How to sell a server application?

Question

Node.js

Hello. I was interested in such a question, I haven’t googled it much yet, but it’s interesting to know the experience of other developers, if any.
Let's say there is some kind of server application that it is desirable to install locally on the server. And there are customers from whom you need to charge for the use of this application.
1) How to license an application programmatically?
2) How to check if a customer has subscribed to a product?
3) How to protect the application from copying and modifying?

Answer 1

Let's say there is some kind of server application that it is desirable to install locally on the server.

The short answer is no, but there is an option.
Why?
1. Few people will install unknown things on the server and pay money for it.
2. Any functionality written by one developer can be easily copied by any other developers by developing the same functionality from scratch.
3. If your application has calculations and work with data, then it is better to do it as a SaaS service .
4. If the data needs to be processed only at the application client (in its server room) in local mode, then create a micro data processing module (in which the formulas and algorithms necessary for processing are "hardwired") with access to it by key through the local API ( IMPORTANT: the module itself never goes online!) received through your SaaS service, and which will be renewed / updated through the same SaaS service (this is exactly the option ...).

Answer 2

Everything is standard. First, protect yourself with a license. Yes, these are the people who are lawyers :)
The second is to embed a check in the update module.
Your third application should be something like 1c, guarantor or antivirus. That is, disconnecting from updates makes him a pumpkin