The project uses rebar to manage dependencies with help of the rebar plugins.
When you just clone the repository of the project, you need to make get-deps
first to download all deps. Some make targets do it on their own though.
rebar.config.lock helps to create reproducible builds for the project.
It is generated by rebar-lock-deps plugin. The file lists every dependency
of the project and locks it at a specific git revision (see more info on
the plugin page).
When you change the deps section in any rebar.config file (the root one or of a dep),
you will need to update rebar.config.lock file. You can run
make update-lock to update the lock for all deps or
make update-lock apps=app1,app2 to update it for specific deps.
See also make update-lock.