> ## 10 Releases

> This chapter should be read in conjuction with `rel(4)`, `systools(3)` and `script(4)`.

> ### 10.1 Release Concept

> When we have written one or more applications, we might want to create a complete system consisting of these applications and a subset of the Erlang/OTP applications. This is called a release.

> To do this, we create a release resource file which defines which applications are included in the release.

> The release resource file is used to generate boot scripts and release packages. A system which is transfered to and installed at another site is called a target system. How to use a release package to create a target system is described in System Principles.

> ### 10.2 Release Resource File

> To define a release, we create an release resource file, or in short `.rel` file:

>     {release, {Name,Vsn}, {erts, EVsn},
>      [{Application1, AppVsn1},
>        ...
>       {ApplicationN, AppVsnN}]}.

> The file must be named `Rel.rel`, where `Rel` is a unique name.

> `Name` and `Vsn` (strings) are the name and version of the release.

> `Evsn` (string) is the ERTS version the release is intended for.

> Each `Application` (atom) and `AppVsn` (string) is the name and version of an application included in the release. Note the the minimal release based on Erlang/OTP consists of the `kernel` and `stdlib` applications.

> Example: We want to make a release of `ch_app` from the Applications chapter. It has the following `.app` file:

>     {application, ch_app,
>      [{description, "Channel allocator"},
>       {vsn, "1"},
>       {modules, [ch_app, ch_sup, ch3]},
>       {registered, [ch3]},
>       {applications, [kernel, stdlib, sasl]},
>       {mod, {ch_app,[]}}
>      ]}.

> The release resource file must also contain `kernel`, `stdlib` and `sasl`, since these applications are required by `ch_app`. We call the file `ch_rel-1.rel`:

>     {release,
>      {"ch_rel", "1"},
>      {erts, "5.2.3.6"},
>      [{kernel, "2.8.1.3"},
>       {stdlib, "1.11.4.3"},
>       {sasl, "1.9.4"},
>       {ch_app, "1"}]
>     }.

> ### 10.3 Generating Boot Scripts

> There are tools in the module `systools` available to build and check releases. The functions read the release resource file and the application resource files and performs syntax and dependency checks. The function `systools:make_script/1,2` is used to generate a boot script.

>     1> systools:make_script("ch_rel-1", [local]).
>     ok

> This creates a boot script `ch_rel-1.script`. `"ch_rel-1"` is the name of the `.rel` file, minus the extension. `local` is an option that means that the directories where the applications are found are used in the boot script, instead of $ROOT/lib. ($ROOT is the root directory of the installed release.) This is a useful way to test a generated boot script locally.

> A binary version `ch_rel-1.boot` of the script must be generated:

>     2> systools:script2boot("ch_rel-1").
>     ok

> When starting Erlang/OTP using the boot script, all applications from the `.rel` file are automatically started:

>     % erl -boot ch_rel-1
>     Erlang (BEAM) emulator version 5.2.3.6 [hipe] [threads:0]

>     Eshell V5.2.3.6  (abort with ^G)
>     1>
>     =PROGRESS REPORT==== 13-Jun-2003::12:01:15 ===
>               supervisor: {local,sasl_safe_sup}
>                  started: [{pid,<0.33.0>},
>                            {name,alarm_handler},
>                            {mfa,{alarm_handler,start_link,[]}},
>                            {restart_type,permanent},
>                            {shutdown,2000},
>                            {child_type,worker}]

>     ...

>     =PROGRESS REPORT==== 13-Jun-2003::12:01:15 ===
>              application: sasl
>               started_at: nonode@nohost

>     ...
>     =PROGRESS REPORT==== 13-Jun-2003::12:01:15 ===
>              application: ch_app
>               started_at: nonode@nohost

> ### 10.4 Creating a Release Package

> There is a function `systools:make_tar/1,2` which takes a `.rel` file as input and creates a zipped tar-file with the code for the specified applications, a `release package`.

>     1> systools:make_script("ch_rel-1").
>     ok
>     2> systools:script2boot("ch_rel-1").
>     ok
>     3> systools:make_tar("ch_rel-1").
>     ok

> The release package by default contains the `.app` files and object code for all applications, structured according to the application directory structure, the binary boot script renamed to `start.boot`, and the release resource file.

