App-migrate
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NAME
App::migrate - upgrade / downgrade project
VERSION
This document describes App::migrate version v0.2.6
SYNOPSIS
use App::migrate;
my $migrate = App::migrate->new()
$migrate = $migrate->load($file)
@paths = $migrate->find_paths($v_from => $v_to)
say "versions: @{$_}" for @paths;
@steps = $migrate->get_steps($paths[0])
for (@steps) {
say "$_->{prev_version} ... $_->{next_version}";
if ($_->{type} eq 'VERSION' or $_->{type} eq 'RESTORE') {
say "$_->{type} $_->{version}";
} else {
say "$_->{type} $_->{cmd} @{$_->{args}}";
}
}
$migrate = $migrate->on(BACKUP => sub{ my $step=shift; return or die });
$migrate = $migrate->on(RESTORE => sub{ my $step=shift; return or die });
$migrate = $migrate->on(VERSION => sub{ my $step=shift; return or die });
$migrate = $migrate->on(error => sub{ my $step=shift; return or die });
$migrate->run($paths[0]);
DESCRIPTION
If you're looking for command-line tool - see migrate. This module is
actual implementation of that tool's functionality and you'll need it
only if you're developing similar tool (like narada-install) to
implement specifics of your project in single perl script instead of
using several external scripts.
This module implements file format (see "SYNTAX") to describe sequence
of upgrade and downgrade operations needed to migrate something between
different versions, and API to analyse and run these operations.
The something mentioned above is usually some project, but it can be
literally anything - OS configuration in /etc, or overall OS setup
including installed packages, etc. - anything what has versions and
need complex operations to upgrade/downgrade between these versions.
For example, to migrate source code you can use VCS like Git or
Mercurial, but they didn't support empty directories, file permissions
(except executable), non-plain file types (FIFO, UNIX socket, etc.),
xattr, ACL, configuration files which must differ on each site, and
databases. So, if you need to migrate anything isn't supported by VCS -
you can try this module/tool.
Sometimes it isn't possible to really downgrade because some data was
lost while upgrade - to handle these situations you should provide a
ways to create complete backup of your project and restore any
project's version from these backups while downgrade (of course,
restoring backups will result in losing new changes, so whenever
possible it's better to do some extra work to provide a way to
downgrade without losing any data).
Example
Here is example how to run migration from version '1.1.8' to '1.2.3' of
some project which uses even minor versions '1.0.x' and '1.2.x' for
stable releases and odd minor versions '1.1.x' for unstable releases.
The nearest common version between '1.1.8' and '1.2.3' is '1.0.42',
which was the parent for both '1.1.x' and '1.2.x' branches, so we need
to downgrade project from '1.1.8' to '1.0.42' first, and then upgrade
from '1.0.42' to '1.2.3'. You'll need two *.migrate files, one which
describe migrations from '1.0.42' (or earlier version) to '1.1.8', and
another with migrations from '1.0.42' (or earlier) to '1.2.3'. For
brevity let's not make any backups while migration.
my $migrate = App::migrate
->new
->load('1.1.8.migrate')
->load('1.2.3.migrate');
$migrate
->on(BACKUP => sub {})
->run( $migrate->find_paths('1.1.8' => '1.2.3') );
INTERFACE
new
$migrate = App::migrate->new;
Create and return new App::migrate object.
load
$migrate->load('path/to/migrate');
Load migration commands into $migrate object.
You should load at least one file with migration commands before you
can use "find_paths", "get_steps" or "run".
When loading multiple files, if they contain two adjoining 'VERSION'
operations with same version values then migration commands between
these two version values will be used from first loaded file containing
these version values.
Will throw if given file's contents don't conform to "Specification" -
this may be used to check file's syntax.
find_paths
@paths = $migrate->find_paths($from_version => $to_version);
Find and return all possible paths to migrate between given versions.
