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NAME
appup - Application upgrade file
DESCRIPTION
The application upgrade file defines how an application is upgraded or downgraded in a
running system.
This file is used by the functions in systools when generating a release upgrade file
relup.
FILE SYNTAX
The application upgrade file is to be called Application.appup, where Application is the
application name. The file is to be located in the ebin directory for the application.
The .appup file contains one single Erlang term, which defines the instructions used to
upgrade or downgrade the application. The file has the following syntax:
{Vsn,
[{UpFromVsn, Instructions}, ...],
[{DownToVsn, Instructions}, ...]}.
Vsn = string():
Current application version.
UpFromVsn = string() | binary():
An earlier application version to upgrade from. If it is a string, it is interpreted
as a specific version number. If it is a binary, it is interpreted as a regular
expression that can match multiple version numbers.
DownToVsn = string() | binary():
An earlier application version to downgrade to. If it is a string, it is interpreted
as a specific version number. If it is a binary, it is interpreted as a regular
expression that can match multiple version numbers.
Instructions:
A list of release upgrade instructions, see Release Upgrade Instructions. It is
recommended to use high-level instructions only. These are automatically translated to
low-level instructions by systools when creating the relup file.
To avoid duplication of upgrade instructions, it is allowed to use regular expressions to
specify UpFromVsn and DownToVsn. To be considered a regular expression, the version
identifier must be specified as a binary. For example, the following match all versions
2.1.x, where x is any number:
<<"2\\.1\\.[0-9]+">>
Notice that the regular expression must match the complete version string, so this example
works for, for example, 2.1.1, but not for 2.1.1.1.
RELEASE UPGRADE INSTRUCTIONS
Release upgrade instructions are interpreted by the release handler when an upgrade or
downgrade is made. For more information about release handling, see OTP Design Principles
in System Documentation.
A process is said to use a module Mod if Mod is listed in the Modules part of the child
specification used to start the process, see supervisor(3erl). In the case of gen_event,
an event manager process is said to use Mod if Mod is an installed event handler.
High-Level Instructions
{update, Mod}
{update, Mod, supervisor}
{update, Mod, Change}
{update, Mod, DepMods}
{update, Mod, Change, DepMods}
{update, Mod, Change, PrePurge, PostPurge, DepMods}
{update, Mod, Timeout, Change, PrePurge, PostPurge, DepMods}
{update, Mod, ModType, Timeout, Change, PrePurge, PostPurge, DepMods}
Mod = atom()
ModType = static | dynamic
Timeout = int()>0 | default | infinity
Change = soft | {advanced,Extra}
Extra = term()
PrePurge = PostPurge = soft_purge | brutal_purge
DepMods = [Mod]
Synchronized code replacement of processes using module Mod.
All those processes are suspended using sys:suspend, the new module version is loaded, and
then the processes are resumed using sys:resume.
Change:
Defaults to soft and defines the type of code change. If it is set to
{advanced,Extra}, implemented processes using gen_server, gen_fsm, gen_statem, or
gen_event transform their internal state by calling the callback function code_change.
Special processes call the callback function system_code_change/4. In both cases, the
term Extra is passed as an argument to the callback function.
PrePurge:
Defaults to brutal_purge. It controls what action to take with processes executing old
code before loading the new module version. If the value is brutal_purge, the
processes are killed. If the value is soft_purge, release_handler:install_release/1
returns {error,{old_processes,Mod}}.
PostPurge:
Defaults to brutal_purge. It controls what action to take with processes that are
executing old code when the new module version has been loaded. If the value is
brutal_purge, the code is purged when the release is made permanent and the processes
are killed. If the value is soft_purge, the release handler purges the old code when
no remaining processes execute the code.
DepMods:
Defaults to [] and defines other modules that Mod is dependent on. In the relup file,
instructions for suspending processes using Mod come before instructions for
suspending processes using modules in DepMods when upgrading, and conversely when
downgrading. In case of circular dependencies, the order of the instructions in the
appup file is kept.