>     % tar tf ch_rel-1.tar
>     lib/kernel-2.8.1.3/ebin/kernel.app
>     lib/kernel-2.8.1.3/ebin/application.beam
>     ...
>     lib/stdlib-1.11.4.3/ebin/stdlib.app
>     lib/stdlib-1.11.4.3/ebin/beam_lib.beam
>     ...
>     lib/sasl-1.9.4/ebin/sasl.app
>     lib/sasl-1.9.4/ebin/sasl.beam
>     ...
>     lib/ch_app-1/ebin/ch_app.app
>     lib/ch_app-1/ebin/ch_app.beam
>     lib/ch_app-1/ebin/ch_sup.beam
>     lib/ch_app-1/ebin/ch3.beam
>     releases/1/start.boot
>     releases/ch_rel-1.rel

> Options can be set to make the release package include source code and the ERTS binary as well.

> The release package should be unpacked and installed using the release handler. See System Principles for how this is done when installing a target system and Release Handling for how to do it in an existing system.

> ### 10.5 Directory Structure

> Directory structure for the code installed by the release handler from a release package:

>     $ROOTDIR/lib/App1-AVsn1/ebin
>                           /priv
>                 /App2-AVsn2/ebin
>                            /priv
>                 ...
>                 /AppN-AVsnN/ebin
>                            /priv
>             /erts-EVsn/bin
>             /releases/Vsn
>             /bin

> `lib`
>   Application directories.
> ``
>   The boot script and relup files should be located in the `releases/Vsn` directory. `Vsn` is the release version found in the release resource file.
> `erts-EVsn/bin`
>   Erlang runtime system executables.
> `releases/Vsn`
>   `.rel` file.
> `bin`
>   Top level Erlang executable program `erl`.

> Applications are not required to be located under the `$ROOTDIR/lib` directory. Accordingly, several installation directories may exist which contain different parts of a system. For example, the previous example could be extended as follows:

>     $SECOND_ROOT/.../SApp1-SAVsn1/ebin
>                                  /priv
>                     /SApp2-SAVsn2/ebin
>                                  /priv
>                     ...
>                     /SAppN-SAVsnN/ebin
>                                  /priv

>     $THIRD_ROOT/TApp1-TAVsn1/ebin
>                             /priv
>                /TApp2-TAVsn2/ebin
>                             /priv
>                ...
>                /TAppN-TAVsnN/ebin
>                             /priv

> The `$SECOND_ROOT` and `$THIRD_ROOT` are introduced as `variables` in the call to the `systools:make_script/2` function.

> #### 10.5.1 Disk-Less and/or Read-Only Clients

> If a complete system consists of some disk-less and/or read-only client nodes, a `clients` directory should be added to the `$ROOTDIR` directory. By a read-only node we mean a node with a read-only file system.

> The `clients` directory should have one sub-directory per supported client node. The name of each client directory should be the name of the corresponding client node. As a minimum, each client directory should contain the `bin` and `releases` sub-directories. These directories are used to store information about installed releases and to appoint the current release to the client. Accordingly, the `$ROOTDIR` directory contains the following:

>     $ROOTDIR/...
>             /clients/ClientName1/bin
>                                 /releases/Vsn
>                     /ClientName2/bin
>                                 /releases/Vsn
>                     ...
>                     /ClientNameN/bin
>                                 /releases/Vsn

> This structure should be used if all clients are running the same type of Erlang machine. If there are clients running different types of Erlang machines, or on different operating systems, the `clients` directory could be divided into one sub-directory per type of Erlang machine. Alternatively, you can set up one `ROOTDIR` per type of machine. For each type, some of the directories specified for the `ROOTDIR` directory should be included:

>     $ROOTDIR/...
>             /clients/Type1/lib
>                           /erts-EVsn
>                           /bin
>                           /ClientName1/bin
>                                       /releases/Vsn
>                           /ClientName2/bin
>                                       /releases/Vsn
>                           ...
>                           /ClientNameN/bin
>                                       /releases/Vsn
>                     ...
>                     /TypeN/lib
>                           /erts-EVsn
>                           /bin
>                           ...

> With this structure, the root directory for clients of `Type1` is `$ROOTDIR/clients/Type1`.

Copyright © 1991-2003 Ericsson Utvecklings AB