BackupItemAction v2 design

This includes necessary changes to support async item action monitoring.

Signed-off-by: Scott Seago <[email protected]>

design/biav2-design.md

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+# Design for BackupItemAction v2 API
+
+## Abstract
+This design includes the changes to the BackupItemAction (BIA) api design as required by the [Item Action Progress Monitoring](general-progress-monitoring.md) feature.
+The BIA v2 interface will have two new methods, and the Execute() return signature will be modified.
+If there are any additional BIA API changes that are needed in the same Velero release cycle as this change, those can be added here as well.
+
+## Background
+This API change is needed to facilitate long-running plugin actions that may not be complete when the Execute() method returns.
+It is an optional feature, so plugins which don't need this feature can simply return an empty operation ID and the new methods can be no-ops.
+This will allow long-running plugin actions to continue in the background while Velero moves on to the next plugin, the next item, etc.
+
+## Goals
+- Allow for BIA Execute() to optionally initiate a long-running operation and report on operation status.
+
+## Non Goals
+- Allowing velero control over when the long-running operation begins.
+
+
+## High-Level Design
+As per the [Plugin Versioning](plugin-versioning.md) design, a new BIAv2 plugin `.proto` file will be created to define the GRPC interface.
+v2 go files will also be created in `plugin/clientmgmt/backupitemaction` and `plugin/framework/backupitemaction`, and a new PluginKind will be created.
+The velero Backup process will be modified to reference v2 plugins instead of v1 plugins.
+An adapter will be created so that any existing BIA v1 plugin can be executed as a v2 plugin when executing a backup.
+
+## Detailed Design
+
+### proto changes (compiled into golang by protoc)
+
+The v2 BackupItemAction.proto will be like the current v1 version with the following changes:
+ExecuteResponse gets a new field:
+```
+message ExecuteResponse {
+    bytes item = 1;
+    repeated generated.ResourceIdentifier additionalItems = 2;
+    string operationID = 3;
+}
+```
+The BackupItemAction service gets two new rpc methods:
+```
+service BackupItemAction {
+    rpc AppliesTo(BackupItemActionAppliesToRequest) returns (BackupItemActionAppliesToResponse);
+    rpc Execute(ExecuteRequest) returns (ExecuteResponse);
+    rpc Progress(BackupItemActionProgressRequest) returns (BackupItemActionProgressResponse);
+    rpc Cancel(BackupItemActionCancelRequest) returns (google.protobuf.Empty);
+}
+```
+To support these new rpc methods, we define new request/response message types:
+```
+message BackupItemActionProgressRequest {
+    string plugin = 1;
+    string operationID = 2;
+    bytes backup = 3;
+}
+
+message BackupItemActionProgressResponse {
+    generated.OperationProgress progress = 1;
+}
+
+message BackupItemActionCancelRequest {
+    string plugin = 1;
+    string operationID = 2;
+    bytes backup = 3;
+}
+
+```
+One new shared message type will be added, as this will also be needed for v2 RestoreItemAction and VolmeSnapshotter:
+```
+message OperationProgress {
+    bool completed = 1;
+    string err = 2;
+    int64 itemsCompleted = 3;
+    int64 itemsToComplete = 4;
+    google.protobuf.Timestamp started = 5;
+    google.protobuf.Timestamp updated = 6;
+}
+```
+
+A new PluginKind, `BackupItemActionV2`, will be created, and the backup process will be modified to use this plugin kind.
+See [Plugin Versioning](plugin-versioning.md) for more details on implementation plans, including v1 adapters, etc.
+
+
+## Compatibility
+The included v1 adapter will allow any existing BackupItemAction plugin to work as expected, with an empty operation ID returned from Execute() and no-op Progress() and Cancel() methods.
+
+## Implementation
+This will be implemented during the Velero 1.11 development cycle.