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Version: 1.x

HTTP KeyValue Watcher

This component demonstrates a Wasm-based system for monitoring and reacting to key-value store operations through HTTP interfaces. It integrates with wasi-http for handling Outgoing HTTP responses and wasi-keyvalue for key-value store interactions. The component establishes watch triggers based on link configuration and executes configurable reactions when events occur. At runtime, it links to a Redis-backed implementation of the key-value store interface.

Prerequisites​

  • cargo 1.75
  • wash 0.37.0

Building​

bash
wash build

Running with wasmCloud​

You can build and deploy your component with all dependencies and a hot reload loop with wash dev.

shell
wash dev

Note​

The watcher interface of the Redis key-value provider requires keyspace event notifications to be enabled for proper operation of the watch functionality. Enable this by running:

bash
$ redis-cli CONFIG SET notify-keyspace-events Kg$

Without this configuration, the watcher component won't receive notifications about key-value store operations. Note that this setting persists until explicitly changed or Redis is restarted.

Setting Watch Triggers​

You can set triggers for key-value operations using link configuration by adding a watch field with a comma-separated string of watch patterns. Each pattern follows the format OPERATION@key

bash
# wash config put <config-name> <values...>
wash config put custom-config foo=bar watch=SET@key,DEL@key

and load the custom-config while starting the provider

bash
# wash start provider <component_ref> <component_id> --config <config-name>
wash start provider ghcr.io/wasmcloud/keyvalue-redis:0.28.1 rust-keyvalue-watcher --config custom-config

You can also add the watch parameters under the link config properties inside the wadm manifest

yaml
# Under a link trait
config:
  - name: redis-custom
    properties:
        url: redis://0.0.0.0:6379
        watch: SET@key,DEL@key,.....

Note that only SET and DEL operations are supported in wasi:keyvalue@0.2.0-draft

Customizing Trigger Reactions​

The component currently sends HTTP requests to an alert server when watched operations occur. You can customize the reaction mechanism by modifying the on_set and on_delete functions in the KvWatcherDemoGuest implementation:

  • on_set: Triggered when the watched key undergoes a SET operation (Note: the value parameter contains the latest SET value of the Key.)s
rust
fn on_set(bucket: bindings::wasi::keyvalue::store::Bucket, key: String, value: Vec<u8>) {
    // Current implementation sends an HTTP request to localhost:3001/alert
    // You can modify this to implement different reactions
    // e.g., sending to different endpoints, formatting data differently,
    // or implementing entirely different reaction mechanisms
}
  • on_delete: Triggered when the watched key undergoes a DEL operation
rust
fn on_delete(bucket: bindings::wasi::keyvalue::store::Bucket, key: String) {
    // Current implementation sends an HTTP request to localhost:3001/alert
    // Customize this function to handle delete events differently
}

Examples of alternative reaction mechanisms you could implement:​

  • Send notifications to different services
  • Log to specific monitoring systems
  • Trigger cascading operations in other storage systems
  • Implement complex business logic based on the changes

Adding Capabilities​

To learn how to extend this example with additional capabilities, see the Adding Capabilities section of the wasmCloud documentation.