I am creating small app running multiple microservices. I would like to have this app available 24/7, so free dyno hours are not enough for me. If I upgrade to a hobby plan I would get 10 Process Types.
Can I run another microservice on each of the processes (web), or does Heroku give me the ability only to install one web process per dyno, and the other 10 process types are for scaling my app? In other words, If i need 6 microservices running 24/7 should I buy 6 hobby dynos?
You can only have 1 web process type. You can horizontally scale your web process to run on multiple dynos ("horizontal scalability"), however you will need to upgrade to at least standard-1x dyno types to do that (i.e. you can only run 1 web dyno instance if you are using free or hobby dyno types).
However, in addition to your web process, you can instantiate multiple additional process types (e.g. "worker" processes). These will NOT be able to listen on HTTP/S requests from your clients, but can be used for offloading long-running jobs from your web process.
So, if you map each of your 4-6 microservices to a different Process Type in your Procfile, and if your microservices are not themselves web servers, you might be able to make do with hobby dynos.