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<!DOCTYPE chapter SYSTEM "chapter.dtd">

<chapter>
  <header>
    <copyright>
      <year>2003</year><year>2011</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.
    
      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.
    
    </legalnotice>

    <title>Releases</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>release_structure.xml</file>
  </header>
  <p>This chapter should be read in conjuction with <c>rel(4)</c>,
    <c>systools(3)</c> and <c>script(4)</c>.</p>

  <section>
    <title>Release Concept</title>
    <p>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
      <em>release</em>.</p>
    <p>To do this, we create a <seealso marker="#res_file">release resource file</seealso> which defines which applications
      are included in the release.</p>
    <p>The release resource file is used to generate
      <seealso marker="#boot">boot scripts</seealso> and
      <seealso marker="#pack">release packages</seealso>. A system
      which is transfered to and installed at another site is called a
      <em>target system</em>. How to use a release package to create a
      target system is described in System Principles.</p>
  </section>

  <section>
    <marker id="res_file"></marker>
    <title>Release Resource File</title>
    <p>To define a release, we create a <em>release resource file</em>,
      or in short <c>.rel</c> file, where we specify the name and
      version of the release, which ERTS version it is based on, and
      which applications it consists of:</p>
    <code type="none">
{release, {Name,Vsn}, {erts, EVsn},
 [{Application1, AppVsn1},
   ...
  {ApplicationN, AppVsnN}]}.</code>
    <p>The file must be named <c>Rel.rel</c>, where <c>Rel</c> is a
      unique name.</p>
    <p><c>Name</c>, <c>Vsn</c> and <c>EVsn</c> are strings.</p>
    <p>Each <c>Application</c> (atom) and <c>AppVsn</c> (string) is
      the name and version of an application included in the release.
      Note that the minimal release based on Erlang/OTP consists of
      the <c>kernel</c> and <c>stdlib</c> applications, so these
      applications must be included in the list.</p>
    <p>If the release is to be upgraded, it must also include
      the <c>sasl</c> application.</p>
    <marker id="ch_rel"></marker>
    <p>Example: We want to make a release of <c>ch_app</c> from
      the <seealso marker="applications#ch_app">Applications</seealso>
      chapter. It has the following <c>.app</c> file:</p>
    <code type="none">
{application, ch_app,
 [{description, "Channel allocator"},
  {vsn, "1"},
  {modules, [ch_app, ch_sup, ch3]},
  {registered, [ch3]},
  {applications, [kernel, stdlib, sasl]},
  {mod, {ch_app,[]}}
 ]}.</code>
    <p>The <c>.rel</c> file must also contain <c>kernel</c>,
      <c>stdlib</c> and <c>sasl</c>, since these applications are
      required by <c>ch_app</c>. We call the file <c>ch_rel-1.rel</c>:</p>
    <code type="none">
{release,
 {"ch_rel", "A"},
 {erts, "5.3"},
 [{kernel, "2.9"},
  {stdlib, "1.12"},
  {sasl, "1.10"},
  {ch_app, "1"}]
}.</code>
  </section>

  <section>
    <marker id="boot"></marker>
    <title>Generating Boot Scripts</title>
    <p>There are tools in the SASL module <c>systools</c> available to
      build and check releases. The functions read the <c>.rel</c> and
      <c>.app</c> files and performs syntax and dependency checks.
      The function <c>systools:make_script/1,2</c> is used to generate
      a boot script (see System Principles).</p>
    <pre>
1> <input>systools:make_script("ch_rel-1", [local]).</input>
ok</pre>
    <p>This creates a boot script, both the readable version
      <c>ch_rel-1.script</c> and the binary version used by the runtime
      system, <c>ch_rel-1.boot</c>. <c>"ch_rel-1"</c> is the name of
      the <c>.rel</c> file, minus the extension. <c>local</c> is an
      option that means that the directories where the applications are
      found are used in the boot script, instead of <c>$ROOT/lib</c>.
      (<c>$ROOT</c> is the root directory of the installed release.)
      This is a useful way to test a generated boot script locally.</p>
    <p>When starting Erlang/OTP using the boot script, all applications
      from the <c>.rel</c> file are automatically loaded and started:</p>
    <pre>
% <input>erl -boot ch_rel-1</input>
Erlang (BEAM) emulator version 5.3

Eshell V5.3  (abort with ^G)
1> 
=PROGRESS REPORT==== 13-Jun-2003::12:01:15 ===
          supervisor: {local,sasl_safe_sup}
             started: [{pid,&lt;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</pre>
  </section>

