--- layout: docs page_title: Plugin System description: Learn about Vault's plugin system. --- # Plugin System All Vault auth and secret backends are considered plugins. This simple concept allows both built-in and external plugins to be treated like Legos. Any plugin can exist at multiple different locations. Different versions of a plugin may be at each one, with each version differing from Vault's version. ## Built-In Plugins Built-in plugins are shipped with Vault, often for commonly used implementations, and require no additional operator intervention to run. Built-in plugins are just like any other backend code inside Vault. To use a different or edited version of a built-in plugin, you would first edit the plugin's code or navigate to the Vault version holding the version of the plugin you desire. Then, you'd `$ cd` into the `cmd/:plugin-name` directory contained alongside that plugin's code. For instance, for AppRole, you would: `$ cd vault/builtin/credential/approle/cmd/approle`. Once in that directory, you would run `$ go build` to obtain a new binary for the AppRole plugin. Then you would add it to the plugin catalog as per normal, and enable it. # Plugin Architecture Vault's plugins are completely separate, standalone applications that Vault executes and communicates with over RPC. This means the plugin process does not share the same memory space as Vault and therefore can only access the interfaces and arguments given to it. This also means a crash in a plugin can not crash the entirety of Vault. It is possible to enable a custom plugin with a name that's identical to a built-in plugin. In such a situation, Vault will always choose the custom plugin when enabling it. ## Plugin Lifecycle Vault plugins are long-running processes that remain running once they are spawned by Vault, the parent process. Plugin processes can be started by Vault's active node and performance standby nodes. Additionally, there are cases where plugin processes may be terminated by Vault. These cases include but are not limited to: - Vault active node step-down - Vault barrier seal - Vault graceful shutdown - Disabling a Secrets Engine or Auth method that uses external plugins - Database configured connection deletion - Database configured connection update - Database configured connection reset request - Database root credentials rotation - WAL Rollback from a previously failed root credentials rotation operation The lifecycle of plugin processes are managed automatically by Vault. Termination of these processes are typical in certain scenarios, such as the ones listed above. Vault will start plugin processes when needed, typically by lazily loading the plugin when a request that requires the plugin is received by Vault. A plugin process may be started or terminated through other internal processes within Vault as well. Since Vault manages and tracks the lifecycle of its plugins, these processes should not be terminated by anything other than Vault. ## Plugin Communication Vault creates a mutually authenticated TLS connection for communication with the plugin's RPC server. While invoking the plugin process, Vault passes a [wrapping token](/docs/concepts/response-wrapping) to the plugin process' environment. This token is single use and has a short TTL. Once unwrapped, it provides the plugin with a uniquely generated TLS certificate and private key for it to use to talk to the original Vault process. The [`api_addr`][api_addr] must be set in order for the plugin process to establish communication with the Vault server during mount time. If the storage backend has HA enabled and supports automatic host address detection (e.g. Consul), Vault will automatically attempt to determine the `api_addr` as well. ~> Note: Reading the original connection's TLS connection state is not supported in plugins. ## Plugin Registration An important consideration of Vault's plugin system is to ensure the plugin invoked by Vault is authentic and maintains integrity. There are two components that a Vault operator needs to configure before external plugins can be run, the plugin directory and the plugin catalog entry. ### Plugin Directory The plugin directory is a configuration option of Vault, and can be specified in the [configuration file](/docs/configuration). This setting specifies a directory in which all plugin binaries must live; _this value cannot be a symbolic link_. A plugin can not be added to Vault unless it exists in the plugin directory. There is no default for this configuration option, and if it is not set plugins can not be added to Vault. ~> Warning: A Vault operator should take care to lock down the permissions on this directory to ensure a plugin can not be modified