younger than this duration. This is an optional field. If a value is not specified, either keepYoungerThan or the default value 60m (60 minutes) is used.
5 keepYoungerThan: Deprecated. The same as keepYoungerThanDuration, but the duration is specified as an integer in nanoseconds. This is an optional field. When keepYoungerThanDuration is set, this field is ignored.
6 resources: Standard pod resource requests and limits. This is an optional field.
7 affinity: Standard pod affinity. This is an optional field.
8 nodeSelector: Standard pod node selector. This is an optional field.
9 tolerations: Standard pod tolerations. This is an optional field.
10 successfulJobsHistoryLimit: The maximum number of successful jobs to retain. Must be >= 1 to ensure metrics are reported. This is an optional field, default is 3. The initial value is 3.
11 failedJobsHistoryLimit: The maximum number of failed jobs to retain. Must be >= 1 to ensure metrics are reported. This is an optional field, default is 3. The initial value is 3.
12 observedGeneration: The generation observed by the Operator.
13 conditions: The standard condition objects with the following types:

  • Available: Indicates if the pruning job has been created. Reasons can be Ready or Error.

  • Scheduled: Indicates if the next pruning job has been scheduled. Reasons can be Scheduled, Suspended, or Error.

  • Failed: Indicates if the most recent pruning job failed.

The Image Registry Operator’s behavior for managing the pruner is orthogonal to the managementState specified on the Image Registry Operator’s ClusterOperator object. If the Image Registry Operator is not in the Managed state, the image pruner can still be configured and managed by the Pruning Custom Resource.

However, the managementState of the Image Registry Operator alters the behavior of the deployed image pruner job:

  • Managed: the --prune-registry flag for the image pruner is set to true.

  • Removed: the --prune-registry flag for the image pruner is set to false, meaning it only prunes image metadata in etcd.
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Pruning cron jobs

Cron jobs can perform pruning of successful jobs, but might not properly handle failed jobs. Therefore, the cluster administrator should perform regular cleanup of jobs manually. They should also restrict the access to cron jobs to a small group of trusted users and set appropriate quota to prevent the cron job from creating too many jobs and pods.

Additional resources