release_handler
Unpacking and Installation of Release Packages
The release handler is a process belonging to the SASL application which is responsible for release handling, that is, unpacking, installation, and removal of release packages.
An introduction to release handling and a usage example can be found in Design Principles.
A release package is a compressed tar file containing
code for a certain version of a release, created by calling
systools:make_tar/1,2.
The release package should be placed in the $ROOT/releases
directory of the previous version of the release where
$ROOT
is the installation root directory,
code:root_dir()
.
Another releases
directory can be specified using the SASL
configuration parameter releases_dir
, or the OS environment
variable RELDIR
. The release handler must have write access
to this directory in order to install the new release.
The persistent state of the release handler is stored there in a
file called RELEASES
.
A release package should always contain the release resource file
Name.rel
and a boot script Name.boot
. It may contain
a release upgrade file relup
and a system configuration
file sys.config
. The .rel
file contains information
about the release: its name, version, and which ERTS and
application versions it uses. The relup
file contains
scripts for how to upgrade to, or downgrade from, this version of
the release.
The release package can be unpacked, which extracts
the files. An unpacked release can be installed.
The currently used version of the release is then upgraded or
downgraded to the specified version by evaluating the instructions
in relup
. An installed release can be made
permanent. There can only be one permanent release in
the system, and this is the release that is used if the system is
restarted. An installed release, except the permanent one, can be
removed. When a release is removed, all files that
belong to that release only are deleted.
Each version of the release has a status. The status can be
unpacked
, current
, permanent
, or old
.
There is always one latest release which either has status
permanent
(normal case), or current
(installed, but
not yet made permanent). The following table illustrates
the meaning of the status values:
Status Action NextStatus ------------------------------------------- - unpack unpacked unpacked install current remove - current make_permanent permanent install other old remove - permanent make other permanent old install permanent old reboot_old permanent install current remove -
The release handler process is a locally registered process on each node. When a release is installed in a distributed system, the release handler on each node must be called. The release installation may be synchronized between nodes. From an operator view, it may be unsatisfactory to specify each node. The aim is to install one release package in the system, no matter how many nodes there are. If this is the case, it is recommended that software management functions are written which take care of this problem. Such a function may have knowledge of the system architecture, so it can contact each individual release handler to install the package.
For release handling to work properly, the runtime system needs
to have knowledge about which release it is currently running. It
must also be able to change (in run-time) which boot script and
system configuration file should be used if the system is
restarted. This is taken care of automatically if Erlang is
started as an embedded system. Read about this in Embedded System. In this case, the system configuration file
sys.config
is mandatory.
A new release may restart the system. Which program to use is
specified by the SASL configuration parameter start_prg
which defaults to $ROOT/bin/start
.
The emulator restart on Windows NT expects that the system is
started using the erlsrv
program (as a service).
Furthermore the release handler expects that the service is named
NodeName_Release, where NodeName is
the first part of the Erlang nodename (up to, but not including
the "@") and Release is the current release of
the application. The release handler furthermore expects that a
program like start_erl.exe
is specified as "machine" to
erlsrv
. During upgrading with restart, a new service will
be registered and started. The new service will be set to
automatic and the old service removed as soon as the new release
is made permanent.
The release handler at a node which runs on a diskless machine,
or with a read-only file system, must be configured accordingly
using the following sasl
configuration parameters (see
sasl(6) for details):
masters
-
This node uses a number of master nodes in order to store and fetch release information. All master nodes must be up and running whenever release information is written by this node.
client_directory
-
The
client_directory
in the directory structure of the master nodes must be specified. static_emulator
-
This parameter specifies if the Erlang emulator is statically installed at the client node. A node with a static emulator cannot dynamically switch to a new emulator because the executable files are statically written into memory.
It is also possible to use the release handler to unpack and install release packages when not running Erlang as an embedded system, but in this case the user must somehow make sure that correct boot scripts and configuration files are used if the system needs to be restarted.
There are additional functions for using another file structure than the structure defined in OTP. These functions can be used to test a release upgrade locally.
Functions
check_install_release(Vsn) -> {ok, OtherVsn, Descr} | {error, Reason}
Vsn = OtherVsn = string()
Descr = term()
Reason = term()
Checks if the specified version Vsn
of the release
can be installed. The release must not have status
current
. Issues warnings if relup
or
sys.config
are not present. If relup
is present,
its contents are checked and {error,Reason}
is
returned if an error is found. Also checks that all required
applications are present and that all new code can be loaded,
or {error,Reason}
is returned.
This function evaluates all instructions that occur before
the point_of_no_return
instruction in the release
upgrade script.