by an unauthorized user between the time of the SHA check and the time of plugin execution. ### Plugin Catalog The plugin catalog is Vault's list of approved plugins. The catalog is stored in Vault's barrier and can only be updated by a Vault user with sudo permissions. Upon adding a new plugin, the plugin name, SHA256 sum of the executable, and the command that should be used to run the plugin must be provided. The catalog will make sure the executable referenced in the command exists in the plugin directory. When added to the catalog the plugin is not automatically executed, it instead becomes visible to backends and can be executed by them. For more information on the plugin catalog please see the [Plugin Catalog API docs](/api/system/plugins-catalog). An example of plugin registration in current versions of Vault: ```shell-session $ vault plugin register -sha256= \ secret \ # type myplugin-database-plugin Success! Registered plugin: myplugin-database-plugin ``` Vault versions prior to v0.10.4 lacked the `vault plugin` operator and the registration step for them is: ```shell-session $ vault write sys/plugins/catalog/database/myplugin-database-plugin \ sha256= \ command="myplugin" Success! Data written to: sys/plugins/catalog/database/myplugin-database-plugin ``` ### Plugin Execution When a backend wants to run a plugin, it first looks up the plugin, by name, in the catalog. It then checks the executable's SHA256 sum against the one configured in the plugin catalog. Finally Vault runs the command configured in the catalog, sending along the JWT formatted response wrapping token and mlock settings. Like Vault, plugins support [the use of mlock when available](/docs/configuration#disable_mlock). ~> Note: If Vault is configured with `mlock` enabled, then the Vault executable and each plugin executable in your [plugins directory](/docs/internals/plugins#plugin-directory) must be given the ability to use the `mlock` syscall. ### Plugin Upgrades Plugins may be updated by registering and reloading them. More details on the upgrade procedure can be found in [Upgrading Vault Plugins](/docs/upgrading/plugins). ### Troubleshooting #### Unrecognized remote plugin message If the following error is encountered when enabling a plugin secret engine or auth method: ```sh Unrecognized remote plugin message: This usually means that the plugin is either invalid or simply needs to be recompiled to support the latest protocol. ``` Verify whether the Vault process has `mlock` enabled, and if so run the following command against the plugin binary: ```sh sudo setcap cap_ipc_lock=+ep ``` # Plugin Development ~> Advanced topic! Plugin development is a highly advanced topic in Vault, and is not required knowledge for day-to-day usage. If you don't plan on writing any plugins, we recommend not reading this section of the documentation. Because Vault communicates to plugins over a RPC interface, you can build and distribute a plugin for Vault without having to rebuild Vault itself. This makes it easy for you to build a Vault plugin for your organization's internal use, for a proprietary API that you don't want to open source, or to prototype something before contributing it back to the main project. In theory, because the plugin interface is HTTP, you could even develop a plugin using a completely different programming language! (Disclaimer, you would also have to re-implement the plugin API which is not a trivial amount of work.) Developing a plugin is simple. The only knowledge necessary to write a plugin is basic command-line skills and basic knowledge of the [Go programming language](http://golang.org). Your plugin implementation needs to satisfy the interface for the plugin type you want to build. You can find these definitions in the docs for the backend running the plugin. ```go package main import ( "os" myPlugin "your/plugin/import/path" "github.com/hashicorp/vault/api" "github.com/hashicorp/vault/sdk/plugin" ) func main() { apiClientMeta := &api.PluginAPIClientMeta{} flags := apiClientMeta.FlagSet() flags.Parse(os.Args[1:]) tlsConfig := apiClientMeta.GetTLSConfig() tlsProviderFunc := api.VaultPluginTLSProvider(tlsConfig) err := plugin.Serve(&plugin.ServeOpts{ BackendFactoryFunc: myPlugin.Factory, TLSProviderFunc: tlsProviderFunc, }) if err != nil { logger := hclog.New(&hclog.LoggerOptions{}) logger.Error("plugin shutting down", "error", err) os.Exit(1) } } ``` And that's basically it! You would just need to change `myPlugin` to your actual plugin. For more information on how to register and enable your plugin, check out the [Building Plugin Backends](https://learn.hashicorp.com/vault/developer/plugin-backends) tutorial. [api_addr]: /docs/configuration#api_addr