Timeout:
Defines the time-out when suspending processes. If no value or default is specified,
the default value for sys:suspend is used.
ModType:
Defaults to dynamic. It specifies if the code is "dynamic", that is, if a process
using the module spontaneously switches to new code, or if it is "static". When doing
an advanced update and upgrade, the new version of a dynamic module is loaded before
the process is asked to change code. When downgrading, the process is asked to change
code before loading the new version. For static modules, the new version is loaded
before the process is asked to change code, both in the case of upgrading and
downgrading. Callback modules are dynamic.
update with argument supervisor is used when changing the start specification of a
supervisor.
{load_module, Mod}
{load_module, Mod, DepMods}
{load_module, Mod, PrePurge, PostPurge, DepMods}
Mod = atom()
PrePurge = PostPurge = soft_purge | brutal_purge
DepMods = [Mod]
Simple code replacement of the module Mod.
For a description of PrePurge and PostPurge, see update above.
DepMods defaults to [] and defines which other modules Mod is dependent on. In the relup
file, instructions for loading these modules come before the instruction for loading Mod
when upgrading, and conversely when downgrading.
{add_module, Mod}
{add_module, Mod, DepMods}
Mod = atom()
DepMods = [Mod]
Loads a new module Mod.
DepMods defaults to [] and defines which other modules Mod is dependent on. In the relup
file, instructions related to these modules come before the instruction for loading Mod
when upgrading, and conversely when downgrading.
{delete_module, Mod}
{delete_module, Mod, DepMods}
Mod = atom()
Deletes a module Mod using the low-level instructions remove and purge.
DepMods defaults to [] and defines which other modules Mod is dependent on. In the relup
file, instructions related to these modules come before the instruction for removing Mod
when upgrading, and conversely when downgrading.
{add_application, Application}
{add_application, Application, Type}
Application = atom()
Type = permanent | transient | temporary | load | none
Adding an application means that the modules defined by the modules key in the .app file
are loaded using add_module.
Type defaults to permanent and specifies the start type of the application. If Type =
permanent | transient | temporary, the application is loaded and started in the
corresponding way, see application(3erl). If Type = load, the application is only loaded.
If Type = none, the application is not loaded and not started, although the code for its
modules is loaded.
{remove_application, Application}
Application = atom()
Removing an application means that the application is stopped, the modules are unloaded
using delete_module, and then the application specification is unloaded from the
application controller.
{restart_application, Application}
Application = atom()
Restarting an application means that the application is stopped and then started again,
similar to using the instructions remove_application and add_application in sequence. Note
that, even if the application has been started before the release upgrade is performed,
restart_application may only load it rather than start it, depending on the application's
start type: If Type = load, the application is only loaded. If Type = none, the
application is not loaded and not started, although the code for its modules is loaded.
Low-Level Instructions
{load_object_code, {App, Vsn, [Mod]}}
App = Mod = atom()
Vsn = string()
Reads each Mod from directory App-Vsn/ebin as a binary. It does not load the modules. The
instruction is to be placed first in the script to read all new code from the file to make
the suspend-load-resume cycle less time-consuming.
point_of_no_return
If a crash occurs after this instruction, the system cannot recover and is restarted from
the old release version. The instruction must only occur once in a script. It is to be
placed after all load_object_code instructions.
{load, {Mod, PrePurge, PostPurge}}
Mod = atom()
PrePurge = PostPurge = soft_purge | brutal_purge
Before this instruction occurs, Mod must have been loaded using load_object_code. This
instruction loads the module. PrePurge is ignored. For a description of PostPurge, see the
high-level instruction update earlier.
{remove, {Mod, PrePurge, PostPurge}}
Mod = atom()
PrePurge = PostPurge = soft_purge | brutal_purge
Makes the current version of Mod old. PrePurge is ignored. For a description of PostPurge,
see the high-level instruction update earlier.
