=head1 NAME

git-deploy - automate the git steps required for a deploying code from a git repository

=head1 SYNOPSIS

    git deploy [deploy-options] [action [prefix]] [action-options]
    git deploy --man

    actions:
        status                   # show rollout status of current repository
        start|abort|sync|finish  # normal multi-server rollout sequence (finish is automatic if sync succeeds)
        start|abort|release      # normal single-server rollout sequence (when you don't need a sync hook)
        hotfix                   # Roll out the site with a hotfix (a.k.a. start without an automatic "git pull")
        revert                   # revert site to previous rollout (interactive - replaces start)
        manual-sync              # manual sync process (replaces sync - can be used for a gradual sync)
        show                     # show list of tags
        show-tag                 # show the currently deployed tag (if it exists)
        tag                      # create a tag for this commit (restricted to certain environments)
        log                      # during a rollout show log of changes since the last rollout
        diff                     # during a rollout show differences between previous rollout

=head1 NAVIGATION

=over

=item *

See L</DESCRIPTION> for an overview of what B<git-deploy> is all
about, and how it operates from a big picture perspective.

=item *

See L</ACTIONS> for the B<git-deploy> sub-commands. These are the
commands you'll be using on a daily (or hopefully less than hourly)
basis to do rollouts.

=item *

See L</OPTIONS> and L</OTHER OPTIONS> for common options you might
want to use, and increasingly obscure options you'll probably never
need, respectively.

=item *

See L</CONFIGURATION> for configuring B<git-deploy>. Unless you're the
sysadmin setting up the tool you don't need to worry about this.

=item *

See L</WRITING DEPLOY HOOKS> for how deploy hooks work. This is
relevant to you if you're the poor sob tasked with implementing said
hooks.

=back

=head1 DESCRIPTION

B<git-deploy> is a tool written to make deployments so easy that
you'll let new hires do them on their first day. Conceived and
introduced at Booking.com in 2008, it has changed deployments from being
something that took hours, to being so easy that deploying 20 times a
day is what happens (on a slow day).

It's highly configurable and pluggable. We use it for deploying
everything from single-server environments to deploying our main web
server cluster.

It creates an annotated git tag for every rollout, and pushes those tags
upstream, so anyone with a copy of the repository can see what's
deployed where. This is invaluable for debugging and tracking the
history of deployments.

It adheres to the Unix philosophy, being a tool that does one thing and,
does it well. It's fully pluggable (the hook API is just a bunch
of executable files with exit() values, you don't have to learn to use
a complicated API), it's easily scriptable, and it runs anywhere you
have a standard installation of Perl 5.8 or later.

But enough with the sales pitch, what does it actually do?

=over 8

=item *

git-deploy implements exclusive locking, i.e. it allows only one person to
deploy to an environment at the same time. This is how a deployment starts, and
you do this with:

    git-deploy start

...which will create a lock file and do "git pull" for you, to update your
local tree to include the latest upstream code.

This means that you have a repository somewhere that you do
deployments from. This is your staging server, or the only server you
have, it doesn't matter. It just has to be one standard location.

Under the hood locking is simply implemented with a
F<.git/deploy/lock> file - if users have configured their umask
correctly (and git-deploy can enforce this) you can forcibly take over
another user's deployments with C<--force>.

=item *

Once you're in the locked state you can do any git operation you'd
like. git-deploy doesn't care, you can "git pull", you can make new
commits (as long as you push them upstream before the sync step).

If you chicken out at this point you can always:

    git-deploy abort

Which'll get you back to the state you were in before you ran
L</start>.

When you're happy with the state of things you want to deploy, git-deploy will
create a tag to record in the commit history that the current state is what was
released, and then call your sync hooks (if any are configured):

    git-deploy sync

...which will create a tag, and roll it out to your network. The details of the
rollout itself are B<completely up to you> (see L</Sync Hooks>). You can use
everything from git itself to carrier pigeons, git-deploy doesn't care.

