Design doc for upload progress monitoring (vmware-tanzu#3416)

Change to add new plugin SnapshotItemAction, added started/updated fields to UploadProgress
Updated SnapshotItemAction, added additional tasks

Signed-off-by: Dave Smith-Uchida <[email protected]>

design/upload-progress.md

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+# Upload Progress Monitoring
+
+Volume snapshotter plug-in are used by Velero to take snapshots of persistent volume contents. 
+Depending on the underlying storage system, those snapshots may be available to use immediately, 
+they may be uploaded to stable storage internally by the plug-in or they may need to be uploaded after
+the snapshot has been taken. We would like for Velero to continue on to the next part of the backup as quickly
+as possible but we would also like the backup to not be marked as complete until it is a usable backup.  We'd also
+eventually like to bring the control of upload under the control of Velero and allow the user to make decisions
+about the ultimate destination of backup data independent of the storage system they're using.
+
+
+
+## Examples
+AWS - AWS snapshots return quickly, but are then uploaded in the background and cannot be used until EBS moves
+the data into S3 internally.
+
+vSphere - The vSphere plugin takes a local snapshot and then the vSphere plugin uploads the data to S3.  The local
+snapshot is usable before the upload completes.
+
+Restic - Does not go through the volume snapshot path.  Restic backups will block Velero progress until completed.
+
+## Goals
+
+- Enable monitoring of operations that continue after snapshotting operations have completed
+- Keep non-usable backups (upload/persistence has not finished) from appearing as completed
+- Minimize change to volume snapshot and BackupItemAction plug-ins
+
+## Non-goals
+- Unification of BackupItemActions and VolumeSnapshotters
+
+## Models
+
+### Internal configuration and management
+In this model, movement of the snapshot to stable storage is under the control of the snapshot
+plug-in.  Decisions about where and when the snapshot gets moved to stable storage are not
+directly controlled by Velero.  This is the model for the current VolumeSnapshot plugins.
+
+### Velero controlled management
+In this model, the snapshot is moved to external storage under the control of Velero.  This
+enables Velero to move data between storage systems.  This also allows backup partners to use
+Velero to snapshot data and then move the data into their backup repository.
+
+## Backup phases
+
+Velero currently has backup phases "InProgress" and "Completed".  The backup moves to the Completed
+phase when all of the volume snapshots have completed and the Kubernetes metadata has been written
+into the object store.  However, the actual data movement may be happening in the background
+after the backup has been marked "Completed".  The backup is not actually a stable backup until
+the data has been persisted properly.  In some cases (e.g. AWS) the backup cannot be restored from
+until the snapshots have been persisted.
+
+Once the snapshots have been taken, however, it is possible for additional backups to be made without
+interference.  Waiting until all data has been moved before starting the next backup will
+slow the progress of the system without adding any actual benefit to the user.
+
+A new backup phase, "Uploading" will be introduced.  When a backup has entered this phase, Velero
+is free to start another backup.  The backup will remain in the "Uploading" phase until all data
+has been successfully moved to persistent storage.  The backup will not fail once it reaches
+this phase, it will continuously retry moving the data.  If the backup is deleted (cancelled), the plug-ins will
+attempt to delete the snapshots and stop the data movement - this may not be possible with all
+storage systems.
+
+### State progression
+
+![image](UploadFSM.png)
+### New
+When a backup request is initially created, it is in the "New" phase.  
+
+The next state is either "InProgress" or "FailedValidation"
+
+### FailedValidation
+If the backup request is incorrectly formed, it goes to the "FailedValidation" phase and terminates
+
+### InProgress
+When work on the backup begins, it moves to the "InProgress" phase.  It remains in the "InProgress"
+phase until all pre/post execution hooks have been executed, all snapshots have been taken and the
+Kubernetes metadata and backup info is safely written to the object store plug-in.
+
+In the current implementation, Restic backups will move data during the "InProgress" phase.
+In the future, it may be possible to combine a snapshot with a Restic (or equivalent) backup which
+would allow for data movement to be handled in the "Uploading" phase,
+
+The next phase is either "Completed", "Uploading", "Failed" or "PartiallyFailed".  Backups which 
+would have a final phase of "Completed" or "PartiallyFailed" may move to the "Uploading" state.
