[[relx]]
== Releases

Erlang.mk relies on _Relx_ for generating releases. This
chapter covers the Erlang.mk-specific bits. Consult the
https://erlware.github.io/relx/[Relx website] for more information.

=== Setup

Erlang.mk will create a release if it detects a Relx configuration
file in the '$(RELX_CONFIG)' location. This defaults to
'$(CURDIR)/relx.config'. You can override it by defining
the variable before including Erlang.mk:

[source,make]
RELX_CONFIG = $(CURDIR)/webchat.config

Relx does not need to be installed. Erlang.mk will download
and build it automatically.

The Relx executable will be saved in the '$(RELX)' file. This
location defaults to '$(CURDIR)/relx' and can be overriden.

// @todo You can use a custom location by ???

=== Configuration

You can specify additional Relx options using the `RELX_OPTS`
variable. For example, to enable `dev_mode`:

[source,make]
RELX_OPTS = -d true

While you can specify the output directory for the release
in the Relx options directly, Erlang.mk provides a specific
variable for it: `RELX_OUTPUT_DIR`. It defaults to the '_rel'
directory. You can also override it:

[source,make]
RELX_OUTPUT_DIR = /path/to/staging/directory

=== Generating the release

Now that you're all set, all you need to do is generate the
release. As mentioned before, Erlang.mk will automatically
generate it when it detects the '$(RELX_CONFIG)' file. This
means the following command will also build the release:

[source,bash]
$ make

If you need to generate the release, and only the release,
the `rel` target can be used:

[source,bash]
$ make rel

Erlang.mk always generates a tarball alongside the release,
which can be directly uploaded to a server. The tarball is
located at `$(RELX_OUTPUT_DIR)/<name>/<name>-<vsn>.tar.gz`.

=== Running the release

Erlang.mk provides a convenience function for running the
release with one simple command:

[source,bash]
$ make run

This command will also build the project and generate the
release if they weren't already. It starts the release in
_console mode_, meaning you will also have a shell ready to
use to check things as needed.

=== Upgrading a release

Erlang.mk provides a `relup` target for generating release
upgrades. Release upgrades allow updating the code and the
state of a running release without restarting it.

Once your changes are done, you need to update the version
of the application(s) that will be updated. You also need
to update the version of the release.

For each application that needs to be updated, an
http://erlang.org/doc/man/appup.html[appup file]
must be written. Refer to the Erlang/OTP documentation
for more details.

For the purpose of this section, assume the initial release
version was `1`, and the new version is `2`. The name of the
release will be `example`.

Once all this is done, you can build the tarball for the
release upgrade:

[source,bash]
$ make relup

This will create an archive at the root directory of the
release, `$(RELX_OUTPUT_DIR)/example/example-2.tar.gz`.

Move the archive to the correct location on the running
node. From the release's root directory:

[source,bash]
$ mkdir releases/2/
$ mv path/to/example-2.tar.gz releases/2/

Finally, upgrade the release:

[source,bash]
$ bin/example_release upgrade "2/example_release"

Or on Windows:

[source,bash]
$ bin/example_release.cmd upgrade "2/example_release"

Your release was upgraded!
