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Centralized Plugin Discovery and Distribution

The Tanzu CLI uses a system of plugins to provide functionality to interact with different Tanzu products. Plugins are stored and discovered from "plugin discovery sources".

To install a plugin, the CLI uses an OCI discovery source, which contains the inventory of plugins including metadata for each plugin. This plugin inventory also includes the location from which a plugin's binary can be downloaded.

The below figure illustrates such an OCI discovery.

Centralized Plugin Discovery/Distribution

Plugin Binary Storage

The above figure depicts a joint approach to Discovery and Distribution of plugins, where the plugin binaries are stored in the same OCI registry as the the plugin inventory. However, such a co-location is not technically required, and the plugin binaries could be stored in a separate OCI registry.

Plugin Inventory Database

The inventory of plugins is stored in an SQLite database file, which in turn is stored as an OCI image in the OCI registry. When the Tanzu CLI needs to obtain information on available plugins, be it for the tanzu plugin search command to list plugins to the user, or for the tanzu plugin install command to actually obtain information to install a plugin, the CLI does the following:

  1. Verify the signature of the OCI image containing the SQLite DB file, and if successful,
  2. Pull the OCI image, extracting at the same time the SQLite DB file.

The CLI then uses SQLite queries to obtain the desired information about one or more plugins. Using that information, the CLI can either list plugins to the user, or proceed to install plugins.

Plugin Inventory Cache

Pulling the plugin inventory OCI image takes a noticeable amount of time for the CLI. Therefore, to keep the CLI quick and responsive, the plugin inventory DB is cached under $HOME/.cache/tanzu/plugin_inventory/default and the CLI uses this cache whenever it needs to query the DB. This cache has a time-to-live of 30 minutes, which means that a CLI could at most require 30 minutes to become aware of new plugins published to the central repository of plugins.

If for some reason a user wants to force an immediate refresh of the plugin inventory cache, they can run the tanzu plugin source init command. To refresh the plugin inventory DB, the CLI first compares the digest of the remote OCI image with the digest stored in the cache; if the digests match, the DB need not be downloaded and is considered to have been refreshed, which resets the TTL.

Plugin Groups

Plugin groups define a list of plugin/version combinations that are applicable together. Plugin groups aim to facilitate an efficient installation of sets of plugins that pertain to a particular product that a user wants to interact with.

Plugin groups are stored in the same SQLite DB as plugins and the CLI proceeds in the same fashion to obtain plugin group information for the tanzu plugin group search and tanzu plugin install --group <groupName>:<groupVersion> commands.

SQlite database schemas

The database schema used for the plugin inventory and the one for the plugin group inventory can be seen in the pkg/plugininventory/data/sqlite/create_tables.sql file within this repository.