+A backup which will be marked "Failed" will go directly to
+the "Failed" phase.  Uploads may continue in the background for snapshots that were taken by a "Failed"
+backup, but no progress will not be monitored or updated.  When a "Failed" backup is deleted, all snapshots
+will be deleted and at that point any uploads still in progress should be aborted.
+
+### Uploading (new)
+The "Uploading" phase signifies that the main part of the backup, including snapshotting has completed successfully
+and and uploading is continuing.  In the event of an error during uploading, the phase will change to 
+UploadingPartialFailure.  On success, the phase changes to Completed.  The backup cannot be
+restored from when it is in the Uploading state.
+
+### UploadingPartialFailure (new)
+The "UploadingPartialFailure" phase signifies that the main part of the backup, including snapshotting has completed,
+but there were partial failures either during the main part or during the uploading.  The backup cannot be
+restored from when it is in the UploadingPartialFailure state.
+
+### Failed
+When a backup has had fatal errors it is marked as "Failed"  This backup cannot be restored from.
+
+### Completed
+The "Completed" phase signifies that the backup has completed, all data has been transferred to stable storage
+and the backup is ready to be used in a restore.  When the Completed phase has been reached it is safe
+to remove any of the items that were backed up.
+
+### PartiallyFailed
+The "PartiallyFailed" phase signifies that the backup has completed and at least part of the backup is usable.
+Restoration from a PartiallyFailed backup will not result in a complete restoration but pieces may be available.
+
+## Workflow
+
+When a BackupAction is executed, any SnapshotItemAction or VolumeSnapshot plugins will return snapshot IDs.
+The plugin should be able to provide status on
+the progress for the snapshot and handle cancellation of the upload if the snapshot is deleted.
+If the plugin is restarted, the snapshot ID should remain valid.
+
+When all snapshots have been taken and Kubernetes resources have been persisted to the ObjectStorePlugin
+the backup will either have fatal errors or will be at least partially usable.
+
+If the backup has fatal errors it will move to the "Failed" state and finish. If a backup fails, the upload will not be
+cancelled but it will not be monitored either.  For backups in any phase, all snapshots will be deleted when the backup
+is deleted.  Plugins will cancel any data movement and
+remove snapshots and other associated resources when the VolumeSnapshotter DeleteSnapshot method or 
+DeleteItemAction Execute method is called.
+
+Velero will poll the plugins for status on the snapshots when the backup exits the "InProgress" phase and
+has no fatal errors.
+
+If any snapshots are not complete, the backup will move to either Uploading or UploadingPartialFailure or Failed.
+
+Post-snapshot operations may take a long time and Velero and its plugins may be restarted during 
+this time.  Once a backup has moved into the Uploading or UploadingPartialFailure phase, another 
+backup may be started.
+
+While in the Uploading or UploadingPartialFailure phase, the snapshots and backup items will be periodically polled.
+When all of the snapshots and backup items have reported success, the backup will move to the Completed or 
+PartiallyFailed phase, depending on whether the backup was in the Uploading or UploadingPartialFailure phase.
+
+The Backup resources will not be written to object storage until the backup has entered a final phase: 
+Completed, Failed or PartialFailure
+## Reconciliation of InProgress backups
+
+InProgress backups will not have a `velero-backup.json` present in the object store.  During reconciliation, backups which
+do not have a `velero-backup.json` object in the object store will be ignored.
+
+## Plug-in API changes
+
+### UploadProgress struct
+
+    type UploadProgress struct {
+        completed bool                          // True when the operation has completed, either successfully or with a failure
+        err error                               // Set when the operation has failed
+        itemsCompleted, itemsToComplete int64   // The number of items that have been completed and the items to complete
+                                                // For a disk, an item would be a byte and itemsToComplete would be the
+                                                // total size to transfer (may be less than the size of a volume if
+                                                // performing an incremental) and itemsCompleted is the number of bytes
+                                                // transferred.  On successful completion, itemsCompleted and itemsToComplete
+                                                // should be the same
+        started, updated time.Time              // When the upload was started and when the last update was seen.  Not all
+                                                // systems retain when the upload was begun, return Time 0 (time.Unix(0, 0))
+                                                // if unknown.