If the sync hook fails (e.g. because a cat ate your pigeon)
git-deploy exits with an error and expects to you fix the situation.

Usually fixing it is a combination of running the sync hook manually
again, and making a mental note to beat your sysadmins with a
rake. 

If you prefer to perform the rollout yourself, you can instead use git-deploy
to simply tag a release and push that back to your main repository.

    git-deploy release

This is not a recommended way to use the tool since one of git-deploy's
functions is to manage the process of pushing code out to multiple production
boxes. Your life will be much easier if you choose to implement sync hooks
instead.

You'll have to set L</deploy.can-make-tags> to C<true> to use this.

Once you've done the former successfully:

    git-deploy finish

(...which "git-deploy release" and "git-deploy sync" do for you if you
haven't encountered an error.)

That'll perform any final actions (like sending an e-mail about your shiny
new deployment), and then unlock the deployment server so the next
poor sob who has to do a deployment can use it.

=back

Does that sound simple? Well that's because it is. It's a very simple
tool, it's so simple that we even allow designers to use it.

So why do you need it? Well partly because we've been lying to you up
until this point. The main feature of this tool is not actually doing
rollouts, it's doing reverts.

When you inevitably bork a rollout and you want to undo as fast
as possible, B<git-deploy> makes this really easy. You can run
B<git-deploy show> to see a history of recent rollouts, and you can use
B<git-deploy revert> to interactively revert to a previous revision.

This means that you get presented with a list of things that were
recently rolled out, and then have the chance to choose which should
be rolled out as a replacement. Once you select the synchronization
process is started and the bad code is replaced by whatever you have
selected.

When you manage to get even this wrong, and revert to the wrong commit
B<git-deploy> makes it easy to see exactly what happened and what you did, and
B<git-deploy show> will show you which of the several tags you've been jumping
back and forth between correspond to a given revision.  Once have figured out
which commit you should go to, use B<git-deploy revert> to roll it out.

The tool also performs very exhaustive error checking added over years of
trial and error, as its inexperienced users have tried to screw up
rollouts in every way possible.

If there is a problem in general the tool will detect it, and advise
you of what it is and how to deal with it.

It'll ensure that tags are created which you can roll back to, and
ensure that they are pushed afterwards.

B<git-deploy> will fetch all tags from the remote repository
configured in the current repository before processing. You can
disable this behaviour by using --no-remote which overrides all remote
actions.

In the case of an unclean working directory an error message will be
produced and the output of `git status` will be displayed. Note: This includes
untracked files, which must be either deleted or added to the
repository's F<.gitignore> (which itself must then be committed),
before you can proceed with using B<git-deploy>. You can disable this
with --no-check if you're feeling adventurous.

One thing it definitely doesn't do is worry about how your code gets
copied around to your production servers, that's completely up to you.

If you have some way of copying around code to be deployed (git
archive, rsync, building .deb or .rpm packages) that you use now you
can and should continue using it.

git-deploy solves the problem of making your deployment history
available in a distributed way to everyone with a Git checkout, as
well as making sure that there's an exclusive lock on deployments
while they're in progress (although you could skip that part if you
were feeling adventurous enough).

=head2 Deploy Files

A deploy file consists of a set of keys and values, followed by a newline,
followed by the deployment message used to create the deployment tag. For
instance:

    commit: 7e25a770901c9b1eb75ad1511580a98acff4ad60
    tag: sheep-20080827-1419
    deploy-date: 2008-08-27 14:19:58
    deployed-from: bountiful.farm.com
    deployed-by: rafael

    rollout of sheep

    <EOF>

If new key/values are added, they will always be added before the blank line.

=head2 Deploy Hooks

At various points in the deployment process F<git-deploy> can
execute user-supplied hooks.

This is to provide a mechanism by which actions and tests
will be automatically executed, and if necessary can prevent the
final sync step from occurring.

Hooks can be specific at the generic level (i.e. for all
environments), and on an environment-specific basis.

