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release_handler(3erl) | Erlang Module Definition | release_handler(3erl) |
NAME¶
release_handler - Unpacking and Installation of Release PackagesDESCRIPTION¶
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. The installation of 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 version of the release. 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(7) 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.
EXPORTS¶
check_install_release(Vsn) -> {ok, OtherVsn, Descr} | {error, Reason}
Types:
Vsn = OtherVsn = string()
Opts = [Opt]
Opt = purge
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.
If the option purge is given, all old code that can be soft purged will
be purged after all other checks are successfully completed. This can be
useful in order to reduce the time needed by install_release.
create_RELEASES(Root, RelDir, RelFile, AppDirs) -> ok | {error,
Reason}
Types:
Root = RelDir = RelFile = string()
AppDirs = [{App, Vsn, Dir}]
App = atom()
Vsn = Dir = string()
Reason = term()
App = atom()
Vsn = Dir = string()
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}
Types:
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}
Types:
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()} | {missing_base_app, OtherVsn, App} | {could_not_create_hybrid_boot,
term()} | term()
App = atom()
| {suspend_timeout, Timeout} | {update_paths, Bool}
Action = restart | reboot
Timeout = default | infinity | int()>0
Bool = boolean()
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 {continue_after_restart,OtherVsn,Descr} is returned, it means that the
emulator will be restarted before the upgrade instructions are executed. This
will happen if the emulator or any of the applications kernel, stdlib or sasl
are updated. The new version of the emulator and these core applications will
execute after the restart, but for all other applications the old versions
will be started and the upgrade will be performed as normal by executing the
upgrade instructions.
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:
make_permanent(Vsn) -> ok | {error, Reason}
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.
Note:
Installing a new release might be quite time consuming if there are many
processes in the system. The reason is that each process must be checked for
references to old code before a module can be purged. This check might lead to
garbage collections and copying of data.
If you wish to speed up the execution of install_release, then you may
call check_install_release first, using the option purge. This
will do the same check for old code, and then purge all modules that can be
soft purged. The purged modules will then no longer have any old code, and
install_release will not need to do the checks.
Obviously, this will not reduce the overall time for the upgrade, but it will
allow checks and purge to be executed in the background before the real
upgrade is started.
Note:
When upgrading the emulator from a version older than OTP R15, there will be an
attempt to load new application beam code into the old emulator. In some
cases, the new beam format can not be read by the old emulator, and so the
code loading will fail and terminate the complete upgrade. To overcome this
problem, the new application code should be compiled with the old emulator.
See Design Principles for more information about emulator upgrade from
pre OTP R15 versions.
Types:
Vsn = string()
Reason = {bad_status, Status} | term()
Makes the specified version Vsn of the release permanent.
remove_release(Vsn) -> ok | {error, Reason}
Types:
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}
Types:
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}
Types:
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}
Types:
RelFile = string()
AppDirs = [{App, Vsn, Dir}]
App = atom()
Vsn = Dir = string()
Reason = term()
App = atom()
Vsn = Dir = string()
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}
Types:
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}]
Types:
Name = Vsn = string()
Apps = ["App-Vsn"]
Status = unpacked | current | permanent | old
Returns all releases known to the release handler.
which_releases(Status) -> [{Name, Vsn, Apps, Status}]
Types:
Name = Vsn = string()
Apps = ["App-Vsn"]
Status = unpacked | current | permanent | old
Returns all releases known to the release handler of a specific status.
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 functions are primarily intended for simplified testing 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 affect
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.
EXPORTS¶
upgrade_app(App, Dir) -> {ok, Unpurged} | restart_emulator | {error, Reason}
Types:
App = atom()
Dir = string()
Unpurged = [Module]
Module = atom()
Reason = term()
Module = atom()
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_emulator if
this instruction is encountered in the script, or {error, Reason} if an
error occurred when finding or evaluating the script.
If the restart_new_emulator instruction is found in the script,
upgrade_app/2 will return {error,restart_new_emulator}. The
reason for this is that this instruction requires that a new version of the
emulator is started before the rest of the upgrade instructions can be
executed, and this can only be done by install_release/1,2.
downgrade_app(App, Dir) ->
Types:
App = atom()
Dir = OldVsn = string()
Unpurged = [Module]
Module = atom()
Reason = term()
Module = atom()
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_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}
Types:
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}
Types:
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_emulator | {error, Reason}
Types:
App = atom()
ToVsn = ToDir = string()
Script -- see upgrade_script/2, downgrade_script/3
Unpurged = [Module]
Module = atom()
Reason = term()
Module = atom()
Evaluates an application upgrade or downgrade script Script, the result
from calling upgrade_script/2 or downgrade_script/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_emulator if
this instruction is encountered in the script, or {error, Reason} if an
error occurred when evaluating the script.
If the restart_new_emulator instruction is found in the script,
eval_appup_script/4 will return {error,restart_new_emulator}.
The reason for this is that this instruction requires that a new version of
the emulator is started before the rest of the upgrade instructions can be
executed, and this can only be done by install_release/1,2.
TYPICAL ERROR REASONS¶
- *
- {bad_masters, Masters} - The master nodes Masters are not alive.
- *
- {bad_rel_file, File} - Specified .rel file File 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 term Data.
- *
- {bad_relup_file, File} - Specified relup file Relup 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 version Vsn is already in use.
- *
- {Master, Reason, When} - Some operation, indicated by the term When, failed on the master node Master with the specified error reason Reason.
- *
- {no_matching_relup, Vsn, CurrentVsn} - Cannot find a script for up/downgrading between CurrentVsn and Vsn.
- *
- {no_such_directory, Path} - The directory Path does not exist.
- *
- {no_such_file, Path} - The path Path (file or directory) does not exist.
- *
- {no_such_file, {Master, Path}} - The path Path (file or directory) does not exist at the master node Master.
- *
- {no_such_release, Vsn} - The specified version Vsn of the release does not exist.
- *
- {not_a_directory, Path} - Path exists, but is not a directory.
- *
- {Posix, File} - Some file operation failed for File. Posix is an atom named from the Posix error codes, such as enoent, eacces or eisdir. See file(3erl).
- *
- Posix - Some file operation failed, as above.
SEE ALSO¶
OTP Design Principles, config(5), relup(5), rel(5), script(5), sys(3erl), systools(3erl)sasl 2.4.1 | Ericsson AB |