I was looking into ejabberd and found it is licensed under GPLv2. Let’s say that I am using it as follows:
You will come to my website/app and login, then start a chat using Instant messanger. I will use ejabbered on server side to handle and process your messaging and chating. Do I have to make my application code open source ?
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No, you don’t need to open source your application.
You only need to open source a work derived from a GPL work when you distribute the work. But when your program runs your own server, you are not distributing it to your users. That means you do not need to license it to them. You can even modify the sourcecode. As long as the software doesn’t leave your server, the sourcecode doesn’t have to leave it either.
There is the AGPL which closes this loophole by requiring to sublicense the work to everyone who interacts with the software via a computer network, but the normal GPLv2 does not include this clause.
One thing web developers need to be aware of when they use GPL software is that the situation is different when you use GPL-licensed JavaScript, HTML or CSS code. When GPL-derived code is sent to and executed by the client, that code must also be licensed under GPL. But this is only a problem when you use GPL-licensed javascript. It is not a problem when your own JavaScript code is interacting with a GPL-licensed backend.
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