=head1 OPTIONS

Use git-deploy --man to see complete set of options and details of use.

=over 8

=item B<--force>

Force the action, and bypass most sanity checks. Do not use unless you know what you
are doing.

=item B<--verbose>

Emits progress information to STDERR during processing.

=item B<--help>

Print a brief help message and exits. (You are probably reading this output right now.)

=item B<--man>

Uses perldoc/man to output far far more than you ever realized there was to know about
using this tool.

=back

=head1 OTHER OPTIONS

=over 8

=item B<--message>=STRING

Message to use when creating a tag. Required when creating a new tag. Since you
can't know the name of the newly created tag when writing the message you can use
the special sequence C<%TAG> as a replacement.

=item B<--show-prefix>

Print to STDOUT whatever prefix would be used given the current arguments and then exit.
Throw an error if there would be no prefix.

=item B<--to-mail>=STRING

Address to use to send announcement mails to. Defaults to 'none'. See
L</deploy.announce-mail> for a config option to set this.

=item B<--show-deploy-file>

Prints the name of the current deploy file to STDOUT, if and only if the commit it contains
corresponds to HEAD. Otherwise prints nothing. Exits immediately afterwards.

=item B<--deploy-file-name>

Set the deploy file name. If this option is not provided the deploy file defaults to
C<./lib/.deploy> if a directory named C<./lib> exists, and otherwise to C<./.deploy>

=item B<--list>

=item B<--list-all>

Instead of printing out a single tagname for the current commit's tag, print out a
verbose list of tags, sorted by the date that they contain in order of most recent to
oldest. The output is structured like so:

    7e25a770901c.. *tag: sheep-20080827-1419
    2806eb24c3c2..  tag: cows-20080827-1240
    d6af6e1ad6f1..  tag: goats_20080826-1458
    889f65216880..  tag: goats_20080826-1034
    90318602f8d2..  tag: cows_20080826-1005
    6bd340c67bdb..  tag: sheep-20080825-2245
    19587c195a8b..  tag: sheep-20080825-2116 -> sheep-20080825-2105
    19587c195a8b..  tag: sheep-20080825-2105

The first column is the abbreviated commit SHA1 (abbreviation can be disabled
with the C<--long-digest> option), Followed by either C<< <space><space> >> or
by C<< <space><star> >>. The starred items correspond to HEAD. The arrow indicates
that there are two different tags to the same commit, and points to the oldest
equivalent tag. This is then followed by either 'tag:' or 'branch:' (depending on
whether C<--include-branches> is invoked) and then the item name. This may then be
followed by space and an arrow, and then a second name, which indicates that
the tag is a duplicate and shows the oldest displayed item. Undated items like
branches go last in alphabetic order, with some special exceptions for i.e. trunk or
master.

When used with just C<--list> mode, only starred items corresponding to HEAD are displayed,
--list-all shows unstarred items that do not correspond to HEAD as well.

=item B<--include-branches>

Show information about branches as well when in C<--list> mode

=item B<--long-digest>

Show full SHA1's when in C<--list> mode.

=item B<--ignore-older-than>=YYYYMMDD

Totally ignore tags which are from before this date. Defaults to C<20080101>.

Checking *every* tag to see if it corresponds to HEAD can be expensive. This options
makes it possible to filter old tags by date to avoid checking them when you know they
wont match.

=item B<--make-tag>

Make a tag. This is the same as the "tag" action except the tag will not be automatically
pushed.

=item B<--no-check-clean>

Do not check that the working directory is clean before doing things.

=item B<--no-remote>

Skip any actions that involve talking to a remote repository.

=item B<--remote-site>=STRING

Name of remote site to access when pushing, pulling or fetching. Defaults to 'origin'.

Using an remote site name of 'none' is the same as using --no-remote

=item B<--remote-branch>=STRING

Name of remote branch to access when pushing, pulling or fetching. Defaults to the current
branch, just like git pull or git push would.

