Subscribing to an AOI

[philvarner]

From @kbgg:

• Subscribing to an AoI radiantearth/stac-api-spec#6

It'd be nice to be able to be notified of any new items matching a specific search query. Currently the way to implement this would be to constantly poll the API and parse results to find an item which is new. Polling for updates would add unnecessary load to API servers when no new items exist. Ideally there would be a way for API consumers to subscribe to a search to only get updates when something is actually updated.

There's been talk about implementing this with webhooks, message brokers, or email.

For email I'm thinking of more user friendly emails which wouldn't be designed to be machine readable. In my QGIS plugin it'd be nice to have researchers subscribe to a study area and get an email whenever there's a new scene available for them to download.

First there should be an endpoint which list the subscription capabilities. By hitting this endpoint you can determine which subscription methods are supported by that server and how to subscribe to a topic. For example, if your server supports an SNS topic you might list the ARN for the collections.

Second there should be a way to subscribe to the topic for a specific subscription capability. If it's a webhook or email you would have an endpoint to register for that topic. If it's SNS it wouldn't be required since the ARN to subscribe is already listed in the capabilities portion.

Very rough ideas but I think it'd be a really good nice-to-have. This could also be used in the case of alerting users when an asset has been activated and is available for download.

Feedback is very much appreciated on this.

[philvarner]

Related:

• Subscribe to data changes? radiantearth/stac-api-spec#120