{purge, [Mod]}
Mod = atom()
Purges each module Mod, that is, removes the old code. Notice that any process executing
purged code is killed.
{suspend, [Mod | {Mod, Timeout}]}
Mod = atom()
Timeout = int()>0 | default | infinity
Tries to suspend all processes using a module Mod. If a process does not respond, it is
ignored. This can cause the process to die, either because it crashes when it
spontaneously switches to new code, or as a result of a purge operation. If no Timeout is
specified or default is specified, the default value for sys:suspend is used.
{resume, [Mod]}
Mod = atom()
Resumes all suspended processes using a module Mod.
{code_change, [{Mod, Extra}]}
{code_change, Mode, [{Mod, Extra}]}
Mod = atom()
Mode = up | down
Extra = term()
Mode defaults to up and specifies if it is an upgrade or downgrade. This instruction sends
a code_change system message to all processes using a module Mod by calling function
sys:change_code, passing term Extra as argument.
{stop, [Mod]}
Mod = atom()
Stops all processes using a module Mod by calling supervisor:terminate_child/2. This
instruction is useful when the simplest way to change code is to stop and restart the
processes that run the code.
{start, [Mod]}
Mod = atom()
Starts all stopped processes using a module Mod by calling supervisor:restart_child/2.
{sync_nodes, Id, [Node]}
{sync_nodes, Id, {M, F, A}}
Id = term()
Node = node()
M = F = atom()
A = [term()]
apply(M, F, A) must return a list of nodes.
This instruction synchronizes the release installation with other nodes. Each Node must
evaluate this command with the same Id. The local node waits for all other nodes to
evaluate the instruction before execution continues. If a node goes down, it is considered
to be an unrecoverable error, and the local node is restarted from the old release. There
is no time-out for this instruction, which means that it can hang forever.
{apply, {M, F, A}}
M = F = atom()
A = [term()]
Evaluates apply(M, F, A).
If the instruction appears before instruction point_of_no_return, a failure is caught.
release_handler:install_release/1 then returns {error,{'EXIT',Reason}}, unless
{error,Error} is thrown or returned. Then it returns {error,Error}.
If the instruction appears after instruction point_of_no_return and the function call
fails, the system is restarted.
restart_new_emulator
This instruction is used when the application ERTS, Kernel, STDLIB, or SASL is upgraded.
It shuts down the current emulator and starts a new one. All processes are terminated
gracefully, and the new version of ERTS, Kernel, STDLIB, and SASL are used when the
emulator restarts. Only one restart_new_emulator instruction is allowed in the relup file,
and it must be placed first. systools:make_relup/3,4 ensures this when the relup file is
generated. The rest of the instructions in the relup file is executed after the restart as
a part of the boot script.
An info report is written when the upgrade is completed. To programmatically determine if
the upgrade is complete, call release_handler:which_releases/0,1 and check if the expected
release has status current.
The new release must still be made permanent after the upgrade is completed, otherwise the
old emulator is started if there is an emulator restart.
Warning:
As stated earlier, instruction restart_new_emulator causes the emulator to be restarted
with new versions of ERTS>, Kernel, STDLIB, and SASL. However, all other applications do
at startup run their old versions in this new emulator. This is usually no problem, but
every now and then incompatible changes occur to the core applications, which can cause
trouble in this setting. Such incompatible changes (when functions are removed) are
normally preceded by a deprecation over two major releases. To ensure that your
application is not crashed by an incompatible change, always remove any call to deprecated
functions as soon as possible.
restart_emulator
This instruction is similar to restart_new_emulator, except it must be placed at the end
of the relup file. It is not related to an upgrade of the emulator or the core
applications, but can be used by any application when a complete reboot of the system is
required.
When generating the relup file, systools:make_relup/3,4 ensures that there is only one
restart_emulator instruction and that it is the last instruction in the relup file.
SEE ALSO
release_handler(3erl), relup(5), supervisor(3erl), systools(3erl)