Overview

Overview

Relx is a tool that, given a specification, assembles releases. That is it makes an assessment of all of the Erlang/OTP Apps available to it and the constraints that you supply as part of your configuration and resolves a complete set of OTP Applications and their versions for use in the release. This may be a bit hard to understand if you are not familiar with the way version resolutions work in package management systems. So lets look at an example.

Lets say that you have the following OTP Applications

 app1-1.2
  with dependencies
    app2
    app5
    app6
app1-1.3
 with dependencies
   app2
   app6
app2-2.0
 with dependencies
   app6
app2-2.1
 with dependencies
   app6
   app7
app3-2.0
app4-1.0.0
app5-3.0
app6-1.0
 with dependencies
   app3
app7-2.0

This is the world of OTP Apps your Relx knows about (basically OTP Apps in the Library Directories you have specified). You have set a config that looks like the following:

 {release, {awesome_supercool, "1.0"},
    [{app1, "1.3", '>='},
     {app2, "2.0", '>'},
     app3]}

When the Relx process has run you will end up with a complete release as follows

{release, {awesome_supercool, "1.0"},
  [{app1, "1.3"},
   {app2, "2.1"},
   {app3, "2.0"},
   {app6, "1.0"},
   {app7, "2.0"}]}

As you can see that is a fully realized view of your direct and transitive dependencies based on the world that Relx knows about and the constraints that you specified in your configuration.

Next: Configuration