Summary

Adding quota settings to snapshots is crucial for enhancing node stability. Currently, various snapshot types exist, and to simplify implementation and reduce complexity in specific snapshot implementations, it is recommended to centralize quota processing at the core layer. This proposal outlines a universal snapshot quota support mechanism.

Goals

• Universal snapshot support for quota: To implement a unified approach for managing quotas across all snapshot types.

Proposal

This proposal introduces modifications to the snapshotter interface and data structures to enable universal quota support. The changes are focused on the core snapshot layer to ensure consistency and simplify individual snapshot implementations.

Interface and Data Structure Modifications

1. Snapshotter Interface Enhancement:

   Add a new interface to the snapshotter to explicitly declare quota support capability:

   // SupportedQuota indicates whether quotas are supported or not by the snapshotter.
   SupportedQuota() bool

   This interface method, SupportedQuota(), will return a boolean value indicating whether the specific snapshotter implementation supports quota settings.

2. creatContainer API Extension:

   Extend the creatContainer API within the CRI (Container Runtime Interface) with a new field named 'storage'. This field will be part of the container creation request and will contain the following internal data structures to handle quota settings:

   storage: {
       ignoreFailed: bool, // Indicates whether to ignore failure if quota setting is not supported.
       size: string,       // Represents the storage quota size. Use string to differentiate between unset and '0'.
   }

   • ignoreFailed: A boolean type field. If set to true, the system will ignore failures that occur when attempting to set quotas on a snapshotter that does not support them.
   • size: A string type field representing the storage quota size. Using a string type ensures a clear distinction between an unset quota value (empty string '') and a quota size explicitly set to zero ('0').

Core Snapshot Quota Handling Steps

When the storage field with a size parameter is provided during snapshot creation, the core snapshot layer will follow these steps:

1. Check Snapshotter Quota Support: Invoke the SupportedQuota() method of the snapshotter implementation to determine if it supports quota settings.

2. Quota Setting Based on Support and ignoreFailed:

   • If the snapshotter supports quotas (SupportedQuota() returns true): The core layer will proceed to set the quota label for the snapshot using the provided size.

   • If the snapshotter does not support quotas (SupportedQuota() returns false):

     • If ignoreFailed is set to true: The core layer will take no action regarding quota setting and proceed with snapshot creation, effectively ignoring the quota request.

     • If ignoreFailed is set to false: The core layer will indicate a failure in the snapshot creation process, as a quota was requested but cannot be fulfilled by the underlying snapshotter, and the ignoreFailed policy is not set to permit ignoring this failure.

Specific Snapshot Implementation Requirements

Individual snapshot implementations are expected to adhere to the following:

1. Quota Setting Error Handling: If a specific snapshot implementation fails to set the quotasize (for reasons such as limitations of the underlying storage driver), it must return an appropriate error to the core layer. This error will be propagated to the user, indicating that the quota setting was unsuccessful for that specific snapshot.

By centralizing the quota handling logic at the core layer and providing clear interfaces, this design promotes a more stable and manageable node environment.

/cc @dmcgowan @mikebrow