If no paths found - return empty list. This may happens because you
didn't loaded migrate files which contain required migrations or
because there is no way to migrate between these versions (for example,
if one of given versions is incorrect).
Multiple paths can be found, for example, when your project had some
branches which was later merged.
Each found path returned as single ARRAYREF element in returned list.
This ARRAYREF contains list of all intermediate versions, one by one,
starting from $from_version and ending with $to_version.
For example, if our project have this version history:
1.0.0
|
1.0.42
/ \
1.1.0 1.2.0
| |
1.1.10.migrate 1.0.0->…->1.0.42->1.1.0->…->1.1.10
1.2.5.migrate 1.0.0->…->1.0.42->1.2.0->…->1.2.3->1.2.4->1.2.5
1.1.8-1.2.4.migrate 1.0.0->…->1.0.42->1.1.0->…->1.1.8->1.2.4
If you "load" files 1.2.5.migrate and 1.1.8-1.2.4.migrate and then call
find_paths('1.0.42' => '1.2.5'), then it will return this list with two
paths (in any order):
(
['1.0.42', '1.1.0', …, '1.1.8', '1.2.4', '1.2.5'],
['1.0.42', '1.2.0', …, '1.2.3', '1.2.4', '1.2.5'],
)
get_steps
@steps = $migrate->get_steps( \@versions );
Return list of all migration operations needed to migrate on path given
in @versions.
For example, to get steps for first path returned by "find_paths":
@steps = $migrate->get_steps( $migrate->find_paths($from=>$to) );
Steps returned in order they'll be executed while "run" for this path.
Each element in @steps is a HASHREF with these keys:
type => one of these values:
'VERSION', 'before_upgrade', 'upgrade',
'downgrade', 'after_downgrade', 'RESTORE'
# these keys exists only if value of type key is one of:
# VERSION, RESTORE
version => version number
# these keys exists only if value of type key is one of:
# before_upgrade, upgrade, downgrade, after_downgrade
cmd => command to run
args => ARRAYREF of params for that command
Will throw if unable to return requested steps.
on
$migrate = $migrate->on(BACKUP => \&your_handler);
$migrate = $migrate->on(RESTORE => \&your_handler);
$migrate = $migrate->on(VERSION => \&your_handler);
$migrate = $migrate->on(error => \&your_handler);
Set handler for given event.
All handlers will be called only by "run"; they will get single
parameter - step HASHREF (BACKUP handler will get step in same format
as RESTORE), see "get_steps" for details of that HASHREF contents. Also
these handlers may use $ENV{MIGRATE_PREV_VERSION} and
$ENV{MIGRATE_NEXT_VERSION} - see "run" for more details.
'BACKUP' event
Handler will be executed when project backup should be created:
before starting any new migration, except next one after RESTORE.
If handler throws then 'error' handler will be executed.
Default handler will throw (because it doesn't know how to backup
your project).
NOTE: If you'll use handler which doesn't really create and keep
backups for all versions then it will be impossible to do RESTORE
operation.
'RESTORE' event
Handler will be executed when project should be restored from backup:
when downgrading between versions which contain RESTORE operation or
when migration fails.
If handler throws then 'error' handler will be executed.
Default handler will throw (because it doesn't know how to restore
your project).
'VERSION' event
Handler will be executed after each successful migration.
If handler throws then 'error' handler will be executed.
Default handler does nothing.
'error' event
Handler will be executed when one of commands executed while
migration fails or when BACKUP, RESTORE or VERSION handlers throw.
If handler throws then try to restore version-before-migration
(without calling error handler again if it throws too).
Default handler will run $SHELL (to let you manually fix errors) and
throw if you $SHELL exit status != 0 (to let you choose what to do
next - continue migration if you fixed error or interrupt migration
to restore version-before-migration from backup).
run
$migrate->run( \@versions );
Will use "get_steps" to get steps for path given in @versions and
execute them in order. Will also call handlers as described in "on".
