Awesome

The setup application

Authors: Ulf Wiger (ulf@wiger.net).

Generic setup utility for Erlang-based systems

Introduction

While Erlang/OTP comes with many wonderful applications, including the Mnesia DBMS, there is no standard or convention for installing a system. Erlang/OTP provides tools for building a boot script, and rules for setting environment variables, etc., and Mnesia offers an API for creating and modifying the database schema.

However, with no convention for when these tools and API functions are called - and by whom - application developers are left having to invent a lot of code and scripts, not to mention meditate over chapters of Erlang/OTP documentation in order to figure out how things fit together.

This utility offers a framework for initializing and configuring a system, with a set of conventions allowing each component to provide callbacks for different steps in the installation procedure.

The callbacks are defined through OTP application environment variables, which can easily be overridden at install time.

The setup_gen utility

The setup_gen utility is a simple tool to generate .rel file and boot script for an Erlang-based system. It fetches configuration options from a .conf file (read using file:script/2). As an example of a very simple build, see examples/gproc.conf':

[{apps, [kernel,
	 stdlib,
	 sasl,
	 gproc]}].

This configuration file simply lists the applications to start from the boot script. The setup_gen script can either be called from within Erlang as:

Eshell V5.8.1  (abort with ^G)
1> setup_gen:run([{conf,"gproc.conf"},{outdir,"."},{name,"gproc"}]).
Options = [{conf,"gproc.conf"},{outdir,"."},{name,"gproc"}]
Paths = []
add path Res = ok
app_vsn(kernel) -> "2.14.1"
app_vsn(stdlib) -> "1.17.1"
app_vsn(sasl) -> "2.1.9.2"
app_vsn(gproc) -> "0.01"
Rel: {release,{"gproc","tmp"},
              {erts,"5.8.1"},
              [{kernel,"2.14.1"},
               {stdlib,"1.17.1"},
               {sasl,"2.1.9.2"},
               {gproc,"0.01"}]}
entering directory .
Path = []
make_script() -> ok
ok

...or as an escript:

escript ~/git/setup/ebin/setup_gen.beam gproc gproc.conf .

If the option -install true is given, the setup_gen utility will generate an installation boot script, and install.config file, which can be used to install the system, using a command like:

erl -sys install -boot install

This boot script will run kernel, stdlib and sasl, then load all other applications, and finally run the setup application, which will find and execute any setup hooks.

If the option -setup stop_when_done true is added to the command line, the setup application will automatically shut down all running nodes after running the setup hooks. Otherwise (default), it will hand over control to the shell rather than terminate the Erlang VM.

See setup_gen:run/1 for documentation on all supported options.

Variable expansion

setup extends the functionality of application:get_env/[2,3] by also supporting variable expansion, as well as a function for searching all applications for instances of a given variable. This functionality is described in setup.

Modules