Returns the same as install_release/1
. Descr
defaults to "" if no relup
file is found.
create_RELEASES(Root, RelDir, RelFile, AppDirs) -> ok | {error, Reason}
Root = RelDir = RelFile = string()
AppDirs = [{App, Vsn, Dir}]
App = atom()
Vsn = Dir = string()
Reason = term()
Creates an initial RELEASES file to be used by the release handler. This file must exist in order to install new releases.
Root
is the root of the installation ($ROOT
) as
described above. RelDir
is the the directory where
the RELEASES
file should be created (normally
$ROOT/releases
). RelFile
is the name
of the .rel
file that describes the initial release,
including the extension .rel
.
AppDirs
can be used to specify from where the modules
for the specified applications should be loaded. App
is
the name of an application, Vsn
is the version, and
Dir
is the name of the directory where App-Vsn
is located. The corresponding modules should be located under
Dir/App-Vsn/ebin
. The directories for applications not
specified in AppDirs
are assumed to be located in
$ROOT/lib
.
install_file(Vsn, File) -> ok | {error, Reason}
Vsn = File = string()
Reason = term()
Installs a release dependent file in the release structure.
A release dependent file is a file that must be in
the release structure when a new release is installed:
start.boot
, relup
and sys.config
.
The function can be called, for example, when these files
are generated at the target. It should be called after
set_unpacked/2
has been called.
install_release(Vsn) -> {ok, OtherVsn, Descr} | {error, Reason}
install_release(Vsn, [Opt]) -> {ok, OtherVsn, Descr} | {error, Reason}
Vsn = OtherVsn = string()
Opt = {error_action, Action} | {code_change_timeout, Timeout}
| {suspend_timeout, Timeout} | {update_paths, Bool}
Action = restart | reboot
Timeout = default | infinity | int()>0
Bool = boolean()
Descr = term()
Reason = {illegal_option, Opt} | {already_installed, Vsn} | {change_appl_data, term()} | term()
Installs the specified version Vsn
of the release.
Looks first for a relup
file for Vsn
and a
script {UpFromVsn,Descr1,Instructions1}
in this file
for upgrading from the current version. If not found,
the function looks for a relup
file for the current
version and a script {Vsn,Descr2,Instructions2}
in this
file for downgrading to Vsn
.
If a script is found, the first thing that happens is that
the applications specifications are updated according to
the .app
files and sys.config
belonging to
the release version Vsn
.
After the application specifications have been updated,
the instructions in the script are evaluated and the function
returns {ok,OtherVsn,Descr}
if successful.
OtherVsn
and Descr
are the version
(UpFromVsn
or Vsn
) and description
(Descr1
or Descr2
) as specified in the script.
If a recoverable error occurs, the function returns
{error,Reason}
and the original application
specifications are restored. If a non-recoverable error
occurs, the system is restarted.
The option error_action
defines if the node should be
restarted (init:restart()
) or rebooted
(init:reboot()
) in case of an error during
the installation. Default is restart
.
The option code_change_timeout
defines the timeout
for all calls to sys:change_code
. If no value is
specified or default
is given, the default value
defined in sys
is used.
The option suspend_timeout
defines the timeout for
all calls to sys:suspend
. If no value is specified,
the values defined by the Timeout
parameter of
the upgrade
or suspend
instructions are used.
If default
is specified, the default value defined in
sys
is used.
The option {update_paths,Bool}
indicates if all
application code paths should be updated (Bool==true
),
or if only code paths for modified applications should be
updated (Bool==false
, default). This option only has
effect for other application directories than the default
$ROOT/lib/App-Vsn
, that is, application directories
provided in the AppDirs
argument in a call to
create_RELEASES/4
or set_unpacked/2
.
Example: In the current version CurVsn
of a release,
the application directory of myapp
is
$ROOT/lib/myapp-1.0
. A new version NewVsn
is
unpacked outside the release handler, and the release handler
is informed about this with a call to:
release_handler:set_unpacked(RelFile, [{myapp,"1.0","/home/user"},...]). => {ok,NewVsn}
If NewVsn
is installed with the option
{update_paths,true}
, afterwards
code:lib_dir(myapp)
will return
/home/user/myapp-1.0
.
make_permanent(Vsn) -> ok | {error, Reason}
Vsn = string()
Reason = {bad_status, Status} | term()
Makes the specified version Vsn
of the release
permanent.
remove_release(Vsn) -> ok | {error, Reason}
Vsn = string()
Reason = {permanent, Vsn} | client_node | term()
Removes a release and its files from the system. The release must not be the permanent release. Removes only the files and directories not in use by another release.
