Rails%203%20In%20Action

402 CHAPTER 14 Deployment
executing locally: "git ls-remote [git_path] HEAD"
* executing "git clone -q [git_path] [release_path] &&
cd [release_path] &&
git checkout -q -b deploy [SHA1 hash] &&
(echo [SHA1 hash] > [release_path]/REVISION)"
servers: ["your-server"]
This task first runs git ls-remote, a lesser-known Git command, locally (not on the
server), which will get the current SHA for HEAD, the latest commit to the master
branch, unless you set a branch in Capistrano’s configuration.
The next thing Capistrano does is put the current revision in a file called
REVISION. If you like, you can alter the layout of your application to read the value
from this file and put it in your application’s layout as a HTML comment so that when
you do a deploy to the server, you can check this hash to see if it is the latest code.
The next couple of lines output from cap deploy are from the beginning of the
deploy:finalize_update task:
* executing "chmod -R g+w [release_path]"
servers: ["localhost"]
[localhost] executing command
command finished
With this chmod command, Capistrano ensures that your new release’s directory is
group writable (g+w), allowing the user/group to make any modifications to this
directory they like, barring all others.
Finally, the deploy:finalize_update then removes the log, public/system, and
tmp/pids directories and symbolically links the shared/log, shared/system, and
shared/pids directories (in your application’s deployed path) to these paths respectively.
It does that in this little series of commands:
* executing "rm -rf [release_path]/log
[release_path]/public/system
[release_path]/tmp/pids &&
mkdir -p [release_path]/public &&
mkdir -p [release_path]/tmp &&
ln -s [shared_path]/log [release_path]/log &&
ln -s [shared_path]/system [release_path]/public/system &&
ln -s [shared_path]/pids [release_path]/tmp/pids
servers: ["your-server"]
[your-server] executing command
command finished
Next, Capistrano will use the find command to touch every file in the public/images,
public/stylesheets, and public/javascripts to update their last modified time. This is so
that when a user visits your site they get the latest image, stylesheet, or JavaScript file
rather than a cached file. It does this with this part of the output:
* executing "find [release_path]/public/images
[release_path]/public/stylesheets
[release_path]/public/javascripts
-exec touch -t [timestamp] {} ';'; true"