Before executing each step will set $ENV{MIGRATE_PREV_VERSION} to
current version (which it will migrate from) and
$ENV{MIGRATE_NEXT_VERSION} to version it is trying to migrate to.
SYNTAX
Goals
Syntax of this file was designed to accomplish several goals:
* Be able to automatically make sure each 'upgrade' operation has
corresponding 'downgrade' operation (so it won't be forget - but, of
course, it's impossible to automatically check is 'downgrade'
operation will correctly undo effect of 'upgrade' operation).
Thus custom file format is needed.
* Make it easier to manually analyse is 'downgrade' operation looks
correct for corresponding 'upgrade' operation.
Thus related 'upgrade' and 'downgrade' operations must go one right
after another.
* Make it obvious some version can't be downgraded and have to be
restored from backup.
Thus RESTORE operation is named in upper case.
* Given all these requirements try to make it simple and obvious to
define migrate operations, without needs to write downgrade code for
typical cases.
Thus it's possible to define macro to turn combination of
upgrade/downgrade operations into one user-defined operation (no
worries here: these macro doesn't support recursion, it isn't
possible to redefine them, and they have lexical scope - from
definition to the end of this file - so they won't really add
complexity).
Example
VERSION 0.0.0
# To upgrade from 0.0.0 to 0.1.0 we need to create new empty file and
# empty directory.
upgrade touch empty_file
downgrade rm empty_file
upgrade mkdir empty_dir
downgrade rmdir empty_dir
VERSION 0.1.0
# To upgrade from 0.1.0 to 0.2.0 we need to drop old database. This
# change can't be undone, so only way to downgrade from 0.2.0 is to
# restore 0.1.0 from backup.
upgrade rm useless.db
RESTORE
VERSION 0.2.0
# To upgrade from 0.2.0 to 1.0.0 we need to run several commands,
# and after downgrading we need to kill some background service.
before_upgrade
patch <0.2.0.patch >/dev/null
chmod +x some_daemon
downgrade
patch -R <0.2.0.patch >/dev/null
upgrade
./some_daemon &
after_downgrade
killall -9 some_daemon
VERSION 1.0.0
# Let's define some lazy helpers:
DEFINE2 only_upgrade
upgrade
downgrade true
DEFINE2 mkdir
upgrade
mkdir "$@"
downgrade
rm -rf "$@"
# ... and use it:
only_upgrade
echo "Just upgraded to $MIGRATE_NEXT_VERSION"
VERSION 1.0.1
# another lazy macro (must be defined above in same file)
mkdir dir1 dir2
VERSION 1.1.0
Specification
Recommended name for file with upgrade/downgrade operations is either
migrate or <version>.migrate.
Each line in migrate file must be one of these:
* line start with symbol "#"
For comments. Line is ignored.
* line start with any non-space symbol, except "#"
Contain one or more elements separated by one or more space symbols:
operation name (case-sensitive), zero or more params (any param may
be quoted, params which contain one of 5 symbols "\\\"\t\r\n" must be
quoted).
Quoted params must be surrounded by double-quote symbol, and any of
mentioned above 5 symbols must be escaped like shown above.
* line start with two spaces
Zero or more such lines after line with operation name form one more,
multiline, extra param for that operation (first two spaces will be
removed from start of each line before providing this param to
operation).
Not all operations may have such multiline param.
* empty line
If this line is between operations then it's ignored.
If this line is inside operation's multiline param - then that
multiline param will include this empty line.
If you will need to include empty line at end of multiline param then
you'll have to use line with two spaces instead.
While executing any commands two environment variables will be set:
$MIGRATE_PREV_VERSION and $MIGRATE_NEXT_VERSION (first is always
version we're migrating from, and second is always version we're
migrating to - i.e. while downgrading $MIGRATE_NEXT_VERSION will be
lower/older version than $MIGRATE_PREV_VERSION)
All executed commands must complete without error, otherwise emergency
shell will be started and user should either fix the error and exit
from shell to continue migration, or exit 1 from shell to interrupt
migration and restore previous-before-this-migration version from
backup.