reboot_old_release(Vsn) -> ok | {error, Reason}
Vsn = string()
Reason = {bad_status, Status} | term()
Reboots the system by making the old release permanent, and
calls init:reboot()
directly. The release must have
status old
.
set_removed(Vsn) -> ok | {error, Reason}
Vsn = string()
Reason = {permanent, Vsn} | term()
Makes it possible to handle removal of releases outside the release handler. Tells the release handler that the release is removed from the system. This function does not delete any files.
set_unpacked(RelFile, AppDirs) -> {ok, Vsn} | {error, Reason}
RelFile = string()
AppDirs = [{App, Vsn, Dir}]
App = atom()
Vsn = Dir = string()
Reason = term()
Makes it possible to handle unpacking of releases outside
the release handler. Tells the release handler that
the release is unpacked. Vsn
is extracted from
the release resource file RelFile
.
AppDirs
can be used to specify from where the modules
for the specified applications should be loaded. App
is
the name of an application, Vsn
is the version, and
Dir
is the name of the directory where App-Vsn
is located. The corresponding modules should be located under
Dir/App-Vsn/ebin
. The directories for applications not
specified in AppDirs
are assumed to be located in
$ROOT/lib
.
unpack_release(Name) -> {ok, Vsn} | {error, Reason}
Name = Vsn = string()
Reason = client_node | term()
Unpacks a release package Name.tar.gz
located in
the releases
directory.
Performs some checks on the package - for example checks that all mandatory files are present - and extracts its contents.
which_releases() -> [{Name, Vsn, Apps, Status}]
Name = Vsn = string()
Apps = ["App-Vsn"]
Status = unpacked | current | permanent | old
Returns all releases known to the release handler.
Application Upgrade/Downgrade
The following functions can be used to test upgrade and downgrade
of single applications (instead of upgrading/downgrading an entire
release). A script corresponding to relup
is created
on-the-fly, based on the .appup
file for the application,
and evaluated exactly in the same way as release_handler
does.
Warning!
These function is primarily intended for simplified testing of
of .appup
files. They are not run within the context of
the release_handler
process. They must therefore
not be used together with calls to
install_release/1,2
, as this will cause
release_handler
to end up in an inconsistent state.
No persistent information is updated, why these functions can be used on any Erlang node, embedded or not. Also, using these functions does not effect which code will be loaded in case of a reboot.
If the upgrade or downgrade fails, the application may end up in an inconsistent state.
Functions
upgrade_app(App, Dir) -> {ok, Unpurged} | restart_new_emulator | {error, Reason}
App = atom()
Dir = string()
Unpurged = [Module]
Module = atom()
Reason = term()
Upgrades an application App
from the current
version to a new version located in Dir
according to
the .appup
script.
App
is the name of the application, which must be
started. Dir
is the new library directory of
App
, the corresponding modules as well as
the .app
and .appup
files should be located
under Dir/ebin
.
The function looks in the .appup
file and tries to
find an upgrade script from the current version of
the application using
upgrade_script/2.
This script is evaluated using
eval_appup_script/4,
exactly in the same way as
install_release/1,2
does.
Returns {ok, Unpurged}
if evaluating the script is
successful, where Unpurged
is a list of unpurged
modules, or restart_new_emulator
if this instruction is
encountered in the script, or {error, Reason}
if
an error occurred when finding or evaluating the script.
downgrade_app(App, Dir) ->
downgrade_app(App, OldVsn, Dir) -> {ok, Unpurged} | restart_new_emulator | {error, Reason}
App = atom()
Dir = OldVsn = string()
Unpurged = [Module]
Module = atom()
Reason = term()
Downgrades an application App
from the current
version to a previous version OldVsn
located in
Dir
according to the .appup
script.
App
is the name of the application, which must be
started. OldVsn
is the previous version of
the application and can be omitted if Dir
is of
the format "App-OldVsn"
. Dir
is the library
directory of this previous version of App
,
the corresponding modules as well as the old .app
file
should be located under Dir/ebin
. The .appup
file should be located in the ebin
directory of
the current library directory of the application
(code:lib_dir(App)
).
The function looks in the .appup
file and tries to
find an downgrade script to the previous version of
the application using
downgrade_script/3.
This script is evaluated using
eval_appup_script/4,
exactly in the same way as
install_release/1,2
does.
