add Erlang/OTP example

examples/erlang/README.md

@@ -0,0 +1,228 @@
+You need to have [`Erlang/OTP`](http://erlang.org), [`Rebar3`](http://rebar3.org) (Erlang build tool) and `warp-packer` installed to create self-contained binary Erlang release.
+
+## Linux
+Create new application using `rebar3`: 
+```sh
+~ $ rebar3 new app foo && cd foo
+```
+```txt
+===> Writing foo/src/foo_app.erl
+===> Writing foo/src/foo_sup.erl
+===> Writing foo/src/foo.app.src
+===> Writing foo/rebar.config
+===> Writing foo/.gitignore
+===> Writing foo/LICENSE
+===> Writing foo/README.md
+```
+```sh
+~/foo $ 
+```
+
+Make a directory (e.g. `config`) to place `warp` launcher in it:  
+```sh
+~/foo $ mkdir config
+```
+Create `./config/launch` file with below contents:
+```sh
+#!/bin/sh
+
+DIR="$(cd "$(dirname "$0")" ; pwd -P)"
+APP=$DIR/bin/{{release_name}}
+
+exec $APP $@
+```
+We used [`mustache`](https://mustache.github.io/) template to let `rebar3` place your release name in script dynamically. Here it is `foo`. 
+
+Make launcher file executable:
+```sh
+~/foo $ chmod a+x config/launch
+```
+
+Edit `rebar.config` file and add `relx` section:
+```erlang
+% ...
+
+{relx, [{release, { foo, "0.1.0" }, [foo, sasl]},
+
+        {dev_mode, false},
+        {include_erts, true}, % To include Erlang runtime system
+        {extended_start_script, true}, % Should be true
+
+        {overlay, [{template, "./config/launch", "launch"}]}] % copies our launcher file to release directory
+}.
+
+% ...
+```
+
+Make a release:
+```sh
+~/foo $ rebar3 release
+```
+```text
+===> Verifying dependencies...
+===> Compiling foo
+===> Starting relx build process ...
+===> Resolving OTP Applications from directories:
+          /opt/foo/_build/default/lib
+          /usr/local/lib/erlang/lib
+          /opt/foo/_build/default/rel
+===> Resolved foo-0.1.0
+===> Including Erts from /usr/local/lib/erlang
+===> release successfully created!
+```
+Now launcher file should be in your release directory:
+```sh
+~/foo $ ls _build/default/rel/foo 
+bin  erts-10.1  launch  lib  releases
+```
+
+Before running `warp-packer`, It's better to test release itself:
+```sh
+~/foo $ ./_build/default/rel/foo/bin/foo start
+~/foo $ ./_build/default/rel/foo/bin/foo ping
+pong
+~/foo $ ./_build/default/rel/foo/bin/foo stop
+ok
+```
+
+Build self-contained binary file from release:
+```sh
+~/foo $ warp-packer -a linux-x64 -i _build/default/rel/foo -e launch -o foo
+```
+```text
+Compressing input directory "_build/default/rel/foo"...
+Creating self-contained application binary "foo"...
+All done
+```
+
+Test it:
+```sh
+~/foo $ ./foo start
+```
+```sh
+~/foo $ ./foo ping
+pong
+```
+```sh
+~/foo $ ./foo remote_console
+Erlang/OTP 21 [erts-10.1] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]
+
+Eshell V10.1  (abort with ^G)
+(foo@localhost)1>
+BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
+       (v)ersion (k)ill (D)b-tables (d)istribution
+```
+```sh
+~/foo $ ./foo stop
+ok
+```
+```sh
+~/foo $ ./foo ping
+Node foo@localhost not responding to pings.
+```
+
+#### Advanced
+You can place `warp` command in `rebar.config`. Then `rebar3` will run it when you are making release:
+```erlang
+% ...
+
+{post_hooks, [{release, "warp-packer -a linux-x64 -i _build/default/rel/foo -e launch -o foo"}]}.
+
+% ...
+```
+Now make release:
+```sh
+~/foo $ rebar3 release
+```
+```text
+===> Verifying dependencies...
+===> Compiling foo
+===> Starting relx build process ...
+===> Resolving OTP Applications from directories:
+          /opt/foo/_build/default/lib
+          /usr/local/lib/erlang/lib
+          /opt/foo/_build/default/rel
+===> Resolved foo-0.1.0
+===> Including Erts from /usr/local/lib/erlang
+===> release successfully created!
+Compressing input directory "_build/default/rel/foo"...
+Creating self-contained application binary "foo"...
+All done
+```
+
+Note that `rebar3` uses a templating approach to make an application structure. If you built `rebar3`by yourself, and did not use its escript, Its own templates are placed in `/path/to/installed/rebar3/priv/templates`.
+You can place your `launch` file there and add below lines at the end of `app.template`:
+```erlang
+% ...
+{file, "launch", "{{name}}/config/launch"}. % copies launch file to YourApp/config/launch
+{chmod, "{{name}}/config/launch", 8#755}. % makes file executable
+```
+Also edit `app_rebar.config` and place our `relx` and `post_hooks` at the end of file:
+```erlang
+% ...
+
+{relx, [{release, { {{name}}, "0.1.0" },
+         [{{name}}, sasl]},
+
+        {dev_mode, false},
+        {include_erts, true},
+
+        {extended_start_script, true},
+        {overlay, [{template, "./config/launch", "launch"}]}]
+}.
+
+{post_hooks, [{release, "warp-packer -a linux-x64 -i _build/default/rel/{{name}} -e launch -o {{name}}"}]}.
+```
+In above `{{name}}` is what you will pass to `rebar3 new app` as application name. Recompile `rebar3` itself again: 
+```sh
+/path/to/rebar3 $ ./bootsrtap
+...
+```
+
+Create new application again:
+```sh
+~ $ rebar3 new app bar && cd bar
+```
+```text
+===> Writing bar/src/bar_app.erl
+===> Writing bar/src/bar_sup.erl
+===> Writing bar/src/bar.app.src
+===> Writing bar/rebar.config
+===> Writing bar/.gitignore
+===> Writing bar/LICENSE
+===> Writing bar/README.md
+===> Writing bar/config/launch
+```
+Make a release:
+```sh
+~/bar $ rebar3 release
+```
+```text
+===> Verifying dependencies...
+===> Compiling bar
+===> Starting relx build process ...
+===> Resolving OTP Applications from directories:
+          /opt/bar/_build/default/lib
+          /usr/local/lib/erlang/lib
+===> Resolved bar-0.1.0
+===> Including Erts from /usr/local/lib/erlang
+===> release successfully created!
+Compressing input directory "_build/default/rel/bar"...
+Creating self-contained application binary "bar"...
+All done
+```
+
+Test it:
+```sh
+~/bar $ ./bar start
+```
+```sh
+~/bar $ ./bar ping
+pong
+```
+```sh
+~/bar $ ./bar stop
+ok
+```
+
+Also you can add it for `rebar3 new release | lib` or [build your own template](https://www.rebar3.org/docs/using-templates#section-custom-templates) and add it to your template.