Pluggable Protection Provider¶

https://blueprints.launchpad.net/karbor/+spec/protection-plugin-is-design

Protection Provider¶

Protection Provider is a user-facing, configurable, pluggable entity, that supplies the answer for the questions: “how to” and “where to”. By composing different bank-store (responsible for the “where to”) and different Protection Plugins (each responsible for the “how to”). The Protection Provider is configurable, both in the terms of bank and protection plugins composition, and in their configuration.

The protection provider will contain internally, a map between any registered Protectable (OpenStack resource type) and a corresponding Protection Plugin, which is used for operations related to any appropriate resource.

There are 3 resource operations a Protection Provider supports, and any Protection Plugin needs to implement. These operations usually act on numerous resources, and the Protection Provider infrastructure is responsible for using the corresponding Protection Plugin implementation, for each resource. The Protection Provider is responsible for initiating a DFS traverse of the resource graph, building tasks for each of the resources, and linking them in respect of the execution order and dependency.

Protect: the protection provider will traverse the selected resources from the resource graph
Restore: the protection provider will traverse the resource graph saved in the checkpoint
Delete: the protection provider will traverse the resource graph saved in the checkpoint

After the entire graph has been traversed, the Protection Provider will return the task flow which will be queued and then executed according to the executor’s policy. When all the tasks are done the operation is considered complete.

Protection Provider Configuration¶

Protection Providers are loaded from configuration files, placed in the directory specified by the provider_config_dir configuration option (by default: /etc/karbor/providers.d). Each provider configuration file must bear the .conf suffix and contain a [provider] section. This section specifies the following configuration:

name: the display name of the protection provider
id: unique identifier
description: textual description
bank: path to the bank plugin
plugin: path to a protection plugin. Should be specified multiple times for multiple protection plugins. Every Protectable must have a corresponding Protection Plugin to support it.

Additionally, the provider configuration file can include other section (besides the [provider] section), to be used as configuration for each bank or protection plugin.

For example:

[provider]
name = Foo
id = 2e0c8826-81d6-44f5-bbe5-8f46a98c5845
description = Example Protection Provider
bank = karbor.protections.karbor-swift-bank-plugin
plugin = karbor.protections.karbor-volume-protection-plugin
plugin = karbor.protections.karbor-image-protection-plugin
plugin = karbor.protections.karbor-server-protection-plugin
plugin = karbor.protections.karbor-project-protection-plugin

[swift_client]
bank_swift_auth_url = http://10.0.0.10:5000
bank_swift_user = admin
bank_swift_key = password

Protection Plugin¶

A Protection Plugin is a component responsible for the implementation of operations (protect, restore, delete) of one or more Protectable (i.e resource type). When writing a Protection Plugin, the following needs to be defined:

Which resources does the protection plugin support
What is the schema of parameters for each operation
What is the schema of information the protection plugin stores in a Checkpoint
The implementation of each operation

Protection Plugin API & Workflow¶

Protection Plugin defines how to protect, restore, and delete resources.

When performing an operation there might be a need for a ProtectionPlugin to perform actions on a resource before or after some operation was performed on a related resource.

For example, before takin a spanshot of a volume you need to quiesce the VM andor run any guest agent operation. Doing it after taking the checkpoint is useless.

On the other hand, when copying a volume’s data to different sites there is no need for other operations to wait on the copy.

Finally, there might be a need to perform an operation marking a transaction as successful after everything related to a VM was protected.

Looking at this we see there are 3 distinct phases for every protection.

Preparation Phase: This phase for performing actions in relation to a resource’s dependencies. It’s called the “Preparation Phase” because it where a plugin should do all the preparation required for the next phase. Operation in this phase should be as short as possible since they are not parraralized as much as in the following phases. As an example, taking snapshots of all the volumes should happen in relation to the owning VMs and also happen in a narrower time frame. Copying those snapshots can happen later and is much more parallizable.
Main Phase: This phase is for doing work that has no dependencies or time sensitivity. This will be mainly used for transferring the large amount of information generated in the backup to different sites.
Completion Phase: This phase is for performing work once all the work, not just preparation, was completed on a resource and all of it’s dependencies. This is a good place to attach resources (in case of restore) or close transactions.

As a Protection Plugin developer you want to minimize the work needed to be done in the preparation and completion phases and do the bulk of the work in the main phase since will allow for the most efficient execution of the operation.

It’s important to note that a developer doesn’t have to do any action during a phase. It’s completely valid to only use the main or preparation phase. In fact, we think it’s going to be very rare that a Protection Plugin will need to use all the phases.

In order to specify the detailed flow of each operation, a Protection Plugin needs to implement numerous ‘hooks’. These hooks, differ from one another by their time of execution in respect to other hooks, either of the same resource, or other resources.

For each operation the pluggin can implement each of the hooks:

Preparation hooks: as noted, preparation is for running tasks in relation to other resources in the graph. This is why two hooks exist, one for running before dependent resources’ pereperation and one for after.
1. Prepare begin hook: invoked before any hook of this resource and dependent resources has begun.
  
  For tasks that need to happen before any dependent resource’s operations begin
  
  Hook method name: on_prepare_begin
2. Prepare finish hook: invoked after any prepare hooks of dependent resources are complete.
  
  For tasks that finish the work began in prepare begin hook, for tasks that require that the dependent resource’s prepare phase finished
  
  Hook method name: on_prepare_finish
Main hook: invoked after the resource prepare hooks are complete.

For tasks that do heavy lifting and can run in parallel to dependent or dependee resources main hooks

Hook method name: on_main
Complete hook: invoked once the resource’s main hook is complete, and the dependent resources’ complete hooks are complete

For tasks that require that the dependent resource’s operations are complete, and finalize the operation on the resource.

Hook method name: on_complete

For example: a Protection Plugin for Nova servers, might implement a protect operation by using prepare begin hook to quiesce the Server and/or contact a guest agent to complete transactions. A protection plugin for Cinder volumes can implement prepare finish hook to take a snapshot of the volume. The server’s prepare finish hook unquiesces the server and/or contacts a guest agent. Both the server’s and the volume’s main hook do the heavy lifting of copying the data.

Notes:

Unimplemented methods are practically no-op
Each such method receives as parameters: checkpoint, context, resource, and parameters objects

def prepare_finish(self, checkpoint, context, resource, parameters):
    ...

Protection Plugin Hooks¶

Green: Child resource Prepare_begin depends on its parent resource Prepare_begin

Indigo: The resource Prepare_finish depends on the resource Prepare_begin

Purple: Parent resource Prepare_finish depends on the child resource Prepare_finish

Yellow: The resource Main depends on the resource Prepare_finish

Red: The resource Complete depends on the resource Main

Black: Parent resource Complete depends on the child resource’s Complete

This scheme decouples the tree structure from the task execution. A plugin that handles multiple resources or that aggregates multiple resources to one task can use this mechanism to only return tasks when appropriate for it’s scheme.