crm_shadow

crm_shadow is a utility within the crmsh (Cluster Resource Manager Shell) toolkit used to work with a “shadow” copy of the cluster configuration (the CIB, or Cluster Information Base) in a Pacemaker-managed cluster. Although its usage is not as widely documented as some other crmsh commands, its primary functions generally include:

• Backup: Creating a shadow copy of the current active configuration. This backup can serve as a point-in-time snapshot of the cluster’s settings, which is useful for change management or for recovering from misconfigurations.

• Comparison: Comparing the current active CIB against a previously saved shadow copy. This helps administrators identify what changes have been made over time and can aid in troubleshooting configuration-related issues.

• Restore: In some implementations, crm_shadow may provide functionality to restore the cluster configuration from a shadow copy. This can be valuable if a recent change leads to instability or if the active CIB becomes corrupted.

Typical Operations

• Save the Active CIB to a Shadow File: This operation creates a backup of the current configuration.

  crm_shadow --save /path/to/shadow-cib.xml

  (Note: The actual flag or syntax might differ depending on the version of crmsh.)

• Compare a Shadow CIB with the Active Configuration: To display differences between the saved configuration and the current active one:

  crm_shadow --diff /path/to/shadow-cib.xml

• Restore the CIB from a Shadow Copy: This operation would replace the active configuration with the saved one:

  crm_shadow --restore /path/to/shadow-cib.xml

Considerations

• Version Dependency: The availability and exact syntax of crm_shadow can vary depending on the crmsh version and distribution. It’s recommended to check the help output:

  crm_shadow --help

  for the specific options and usage supported in your environment.

• Caution When Restoring: Because the CIB controls the cluster configuration, restoring from a shadow copy should be done with care—ideally after verifying that the shadow file is correct and tested in a non-production environment.

Conclusion

While crm_shadow may not be as commonly used or documented as other crmsh commands like crm_mon or crm_resource, it plays a valuable role in cluster configuration management. By allowing administrators to create, compare, and potentially restore a shadow copy of the CIB, it provides an additional layer of safety and change control in managing Pacemaker clusters.

If you plan to use crm_shadow, be sure to consult your crmsh version’s help documentation and test its functionality in a controlled setting before relying on it in production.