=item B<--date-fmt>=FORMAT

Perl strfime() format to use in datestamped tags. Defaults to '%Y%m%d-%H%M'.
Changing this value is probably unwise, as various features of the deploy process
expect to be able to parse date stamps in this format.

=back

=head1 ACTIONS

=head2 start

Used to start a multi step rollout procedure. Remembers (and if necessary, tags) start
position as well as create locks to prevent two people from doing a procedure at the
same time. See C<hotfix> below for rollout out a hotfix on top of a previous rollout
tag.

=head2 sync

Used to declare that the current commit is ready for sync. This will automatically call
the appropriate sync command for this app, as defined in F<deploy/sync/$app.sync>.

=head2 abort

A command which can be used any time prior to the manual synchronization step which will
automatically end the rollout, restore the git working directory from the current state
to the start position. Note this is NOT the way to "rollback a rollout", it is the
way to abort a rollout prior to its completion.

I.e. if someone else has started a rollout and gone away you can do:

    git-deploy --force abort

And the state of the rollout machine will be reset back to what it was
before they ran C<git-deploy start>.

=head2 finish

Used to declare that the rollout session is finished, and that git-deploy
should push any new commits or tags, create the final emails of any changes
and perform related functions.

=head2 release

Used in the "two step" rollout process for boxes where there is no manual
synchronization step.

=head2 tag

Used in the "one step" rollout process to tag a commit and push it to the
remote.

=head2 revert

This is used to do an interactive "revert" of the site to a previous rollout.
It combines the steps "git-deploy start/git reset .../git-deploy
sync/git-deploy finish" into one, with interactive selection of the commit to
revert to. If sync hooks and deploy hooks are provided then they will be
automatically run as normal. If they aren't, a manual sync/finish is required.

=head2 show-tag

Show the tag for the current commit, if there is one.

=head2 status

Show the status of the deploy procedure. Can be used to check what step you are on.

=head2 hotfix

Here's how you can do a hotfix rollout, i.e. when you have an existing
rollout tag that you wish to apply a single commit (or several) onto.

First, instead of C<git-deploy start>, do:

    git-deploy hotfix

...which will start C<git-deploy> without performing a C<git pull>
beforehand. Then you cherry-pick some commit/s:

    git cherry-pick SHA1_OF_HOTFIX

...and make a note of the resulting <NEW_SHA1>:

    git --no-pager log -1 --pretty=%H

Then do a:

    git pull --no-rebase

Followed by:

    git push

to push your hotfix to the Git server. But now you're not at what you
want to roll out, so do:

    git reset --hard NEW_SHA1
    git checkout -f

This will ensure that you are on your hotfix commit, and that any git hooks are
executed. You should then TEST the code. On a webserver this normally involves

    httpd restart

followed by some manual testing of the relevant web site.

When you are satisfied that things are OK, you can execute the sync:

    git-deploy sync

B<TODO>: The last 3 pull/push/reset steps are busywork that should be, and eventually
will be merged into C<git-deploy sync>.

=head2 manual-sync

Declares the current commit is ready for sync, but will drop the user back into the shell
to execute the sync manually. It is then up to the user to execute the finish action when
they have deemed the rollout to be complete.

=head1 CONFIGURATION

git-deploy uses L<git(1)> to drive its configuration. This means that
if you're rolling out a given repository situated at F</some/path> you
can configure everything in F</some/path/.git/config> with
L<git-config(1)>.

We use the namespace C<deploy> for our configuration. See this section
for an overview of our configuration options, but you can also jump to
L</EXAMPLE CONFIGURATION> for an example of how to configure the tool.

These are L<git(1)> config options that need to be set, see
L<git-config(1)> for details:

=over

=item * user.name

=item * user.email

=back

And these are L<git-deploy(1)>-specific options:

=head3 deploy.log-directory

This is a directory where we emit a F<git-deploy.log> file and if
C<deploy.log-timing-data> is true we'll also emit timing data there.

