With the release of OTP-21 and rebar3 3.6.0, which includes a new relx 3.25.0, there is better support for dynamic configuration of releases at runtime. If you are new to this concept checkout the rebar3 docs first
No longer will you be forced to declare RELX_REPLACE_OS_VARS and convert strings to integers in your code because the sys.config file had to be valid Erlang terms when building the release.
Instead, you can use {sys_config_src, "config/sys. ...