Returns {ok, Unpurged}
if evaluating the script is
successful, where Unpurged
is a list of unpurged
modules, or restart_new_emulator
if this instruction is
encountered in the script, or {error, Reason}
if
an error occurred when finding or evaluating the script.
upgrade_script(App, Dir) -> {ok, NewVsn, Script}
App = atom()
Dir = string()
NewVsn = string()
Script = Instructions -- see appup(4)
Tries to find an application upgrade script for App
from the current version to a new version located in
Dir
.
The upgrade script can then be evaluated using eval_appup_script/4. It is recommended to use upgrade_app/2 instead, but this function is useful in order to inspect the contents of the script.
App
is the name of the application, which must be
started. Dir
is the new library directory of
App
, the corresponding modules as well as
the .app
and .appup
files should be located
under Dir/ebin
.
The function looks in the .appup
file and tries to
find an upgrade script from the current version of
the application. High-level instructions are translated to
low-level instructions and the instructions are sorted in
the same manner as when generating a relup
script.
Returns {ok, NewVsn, Script}
if successful, where
NewVsn
is the new application version.
Failure: If a script cannot be found, the function fails with an appropriate error reason.
downgrade_script(App, OldVsn, Dir) -> {ok, Script}
App = atom()
OldVsn = Dir = string()
Script = Instructions -- see appup(4)
Tries to find an application downgrade script for App
from the current version to a previous version OldVsn
located in Dir
.
The downgrade script can then be evaluated using eval_appup_script/4. It is recommended to use downgrade_app/2,3 instead, but this function is useful in order to inspect the contents of the script.
App
is the name of the application, which must be
started. Dir
is the previous library directory of
App
, the corresponding modules as well as
the old .app
file should be located under
Dir/ebin
. The .appup
file should be located in
the ebin
directory of the current library
directory of the application (code:lib_dir(App)
).
The function looks in the .appup
file and tries to
find an downgrade script from the current version of
the application. High-level instructions are translated to
low-level instructions and the instructions are sorted in
the same manner as when generating a relup
script.
Returns {ok, Script}
if successful.
Failure: If a script cannot be found, the function fails with an appropriate error reason.
eval_appup_script(App, ToVsn, ToDir, Script) -> {ok, Unpurged} | restart_new_emulator | {error, Reason}
App = atom()
ToVsn = ToDir = string()
Script -- see upgrade_script/2, downgrade_script/3
Unpurged = [Module]
Module = atom()
Reason = term()
Evaluates an application upgrade or downgrade script
Script
, the result from calling
upgrade_app/2 or
downgrade_app/2,3,
exactly in the same way as
install_release/1,2
does.
App
is the name of the application, which must be
started. ToVsn
is the version to be upgraded/downgraded
to, and ToDir
is the library directory of this version.
The corresponding modules as well as the .app
and
.appup
files should be located under Dir/ebin
.
Returns {ok, Unpurged}
if evaluating the script is
successful, where Unpurged
is a list of unpurged
modules, or restart_new_emulator
if this instruction is
encountered in the script, or {error, Reason}
if
an error occurred when evaluating the script.
Typical Error Reasons
-
{bad_masters, Masters}
- The master nodesMasters
are not alive. -
{bad_rel_file, File}
- Specified.rel
fileFile
can not be read, or does not contain a single term. -
{bad_rel_data, Data}
- Specified.rel
file does not contain a recognized release specification, but another termData
. -
{bad_relup_file, File}
- Specifiedrelup
fileRelup
contains bad data. -
{cannot_extract_file, Name, Reason}
- Problems when extracting from a tar file,erl_tar:extract/2
returned{error, {Name, Reason}}
. -
{existing_release, Vsn}
- Specified release versionVsn
is already in use. -
{Master, Reason, When}
- Some operation, indicated by the termWhen
, failed on the master nodeMaster
with the specified error reasonReason
. -
{no_matching_relup, Vsn, CurrentVsn}
- Cannot find a script for up/downgrading betweenCurrentVsn
andVsn
. -
{no_such_directory, Path}
- The directoryPath
does not exist. -
{no_such_file, Path}
- The pathPath
(file or directory) does not exist. -
{no_such_file, {Master, Path}}
- The pathPath
(file or directory) does not exist at the master nodeMaster
. -
{no_such_release, Vsn}
- The specified versionVsn
of the release does not exist. -
{not_a_directory, Path}
-Path
exists, but is not a directory. -
{Posix, File}
- Some file operation failed forFile
.Posix
is an atom named from the Posix error codes, such asenoent
,eacces
oreisdir
. Seefile(3)
. -
Posix
- Some file operation failed, as above.
SEE ALSO
OTP Design Principles, config(4), relup(4), rel(4), script(4), sys(3), systools(3)