=head3 deploy.log-timing-data

A boolean option that configures whether or not we log timing data,
off by default.

=head3 deploy.block-file

A path to a file which if existent will block rollouts,
e.g. F</etc/ROLLOUTS_BLOCKED>

=head3 deploy.can-make-tags

Can this environment make tags manually with C<git-deploy tag>? Used
for special purposes, you probably don't need this.

=head3 deploy.config-file

The C<git-deploy> config file, set this to e.g. C</etc/git-deploy.ini>
in C</etc/gitconfig> on the deployment box to have C<git-deploy> read
that config file.

We'll read the config file with C<git config --file> so you can
B<also> put stuff in C</etc/gitconfig>, C<.git/config> or any other
file Git normally reads.

=head3 deploy.deploy-file

This is a file we write out to the directory being deployed before the
C<sync> step to indicate what tag we've deployed, who deployed it
etc. See L</Deploy Files> for details.

This is F<.deploy> by default, but you can also set it to
e.g. F<lib/.deploy> in environments where only the lib/ directory is
synced out.

=head3 deploy.hook-dir

What directory do we look for our hooks in? See L</Deploy Hooks> for
details.

=head3 deploy.tag-prefix

A prefix we'll add to your tags, set to e.g. C<cron> for your cron
deploys, C<app> for your main web application. C<debug> is something
you can use to test the tool.

=head3 deploy.support-email

An e-mail address we'll tell the user to contact if the sync hook
fails. This'll be in the big "DON'T PANIC" message that we emit if the
sync hook fails.

=head3 deploy.mail-tool

The tool we use to send mail. C</usr/sbin/sendmail -f> by default.

=head3 deploy.restrict-umask

Force the user to have a given umask before they can invoke us.

=head3 deploy.announce-mail

An e-mail address that the below C<send-mail-on-*> mails will be sent
to.

=head3 deploy.send-mail-on-ACTION

A boolean option that configures when we send
mail. E.g. C<deploy.send-mail-on-start = true> will have mail sent
when we do "git-deploy start".

=head3 deploy.repo-name-detection

The strategy we'll use to detect the current repository
name. Currently only C<dot-git-parent-dir> is supported. See the
L</EXAMPLE CONFIGURATION> for how this is used.

=head3 deploy.lock-dir-root

Normally git-deploy tucks its lock file and reference data away in
the .git directory of the repo being deployed. It can be useful to
specify a common place for multiple repositories to share for this
purpose, providing an "interlock" behaviour that prevents more than
one of the repositories being rolled out at once.

=head3 deploy.message-on-sync-hook-fail-whale

A message you can specify which'll be output when we fail to run the
sync hook instead of the default message. You can put any
site-specific instructions here to replace the defaults.

The strings C<{SYNC_HOOK}> and C<{SUPPORT_EMAIL}> in that message will
be replaced with the sync hook that was run and the support E-Mail
specified in L</deploy.support-email>.

=head1 EXAMPLE CONFIGURATION

Here's an example git-deploy configuration that can deal with rolling
out more than one repository on a given box with a globally maintained
config file. First we set up C<deploy.config-file> in
F</etc/gitconfig>:

    $ cat /etc/gitconfig
    [deploy]
            config-file = /etc/git-deploy.conf

Then we configure git-deploy in the F</etc/git-deploy.conf> to roll
out two repositories, F</repo/code> and F</repo/static_assets>:

    $ cat /etc/git-deploy.conf
    ;; Global options
    [deploy]
            ;; Force users to have this umask
            restrict-umask = 0002

            ;; If this file exists all rollouts are blocked
            block-file = /etc/ROLLOUTS_BLOCKED

            ;; E-Mail addresses to complain to when stuff goes wrong
            support-email = [email protected], [email protected]

            ;; What strategy should we use to detect the repo name?
            repo-name-detection = dot-git-parent-dir

            ;; Where should the mail configured below go?
            announce-mail = [email protected]