+    }
+
+### VolumeSnapshotter changes
+
+A new method will be added to the VolumeSnapshotter interface (details depending on plug-in versioning spec)
+
+    UploadProgress(snapshotID string) (UploadProgress, error)
+
+UploadProgress will report the current status of a snapshot upload.  This should be callable at any time after the snapshot
+has been taken.  In the event a plug-in is restarted, if the snapshotID continues to be valid it should be possible to
+retrieve the progress.
+
+`error` is set if there is an issue retrieving progress.  If the snapshot is has encountered an error during the upload,
+the error should be return in UploadProgress and error should be nil.
+
+### SnapshotItemAction plug-in
+
+Currently CSI snapshots and the Velero Plug-in for vSphere are implemented as BackupItemAction plugins.  The majority of
+BackupItemAction plugins do not take snapshots or upload data so rather than modify BackupItemAction we introduce a new
+plug-ins, SnapshotItemAction.  SnapshotItemAction will be used in place of BackupItemAction for
+the CSI snapshots and the Velero Plug-in for vSphere and will return a snapshot ID in addition to the item itself.
+
+The SnapshotItemAction plugin identifier as well as the Item and Snapshot ID will be stored in the 
+`<backup-name>-itemsnapshots.json.gz`.  When checking for progress, this info will be used to select the appropriate
+SnapshotItemAction plugin to query for progress.
+
+_NotApplicable_ should only be returned if the SnapshotItemAction plugin should not be handling the item.  If the
+SnapshotItemAction plugin should handle the item but, for example, the item/snapshot ID cannot be found to report progress, a
+UploadProgress struct with the error set appropriately (in this case _NotFound_) should be returned.
+
+    // SnapshotItemAction is an actor that snapshots an individual item being backed up (it may also do other
+    operations on the item that is returned).
+
+    type SnapshotItemAction interface {
+    	// AppliesTo returns information about which resources this action should be invoked for.
+    	// A BackupItemAction's Execute function will only be invoked on items that match the returned
+    	// selector. A zero-valued ResourceSelector matches all resources.
+    	AppliesTo() (ResourceSelector, error)
+
+    	// Execute allows the ItemAction to perform arbitrary logic with the item being backed up,
+    	// including mutating the item itself prior to backup. The item (unmodified or modified)
+    	// should be returned, along with an optional slice of ResourceIdentifiers specifying
+    	// additional related items that should be backed up.
+    	Execute(item runtime.Unstructured, backup *api.Backup) (runtime.Unstructured, snapshotID string,
+    	    []ResourceIdentifier, error)
+    	
+    	// Progress  
+    	Progress(input *SnapshotItemProgressInput) (UploadProgress, error)
+    }
+
+    // SnapshotItemProgressInput contains the input parameters for the SnapshotItemAction's Progress function.
+    type SnapshotItemProgressInput struct {
+    	// Item is the item that was stored in the backup
+    	Item runtime.Unstructured
+    	// SnapshotID is the snapshot ID returned by SnapshotItemAction
+    	SnapshotID string
+    	// Backup is the representation of the restore resource processed by Velero.
+    	Backup *velerov1api.Backup
+    }
+
+
+## Changes in Velero backup format
+
+No changes to the existing format are introduced by this change.  A `<backup-name>-itemsnapshots.json.gz` file will be 
+added that contains the items and snapshot IDs returned by ItemSnapshotAction.  Also, the creation of the 
+`velero-backup.json` object will not occur until the backup moves to one of the terminal phases (_Completed_, 
+_PartiallyFailed_, or _Failed_).  Reconciliation should ignore backups that do not have a `velero-backup.json` object.
+
+The cluster that is creating the backup will have the Backup resource present and will be able to manage the backup
+before the backup completes.
+
+If the Backup resource is removed (e.g. Velero is uninstalled) before a backup completes and writes its 
+`velero-backup.json` object, the other objects in the object store for the backup will be effectively orphaned.  This 
+can currently happen but the current window is much smaller.
+
+### `<backup-name>-itemsnapshots.json.gz`
+The itemsnapshots file is similar to the existing `<backup-name>-itemsnapshots.json.gz`  Each snapshot taken via
+SnapshotItemAction will have a JSON record in the file.  Exact format TBD.
