10 Releases
This chapter should be read in conjuction with
rel(4)
,systools(3)
andscript(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
, whereRel
is a unique name.
Name
andVsn
(strings) are the name and version of the release.
Evsn
(string) is the ERTS version the release is intended for.Each
Application
(atom) andAppVsn
(string) is the name and version of an application included in the release. Note the the minimal release based on Erlang/OTP consists of thekernel
andstdlib
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
andsasl
, since these applications are required bych_app
. We call the filech_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 functionsystools:make_script/1,2
is used to generate a boot script.1> systools:make_script("ch_rel-1", [local]). okThis 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"). okWhen 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@nohost10.4 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, arelease package
.1> systools:make_script("ch_rel-1"). ok 2> systools:script2boot("ch_rel-1"). ok 3> systools:make_tar("ch_rel-1"). okThe 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 tostart.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.relOptions 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 /privThe
$SECOND_ROOT
and$THIRD_ROOT
are introduced asvariables
in the call to thesystools: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$ROOTDIR
directory. By a read-only node we mean a node with a read-only file system.The
clients
directory should have one sub-directory per supported client node. The name of each client directory should be the name of the corresponding client node. As a minimum, each client directory should contain thebin
andreleases
sub-directories. These directories are used to store information about installed releases and to appoint the current release to the client. Accordingly, the$ROOTDIR
directory contains the following:$ROOTDIR/... /clients/ClientName1/bin /releases/Vsn /ClientName2/bin /releases/Vsn ... /ClientNameN/bin /releases/VsnThis structure should be used if all clients are running the same type of Erlang machine. If there are clients running different types of Erlang machines, or on different operating systems, the
clients
directory could be divided into one sub-directory per type of Erlang machine. Alternatively, you can set up oneROOTDIR
per type of machine. For each type, some of the directories specified for theROOTDIR
directory should be included:$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
.