            ;; When should we send an E-Mail?
            send-mail-on-sync   = true
            send-mail-on-revert = true

            ;; Where to store the timing information
            log-directory = /var/log/deploy

            ;; We want timing information
            log-timing-data = true

    ;; Per-repo options, keys here override equivalent keys in the
    ;; global options

    [deploy "repository code"]
            ;; Prefix to give to tags created here. A prefix of 'debug'
            ;; will result in debug-YYYYMMDD-HHMMSS tags
            tag-prefix = app

            ;; In code.git we put the .deploy file in lib/.deploy. this is
            ;; because traditionally we only sync out the lib
            ;; folder.
            deploy-file = lib/.deploy

            ;; Where the git-deploy hooks live
            hook-dir = /repos/hooks/git-deploy-data/deploy-code

    [deploy "repository static_assets"]
            ;; Prefix to give to tags created here. A prefix of 'debug'
            ;; will result in debug-YYYYMMDD-HHMMSS tags
            tag-prefix = app_tmpl

            ;; We sync out this whole repository
            deploy-file = .deploy

            ;; Where the git-deploy hooks live
            hook-dir = /repos/hooks/git-deploy-data/deploy-static_assets

Notice how they have sections of their own later in the config file,
these sections only apply to them using the
C<deploy.repo-name-detection> logic, any values in the per-repo
sections override the corresponding deploy.* values.

Since we're using the C<dot-git-parent-dir> strategy for
C<deploy.repo-name-detection> running git-deploy inside F</repo/code>
will cause us to pick up the "repository code" section of the
configuration. I.e. we're using the name of the parent folder of our
F<.git> directory.

=head1 WRITING DEPLOY HOOKS

The pre-deploy framework is expected to reside in the
F<$GIT_WORK_DIR/deploy> directory (i.e. the F<deploy> directory of the
repository that's being rolled out). This directory has the following
tree:

    $GIT_WORK_DIR/deploy/                   # deploy directory
                        /apps/              # Directory per application + 'common'
                             /common/       # deploy scripts that apply to all apps
                             /$app/         # deploy scripts for a specific $app
                        /sync/              # sync
                             /$app.sync

The C<$app> in F<deploy/{apps,sync}/$app> is the server prefix that
you'd see in the rollout tag. E.g. A company might have multiple environments
which they roll out, for instance "sheep", "cows" and "goats". Here is a practical
example of the deployment hooks that might be used in the C<sheep> environment:

    $ tree deploy/apps/{sheep,common}/ deploy/sync/
    deploy/apps/sheep/
    |-- post-pull.010_httpd_configtest.sh
    |-- post-pull.020_restart_httpd.sh
    |-- pre-pull.010_nobranch_rollout.sh
    |-- pre-pull.020_check_that_we_are_in_the_load_balancer.pl
    |-- pre-pull.021_take_us_out_of_the_load_balancer.pl
    `-- pre-pull.022_check_that_we_are_not_in_the_load_balancer.pl -> pre-pull.020_check_that_we_are_in_the_load_balancer.pl
    deploy/apps/common/
    |-- pre-sync.001_setup_affiliate_symlink.pl
    `-- pre-sync.002_check_permissions.pl
    deploy/sync/
    |-- sheep.sync

All the hooks in F<deploy/apps> are prefixed by a C<phase> in which
C<git-deploy> will execute them (e.g. C<pre-pull> just before a
pull).

During these phases C<git-deploy> will C<glob> in all the
F<deploy/apps/{common,$app}/$phase.*> hooks and execute them in
C<sort> order, first the C<common> hooks and then the C<$app> specific
hooks. Note that the hooks B<MUST> have their executable bit set.

=head2 Environment variables available to hooks

The following environment variables are available to the phase hooks:

=head3 GIT_DEPLOY_ACTION

The current action we're running, e.g. "start", "hotfix", "abort" etc.

=head3 GIT_DEPLOY_PHASE

The current hook phase, e.g. "post-pull", "pre-sync" etc.

