How to capture save or update events in Couchbase
Disclaimer: I work for Couchbase and develop the Java DCP client.
If you've already evaluated the Eventing service and decided it doesn't meet your requirements, the Java DCP client might be worth looking into even though it's not officially supported. It's used by the official Couchbase connectors for Kafka, Spark, and Elasticsearch (all of which are open source) and is actively maintained.
If you only care about events that happened since your app started up, usage can be as simple as registering a callback and starting the event stream. Things get a bit more complicated if you need to remember your place in the stream and resume later (to process events that occurred while you were offline, for example), but there's example code for that case too.
The DCP protocol itself is well documented. If you decide to go this route, it might be good to read at least the Architecture section of that documentation. Also be aware that because the Java DCP Client is unsupported, the API can change without notice. (Officially supporting the library and providing a friendlier API are among our long-term goals, but we haven't committed to anything yet.)
Like David, I also work for Couchbase as a product manager for the Eventing service.
I would like to be able to do some data manipulation when documents are updated or created in Couchbase.
Eventing certainly allows anyone to respond to and perform data manipulation on mutations (inserts or upserts) via tiny JavaScript fragments. Just take a look at couchbase-eventing-small-scripts-that-solve-big-problems for a quick introduction and also the eventing-examples from the documentation.
If you do go the Eventing service route on a SGW enabled bucket you will need to suppress a duplicate mutation via the crc64() function built into Eventing (for details goto eventing-language-constructs and search for: Sync Gateway). In addition if you want to have Eventing directly update the source bucket if SGW is enabled on that bucket there is a more involved workaround (just reach out to me and I will be happy to provide it)
Next you stated:
not sure I can run the Eventing service on our systems
The Eventing service bundled with the Couchbase Enterprise offering, it provides scalable infrastructure to run simple JavaScript fragments on data or documents as they change or mutate without the overhead of an SDK. You either add stand alone Eventing node(s) to your Couchbase cluster or collocate the Eventing service with other existing nodes.