Jekyll build-on-Heroku-deploy can leverage on Rails asset pipeline rake assets:precompile hook to avoid relying on a custom buildpack, please check Jesse B. Hannah method here: https://github.com/jbhannah/jbhannah.net/commit/c7a22cfa62b1274342e4e162125b3ae171c3b125
Heroku Ruby Jekyll Buildpack is an up-to-date fork of Heroku's official Ruby buildpack (v85) with added support for generating static Jekyll sites during the build/deployment stage.
With this buildpack you no longer need pre-build the site or commit the _site build directory to your repo. This simplifies the deployment process and keeps the repo clean. All of the standard Ruby tools are maintained in this buildpack, so you can take full advantage of Rack middleware and other useful tools from the Ruby ecosystem.
heroku create --buildpack http://github.com/jeremyvdw/heroku-buildpack-ruby-jekyll.git
or add this buildpack to your current app
heroku config:add BUILDPACK_URL=http://github.com/jeremyvdw/heroku-buildpack-ruby-jekyll.git
Create a Ruby web app with dependencies managed by Bundler and a Jekyll site. Heroku-Jekyll-Hello-World can be used as a sample starter.
Push to heroku
git push heroku master
Watch it "Building jekyll site"
-----> Fetching custom git buildpack... done
-----> Ruby app detected
-----> Compiling Ruby/Rack
-----> Using Ruby version: ruby-2.1.0-rbx-2.2.1
-----> Installing dependencies using Bundler version 1.3.2
Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin --deployment
Using RedCloth (4.2.9)
Using blankslate (2.1.2.4)
Using fast-stemmer (1.0.2)
Using classifier (1.3.3)
Using colorator (0.1)
Using highline (1.6.20)
Using commander (4.1.5)
Using ffi (1.9.3)
Using ffi2-generators (0.1.1)
Using liquid (2.5.4)
Using rb-fsevent (0.9.3)
Using rb-inotify (0.9.2)
Using rb-kqueue (0.2.0)
Using listen (1.3.1)
Using maruku (0.7.0)
Using posix-spawn (0.3.8)
Using yajl-ruby (1.1.0)
Using pygments.rb (0.5.4)
Using redcarpet (2.3.0)
Using safe_yaml (0.9.7)
Using parslet (1.5.0)
Using toml (0.1.0)
Using jekyll (1.4.0)
Using psych (2.0.2)
Using rack (1.5.2)
Using puma (2.7.1)
Using rack-jekyll (0.4.1)
Using rubysl-abbrev (2.0.4)
Using rubysl-base64 (2.0.0)
Using rubysl-benchmark (2.0.1)
Using rubysl-bigdecimal (2.0.2)
Using rubysl-cgi (2.0.1)
Using rubysl-cgi-session (2.0.1)
Using rubysl-cmath (2.0.0)
Using rubysl-complex (2.0.0)
Using rubysl-continuation (2.0.0)
Using rubysl-coverage (2.0.3)
Using rubysl-english (2.0.0)
Using rubysl-csv (2.0.2)
Using rubysl-curses (2.0.0)
Using rubysl-date (2.0.6)
Using rubysl-delegate (2.0.1)
Using rubysl-digest (2.0.3)
Using rubysl-drb (2.0.1)
Using rubysl-e2mmap (2.0.0)
Using rubysl-enumerator (2.0.0)
Using rubysl-erb (2.0.1)
Using rubysl-etc (2.0.3)
Using rubysl-expect (2.0.0)
Using rubysl-fcntl (2.0.4)
Using rubysl-fiber (2.0.0)
Using rubysl-fileutils (2.0.3)
Using rubysl-find (2.0.1)
Using rubysl-forwardable (2.0.1)
Using rubysl-getoptlong (2.0.0)
Using rubysl-socket (2.0.1)
Using rubysl-thread (2.0.2)
Using rubysl-gserver (2.0.0)
Using rubysl-io-console (2.0.0)
Using rubysl-io-nonblock (2.0.0)
Using rubysl-io-wait (2.0.0)
Using rubysl-ipaddr (2.0.0)
Using rubysl-mathn (2.0.0)
Using rubysl-readline (2.0.2)
Using rubysl-irb (2.0.4)
Using rubysl-logger (2.0.0)
Using rubysl-matrix (2.1.0)
Using rubysl-shellwords (2.0.0)
Using rubysl-mkmf (2.0.1)
Using rubysl-monitor (2.0.0)
Using rubysl-mutex_m (2.0.0)
Using rubysl-net-ftp (2.0.1)
Using rubysl-singleton (2.0.0)
Using rubysl-net-http (2.0.4)
Using rubysl-net-imap (2.0.1)
Using rubysl-net-pop (2.0.1)
Using rubysl-net-protocol (2.0.1)
Using rubysl-net-smtp (2.0.1)
Using rubysl-net-telnet (2.0.0)
Using rubysl-nkf (2.0.1)
Using rubysl-observer (2.0.0)
Using rubysl-open-uri (2.0.0)
Using rubysl-open3 (2.0.0)
Using rubysl-openssl (2.0.5)
Using rubysl-optparse (2.0.1)
Using rubysl-ostruct (2.0.4)
Using rubysl-pathname (2.0.0)
Using rubysl-prettyprint (2.0.2)
Using rubysl-prime (2.0.0)
Using rubysl-profile (2.0.0)
Using rubysl-profiler (2.0.1)
Using rubysl-pstore (2.0.0)
Using rubysl-pty (2.0.2)
Using rubysl-rational (2.0.1)
Using rubysl-resolv (2.0.0)
Using rubysl-rexml (2.0.2)
Using rubysl-rinda (2.0.0)
Using rubysl-rss (2.0.0)
Using rubysl-scanf (2.0.0)
Using rubysl-securerandom (2.0.0)
Using rubysl-set (2.0.1)
Using rubysl-stringio (2.0.0)
Using rubysl-strscan (2.0.0)
Using rubysl-sync (2.0.0)
Using rubysl-syslog (2.0.1)
Using rubysl-tempfile (2.0.1)
Using rubysl-thwait (2.0.0)
Using rubysl-time (2.0.3)
Using rubysl-timeout (2.0.0)
Using rubysl-tmpdir (2.0.0)
Using rubysl-tsort (2.0.1)
Using rubysl-un (2.0.0)
Using rubysl-uri (2.0.0)
Using rubysl-weakref (2.0.0)
Using rubysl-webrick (2.0.0)
Using rubysl-xmlrpc (2.0.0)
Using rubysl-yaml (2.0.4)
Using rubysl-zlib (2.0.1)
Using rubysl (2.0.15)
Using rubysl-json (2.0.2)
Using bundler (1.3.2)
Your bundle is complete! It was installed into ./vendor/bundle
Bundle completed (5.85s)
Cleaning up the bundler cache.
-----> Writing config/database.yml to read from DATABASE_URL
Building jekyll site
Configuration file: /tmp/build_47908e9f-b52c-44f9-8397-d9e6beae90ee/_config.yml
Source: /tmp/build_47908e9f-b52c-44f9-8397-d9e6beae90ee
Destination: /tmp/build_47908e9f-b52c-44f9-8397-d9e6beae90ee/_site
Generating... done.
-----> Discovering process types
Procfile declares types -> web
Default types for Ruby -> console, rake
-----> Compiled slug size: 107.0MB
-----> Launching... done, v7
http://XXXXXX.herokuapp.com deployed to Heroku
The blog post introducing this buildpack: http://mwmanning.com/2011/11/29/Run-Your-Jekyll-Site-On-Heroku.html.