=head3 GIT_DEPLOY_PREFIX

The prefix of the current environment, e.g. "sheep", "cron" etc.

=head3 GIT_DEPLOY_HOOK_PREFIX

The prefix of the currently executing hook, like L</GIT_DEPLOY_PREFIX>
except this will be "common" when the "common" hooks are being
executed.

=head3 GIT_DEPLOY_START_TAG

Set to the tag we started with, currently only set (and can only ever
be set) for a subset of the hooks.

=head3 GIT_DEPLOY_ROLLOUT_TAG

The tag we're rolling out, like L</GIT_DEPLOY_START_TAG> this isn't
set for all hooks.

=head2 Available phase hooks

Currently, these are the hooks that will be executed. All the
hooks, except the L</post-tree-update> hook, correspond to specific
git-deploy actions:

=head3 pre-start

The first hook to be executed. Will be run before the deployment tag
is created (but obviously, after we do C<git fetch>).

=head3 post-start

Executed after the start phase (also executed on hotfix), useful to
e.g. print out any custom messages you'd like to print out at the end
of the start/hotfix phase.

=head3 pre-pull

Executed before we update the working tree with C<git pull>. This is
where hooks that e.g. take the deployment machine out of the load
balancer should be executed.

=head3 post-pull

Just after the pull in the "start" phase.

=head3 pre-sync

Just before we create the tag we're about to sync out and execute the
F<deploy/sync/$app.sync> hook.

=head3 post-sync

After we've synced. Here you could e.g. send custom e-mails indicating
that the deployment was a success.

=head3 post-abort

Hooks executed after an C<abort>.

=head3 post-reset

Hooks executed after a reset, either via C<abort> or
C<revert>. Most of the time you want to use C<post-tree-update> hooks
instead, but this is useful e.g. for putting a staging server back
into a load balancer.

=head3 post-tree-update

Executed after we update the working tree to a new revision, whether
that's after the C<pull> in the C<start> phase, after C<git reset
--hard> in the C<abort> phase, or after a C<revert>.

Here's where hooks that e.g. restart the webserver and run any
critical tests (e.g. config tests) should be run.

The exit code from these hooks is ignored in actions like C<abort>
and C<revert>. We don't want the abort or revert to fail just
because a web server didn't restart.

=head3 log

Called at various points with log messages, these are just like normal
phase hooks except they'll have a few extra environment variables set
for them. By default we ignore the exit code of log hooks, because we
don't want failure in logging to stop the deployment.

=over

=item GIT_DEPLOY_LOG_LEVEL

The log level, the lowercase equivalent of the levels documented in
L<syslog(3)> without the C<LOG_*> prefix, e.g. "info" or "warning".

=item GIT_DEPLOY_LOG_MESSAGE

A free-form log message that we're passing to the log hook

=item GIT_DEPLOY_LOG_ANNOUNCE

Whether this message should be announced. These are messages that are
more important than others that you'd e.g. like to output to your IRC
or Jabber deployment channel.

=back

=head2 Return values

Each script is expected to return a nonzero exit code on failure, and
a zero exit code on success (in other words, standard Unix shell return
semantics). Any script that "fails" will cause C<git-deploy> to
abort at that point.

More granular failure codes are planned in the future. E.g. "failed
but should try again", "failed but should ask the user before trying
again" etc. But this hasn't yet been implemented.

=head2 Sync Hooks

A special case for a hook that really should be just a regular L<phase
hook|/Available phase hooks>. But isn't yet because it would have
required more major surgery on C<git-deploy> at the time phase
hooks were written, as well as access by the author to all deployment
environments (which wasn't the case).

The only notable difference is that there is only one phase hook for
each C<$app>, and it's located in F<deploy-$repo/sync/$app.sync>.

Note: the sync hook can be skipped (and the associated finish) with the
manual-sync action. This will however execute the pre-sync and post-sync
hooks, possibly with errors.

=cut

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