What's APGL? Anti Personnel Grenade Launchers?
You only have to provide the source of derivative work, and only to users of your service.
So only the micro service using AGPL code.
If you use an AGPL database for example, you don't have to provide any source code unless you change the source code of the database. This idea was behind the business models of Rethink DB and Mongo DB.
A microservice doesn't get around it if it's tightly coupled. It would only be enough if your main application was not dependent on the AGPL microservice (e.g. you have another image processing microservice that provides perfect parity).
I guess it's AGPL then.