  <section>
    <marker id="pack"></marker>
    <title>Creating a Release Package</title>
    <p>There is a function <c>systools:make_tar/1,2</c> which takes
      a <c>.rel</c> file as input and creates a zipped tar-file with
      the code for the specified applications, a <em>release package</em>.</p>
    <pre>
1> <input>systools:make_script("ch_rel-1").</input>
ok
2> <input>systools:make_tar("ch_rel-1").</input>
ok</pre>
    <p>The release package by default contains the <c>.app</c> files and
      object code for all applications, structured according to
      the <seealso marker="applications#app_dir">application directory structure</seealso>, the binary boot script renamed to
      <c>start.boot</c>, and the <c>.rel</c> file.</p>
    <pre>
% <input>tar tf ch_rel-1.tar</input>
lib/kernel-2.9/ebin/kernel.app
lib/kernel-2.9/ebin/application.beam
...
lib/stdlib-1.12/ebin/stdlib.app
lib/stdlib-1.12/ebin/beam_lib.beam
...
lib/sasl-1.10/ebin/sasl.app
lib/sasl-1.10/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/A/start.boot
releases/A/ch_rel-1.rel
releases/ch_rel-1.rel</pre>
    <p>Note that a new boot script was generated, without
      the <c>local</c> option set, before the release package was made.
      In the release package, all application directories are placed
      under <c>lib</c>. Also, we do not know where the release package
      will be installed, so we do not want any hardcoded absolute paths
      in the boot script here.</p>
    <p>The release resource file <c>mysystem.rel</c> is duplicated in
      the tar file. Originally, this file was only stored in
      the <c>releases</c> directory in order to make it possible for
      the <c>release_handler</c> to extract this file
      separately. After unpacking the tar file, <c>release_handler</c>
      would automatically copy the file
      to <c>releases/FIRST</c>. However, sometimes the tar file is
      unpacked without involving the <c>release_handler</c> (e.g. when
      unpacking the first target system) and therefore the file is now
      instead duplicated in the tar file so no manual copying is
      necessary.</p>
    <p>If a <c>relup</c> file and/or a system configuration file called
      <c>sys.config</c> is found, these files are included in
      the release package as well. See
      <seealso marker="release_handling#req">Release Handling</seealso>.</p>
    <p>Options can be set to make the release package include source
      code and the ERTS binary as well.</p>
    <p>Refer to System Principles for how to install the first target
      system, using a release package, and to
      <seealso marker="release_handling">Release Handling</seealso> for
      how to install a new release package in an existing system.</p>
  </section>

  <section>
    <marker id="reldir"></marker>
    <title>Directory Structure</title>
    <p>Directory structure for the code installed by the release handler
      from a release package:</p>
    <code type="none">
$ROOT/lib/App1-AVsn1/ebin
                    /priv
         /App2-AVsn2/ebin
                    /priv
         ...
         /AppN-AVsnN/ebin
                    /priv
     /erts-EVsn/bin
     /releases/Vsn
     /bin</code>
    <taglist>
      <tag><c>lib</c></tag>
      <item>Application directories.</item>
      <tag><c>erts-EVsn/bin</c></tag>
      <item>Erlang runtime system executables.</item>
      <tag><c>releases/Vsn</c></tag>
      <item><c>.rel</c> file and boot script <c>start.boot</c>.      <br></br>

       If present in the release package,      <br></br>
<c>relup</c> and/or <c>sys.config</c>.</item>
      <tag><c>bin</c></tag>
      <item>Top level Erlang runtime system executables.</item>
    </taglist>
    <p>Applications are not required to be located under the
      <c>$ROOT/lib</c> directory. Accordingly, several installation
      directories may exist which contain different parts of a
      system. For example, the previous example could be extended as
      follows:</p>
    <pre>
$SECOND_ROOT/.../SApp1-SAVsn1/ebin
                             /priv
                /SApp2-SAVsn2/ebin
                             /priv
                ...
                /SAppN-SAVsnN/ebin
                             /priv

$THIRD_ROOT/TApp1-TAVsn1/ebin
                        /priv
           /TApp2-TAVsn2/ebin
                        /priv
           ...
           /TAppN-TAVsnN/ebin
                        /priv</pre>
    <p>The <c>$SECOND_ROOT</c> and <c>$THIRD_ROOT</c> are introduced as
      <c>variables</c> in the call to the <c>systools:make_script/2</c>
      function.</p>

    <section>
      <title>Disk-Less and/or Read-Only Clients</title>
      <p>If a complete system consists of some disk-less and/or
        read-only client nodes, a <c>clients</c> directory should be
        added to the <c>$ROOT</c> directory. By a read-only node we
        mean a node with a read-only file system.</p>
      <p>The <c>clients</c> directory should have one sub-directory
        per supported client node. The name of each client directory
        should be the name of the corresponding client node. As a
        minimum, each client directory should contain the <c>bin</c> and
        <c>releases</c> sub-directories. These directories are used to
        store information about installed releases and to appoint the
        current release to the client. Accordingly, the <c>$ROOT</c>
        directory contains the following:</p>
      <code type="none">
$ROOT/...
    /clients/ClientName1/bin
                        /releases/Vsn
            /ClientName2/bin
                        /releases/Vsn
            ...
            /ClientNameN/bin
                        /releases/Vsn</code>
      <p>This structure should be used if all clients are running
        the same type of Erlang machine. If there are clients running
        different types of Erlang machines, or on different operating
        systems, the <c>clients</c> directory could be divided into one
        sub-directory per type of Erlang machine. Alternatively, you
        can set up one <c>$ROOT</c> per type of machine. For each
        type, some of the directories specified for the <c>$ROOT</c>
        directory should be included:</p>
      <code type="none">
$ROOT/...
    /clients/Type1/lib
                  /erts-EVsn
                  /bin
                  /ClientName1/bin
                              /releases/Vsn
                  /ClientName2/bin
                              /releases/Vsn
                  ...
                  /ClientNameN/bin
                              /releases/Vsn
            ...
            /TypeN/lib
                  /erts-EVsn
                  /bin
                  ...</code>
      <p>With this structure, the root directory for clients of
        <c>Type1</c> is <c>$ROOT/clients/Type1</c>.</p>
    </section>
  </section>
</chapter>