+
+## CSI snapshots
+
+For systems such as EBS, a snapshot is not available until the storage system has transferred the snapshot to
+stable storage.  CSI snapshots expose the _readyToUse_ state that, in the case of EBS, indicates that the snapshot
+has been transferred to durable storage and is ready to be used.  The CSI BackupItemProgress.Progress method will
+poll that field and when completed, return completion.
+
+## vSphere plug-in
+
+The vSphere Plug-in for Velero uploads snapshots to S3 in the background.  This is also a BackupItemAction plug-in,
+it will check the status of the Upload records for the snapshot and return progress.
+
+## Backup workflow changes
+
+The backup workflow remains the same until we get to the point where the `velero-backup.json` object is written.
+At this point, we will queue the backup to a finalization go-routine.  The next backup may then begin.  The finalization
+routine will run across all of the volume snapshots and call the _UploadProgress_ method on each of them.  It will
+then run across all items and call _BackupItemProgress.Progress_ for any that match with a BackupItemProgress.
+
+If all snapshots and backup items have finished uploading (either successfully or failed), the backup will be completed
+and the backup will move to the appropriate terminal phase and upload the `velero-backup.json` object to the object store
+and the backup will be complete.
+
+If any of the snapshots or backup items are still being processed, the phase of the backup will be set to the appropriate
+phase (_Uploading_ or _UploadingPartialFailure_).  In the event of any of the upload progress checks return an error, the 
+phase will move to _UploadingPartialFailure_.  The backup will then be requeued and will be rechecked again after some 
+time has passed.
+
+## Restart workflow
+On restart, the Velero server will scan all Backup resources.  Any Backup resources which are in the _InProgress_ phase
+will be moved to the _Failed_ phase.  Any Backup resources in the _Oploading_ or _OploadingPartialFailure_ phase will
+be treated as if they have been requeued and progress checked and the backup will be requeued or moved to a terminal
+phase as appropriate.
+
+# Implementation tasks
+
+VolumeSnapshotter new plugin APIs  
+BackupItemProgress new plugin interface  
+New backup phases  
+Defer uploading `velero-backup.json`  
+AWS EBS plug-in UploadProgress implementation  
+Upload monitoring  
+Implementation of `<backup-name>-itemsnapshots.json.gz` file  
+Restart logic  
+Change in reconciliation logic to ignore backups that have not completed  
+CSI plug-in BackupItemProgress implementation  
+vSphere plug-in BackupItemProgress implementation (vSphere plug-in team)  
+
+# Future Fragile/Durable snapshot tracking
+Futures are here for reference, they may change radically when actually implemented.
+
+Some storage systems have the ability to provide different levels of protection for snapshots.  These are termed "Fragile"
+and "Durable".  Currently, Velero expects snapshots to be Durable (they should be able to survive the destruction of the
+cluster and the storage it is using).  In the future we would like the ability to take advantage of snapshots that are
+Fragile.  For example, vSphere snapshots are Fragile (they reside in the same datastore as the virtual disk).  The Velero
+Plug-in for vSphere uses a vSphere local/fragile snapshot to get a consistent snapshot, then uploads the data to S3 to
+make it Durable.  In the current design, upload progress will not be complete until the snapshot is ready to use and
+Durable.  It is possible, however, to restore data from a vSphere snapshot before it has been made Durable, and this is a
+capability we'd like to expose in the future.  Other storage systems implement this functionality as well.  We will be moving
+the control of the data movement from the vSphere plug-in into Velero.
+
+Some storage system, such as EBS, are only capable of creating Durable snapshots.  There is no usable intermediate Fragile stage.
+
+For a Velero backup, users should be able to specify whether they want a Durable backup or a Fragile backup (Fragile backups
+may consume less resources, be quicker to restore from and are suitable for things like backing up a cluster before upgrading
+software).  We can introduce three snapshot states - Creating, Fragile and Durable.  A snapshot would be created with a
+desired state, Fragile or Durable.  When the snapshot reaches the desired or higher state (e.g. request was for Fragile but
+snapshot went to Durable as on EBS), then the snapshot would be completed.