Using Symlinks for a Zero-downtime Deployment

We'll see a Capistrano-style deployment strategy, which employs symlinks to swap out old code for new code when we deploy.

We'll update our Fabfile to automate the same deployment process we saw in the last video.

Updated Fabfile

We dive right in and edit a complete fabfile.py. The video covers the details of it, but this is it!

from __future__ import with_statement
from time import time

from fabric.api import local, env, run, cd, get
from fabric.decorators import task
from fabric.contrib.files import exists

env.use_ssh_config = True
env.hosts = ['serial-app']
# env.hosts = ['45.55.209.211']
# env.user = 'serial'
# env.key_filename = '~/.ssh/id_series'

git_repo        = 'git@github.com:Servers-for-Hackers/serialapp.git'
git_branch      = 'master'
release_dir     = '/home/serial/serialapp.com/releases'
current_release = '/home/serial/serialapp.com/current'
repo_dir        = '/home/serial/serialapp.com/repo'
persist_dir     = '/home/serial/serialapp.com/persist'
next_release    = "%(time).0f" % {'time': time()}

@task
def deploy():
    init()
    update_git()
    create_release()
    build_site()
    swap_symlinks()

def init():
    if not exists(release_dir):
        run("mkdir -p %s" % release_dir)

    if not exists(repo_dir):
        run("git clone -b %s %s %s" % (git_branch, git_repo, repo_dir))

    if not exists("%s/storage" % persist_dir):
        run("mkdir -p %s/storage" % persist_dir)
        run("mkdir -p %s/storage/app" % persist_dir)
        run("mkdir -p %s/storage/framework" % persist_dir)
        run("mkdir -p %s/storage/framework/cache" % persist_dir)
        run("mkdir -p %s/storage/framework/session" % persist_dir)
        run("mkdir -p %s/storage/framework/views" % persist_dir)
        run("mkdir -p %s/storage/logs" % persist_dir)

def update_git():
    with cd(repo_dir):
        run("git checkout %s" % git_branch)
        run("git pull origin %s" % git_branch)

def create_release():
    release_into = "%s/%s" % (release_dir, next_release)
    run("mkdir -p %s" % release_into)
    with cd(repo_dir):
        run("git archive --worktree-attributes %s | tar -x -C %s" % (git_branch, release_into))

def build_site():
    with cd("%s/%s" % (release_dir, next_release)):
        run("composer install")

def swap_symlinks():
    # Build release directory
    release_into = "%s/%s" % (release_dir, next_release)

    # Symlink new .env and existing storage
    run("ln -nfs %s/.env %s/.env" % (persist_dir, release_into))
    run("rm -rf %s/storage" % release_into)
    run("ln -nfs %s/storage %s/storage" % (persist_dir, release_into))

    # Put site live
    run("ln -nfs %s %s" % (release_into, current_release))

    # Reload PHP-FPM gracefully
    run('sudo service php5-fpm reload')

Once this is updated, we can run the deploy task.

# On local computer

## Go to serialapp code in local development
cd ~/Sites/serialapp

## Source the virtualenv with fabric
## if needed
source .venv/bin/activate

## List tasks available
fabric -l

## Run our "deploy" task
fabric deploy