velero/docs/plugins.md

# Plugins

Velero has a plugin architecture that allows users to add their own custom functionality to Velero backups & restores 
without having to modify/recompile the core Velero binary. To add custom functionality, users simply create their own binary 
containing implementations of Velero's plugin kinds (described below), plus a small amount of boilerplate code to 
expose the plugin implementations to Velero. This binary is added to a container image that serves as an init container for 
the Velero server pod and copies the binary into a shared emptyDir volume for the Velero server to access. 

Multiple plugins, of any type,  can be implemented in this binary.

A fully-functional [sample plugin repository][1] is provided to serve as a convenient starting point for plugin authors.

## Plugin Kinds

Velero currently supports the following kinds of plugins:

- **Object Store** - persists and retrieves backups, backup logs and restore logs
- **Volume Snapshotter** - creates volume snapshots (during backup) and restores volumes from snapshots (during restore)
- **Backup Item Action** - executes arbitrary logic for individual items prior to storing them in a backup file
- **Restore Item Action** - executes arbitrary logic for individual items prior to restoring them into a cluster

## Plugin Logging

Velero provides a [logger][2] that can be used by plugins to log structured information to the main Velero server log or 
per-backup/restore logs. It also passes a `--log-level` flag to each plugin binary, whose value is the value of the same 
flag from the main Velero process. This means that if you turn on debug logging for the Velero server via `--log-level=debug`, 
plugins will also emit debug-level logs. See the [sample repository][1] for an example of how to use the logger within your plugin.



[1]: https://github.com/heptio/velero-plugin-example
[2]: https://github.com/heptio/velero/blob/master/pkg/plugin/logger.go