Event notifications development in Vault plugins

Event notifications can provide useful information from your plugin that might be helpful to operators and clients of Vault clusters. Any plugin running in Vault Enterprise 1.16+ can generate such events.

This article assumes that the plugin is written in the Go programming language. It is possible for non-Go plugins to send events as well by calling the SendEvent gRPC call directly.

Sending event notifications in plugins

Sending event notifications within a plugin is as simple as calling:

err := logical.SendEvent(ctx, b, eventType, metadata...)

where:

• ctx is a context.Context interface that is currently unused,
• b is your plugin backend, which implements the logical.EventSender interface,
• eventType is a string for your event type,
• metadata is a list of strings, which are interpreted as pairs that will be added to the event notification metadata, e.g., metadata := []string{"key1", "value1", "key2", "value2"} means that the metadata will include the pairs key1: value1 and key2: value2, and,
• logical refers to github.com/hashicorp/vault/sdk/logical.

logical.SendEvent is non-blocking and sends the event notifications asynchronously.

Best practices

While there are no strict rules for what events a plugin may generate, there are some best practices to follow:

• Do not include sensitive or secret data in the event notification. Events are not protected by the same policy as the underlying secret.

• Only generate event notificiations on writes and actionable errors, not reads. Generally, reads are more frequent than writes so generating event notifications for every read operation could have a negative impact on the server performance. Operators that need to be notified when information is read are usually better served by using Vault audit logs.

• Prefix event types with your plugin name to avoid clashing with other plugins' event types. For example, the database plugin uses the database/ prefix for all of its event notifications.

• Use common metadata keys, such as data_path for the API path to the secret the event notification is about, and operation to indicate what modification took place.

• Document the event types that your plugin produces, including descriptions of when those are generated.

• Use logical.SendEvent() to send event notifications. Although it is possible to call the framework.Backend or gRPC methods directly to send event notifications, logical.SendEvent abstracts away much of that for you.

• Send event notifications at the end of your methods, or in a defer, to ensure that the event notification has the most up-to-date information.

• Fail gracefully if the event notification system is unavailble. This is detected as an error when sending events, such as framework.ErrNoEvents, which usually occurs when running on older versions of Vault where event notifications are not present or have been disabled.

• Generate events in all editions of Vault. Even though it is not possible to subscribe to event notifications in the Community Edition of Vault, plugins are generally unaware of what edition of Vault they are connected to and should generate events regardless.

Examples

Here are some examples of adding event notifications to the KV and database plugins in Vault:

• https://github.com/hashicorp/vault-plugin-secrets-kv/pull/88
• https://github.com/hashicorp/vault/pull/24718