Supported operations
VERSION
Must have exactly one param (version number). Some symbols are not
allowed in version numbers: special (0x00-0x1F,0x7F), both slash, all
three quotes, ?, * and space.
Multiline param not supported.
This is delimiter between sequences of migrate operations.
Each file must contain 'VERSION' operation before any migrate
operations (i.e. before first 'VERSION' operation only 'DEFINE',
'DEFINE2' and 'DEFINE4' operations are allowed).
All operations after last 'VERSION' operation will be ignored.
before_upgrade
upgrade
downgrade
after_downgrade
These operations must be always used in pairs: first must be one of
'before_upgrade' or 'upgrade' operation, second must be one of
'downgrade' or 'after_downgrade' or 'RESTORE' operations.
These four operations may have zero or more params and optional
multiline param. If they won't have any params at all they'll be
processed like they have one (empty) multiline param.
Their params will be executed as a single shell command at different
stages of migration process and in different order:
* On each migration only commands between two nearest VERSION
operations will be processed.
* On upgrading (migrate forward from previous VERSION to next
VERSION) will be executed all 'before_upgrade' operations in forward
order then all 'upgrade' operations in forward order.
* On downgrading (migrate backward from next VERSION to previous)
will be executed all 'downgrade' operations in backward order, then
all 'after_downgrade' operations in backward order.
Shell command to use will be:
* If operation has one or more params - first param will become
executed command name, other params will become command params.
If operation also has multiline param then it content will be saved
into temporary file and name of that file will be added at end of
command's params.
* Else multiline param will be saved into temporary file (after
shebang #!/path/to/bash -ex if first line of multiline param doesn't
start with #!), which will be made executable and run without any
params.
RESTORE
Doesn't support any params, neither usual nor multiline.
Can be used only after 'before_upgrade' or 'upgrade' operations.
When one or more 'RESTORE' operations are used between some 'VERSION'
operations then all 'downgrade' and 'after_downgrade' operations
between same 'VERSION' operations will be ignored and on downgrading
previous version will be restored from backup.
DEFINE
This operation must have only one non-multiline param - name of defined
macro. This name must not be same as one of existing operation names,
both documented here or created by one of previous 'DEFINE' or
'DEFINE2' or 'DEFINE4' operations.
Next operation must be one of 'before_upgrade', 'upgrade', 'downgrade'
or 'after_downgrade' - it will be substituted in place of all next
operations matching name of this macro.
When substituting macro it may happens what both this macro definition
have some normal params and multiline param, and substituted operation
also have some it's own normal params and multiline param. All these
params will be combined into single command and it params in this way:
* If macro definition doesn't have any params - params of substituted
operation will be handled as usually for 'upgrade' etc. operations.
* If macro definition have some params - they will be handled as
usually for 'upgrade' etc. operations, so we'll always get some
command and optional params for it.
Next, all normal params of substituted command (if any) will be
appended to that command params.
Next, if substituted command have multiline param then it will be
saved to temporary file and name of that file will be appended to
that command params.
DEFINE2
Work similar to DEFINE, but require two next operations after it: first
must be one of 'before_upgrade' or 'upgrade', and second must be one of
'downgrade' or 'after_downgrade'.
Params of both operations will be combined with params of substituted
operation as explained above.
DEFINE4
Work similar to DEFINE, but require four next operations after it:
first must be 'before_upgrade', second - 'upgrade', third -
'downgrade', fourth - 'after_downgrade'.
Params of all four operations will be combined with params of
substituted operation as explained above.
SUPPORT
Bugs / Feature Requests
Please report any bugs or feature requests through the issue tracker at
https://github.com/powerman/migrate/issues. You will be notified
automatically of any progress on your issue.
Source Code
This is open source software. The code repository is available for
( run in 0.929 second using v1.01-cache-2.11-cpan-39bf76dae61 )