Update Mar 28, 2016: It is no longer necessary (and hence discouraged) to fork the buildpack and rebuild it completely. The official PHP buildpack now has support for so-called custom platform repositories, and I’ve built one for V8Js meanwhile.

The other day I’ve configured a Dokku instance on my root server and then tried to install a PHP project requiring the V8Js extension. This of course failed for obvious reasons: Heroku’s buildpack for PHP doesn’t provide the V8Js PHP extension.

Luckily the buildpack is available on Github. So it should be possible to have a fork that supports V8Js.

So here we go, how hard can it be? :)

If you’re just interested in using the buildpack I’ve created, feel free to just use my own fork on Github. The master branch references my personal S3 bucket, so Heroku or Dokku just fetch the needed resources from there.

Below you’ll find a step by step guide on how to build such a buildpack on your own:

Step 0: Setting up S3 bucket

The buildpack assumes that the binaries are stored on S3; hence a new S3 bucket (along an IAM user with access on that bucket) needs to be created first.

Step 1: Clone Heroku’s PHP buildpack

First step is to fetch Heroku’s original build pack to a local workspace:

$ git clone https://github.com/heroku/heroku-buildpack-php
$ cd heroku-buildpack-php

Step 2: Create app on Dokku and configure remote

… before any modification, just create an app as a clean base for building the binaries later on:

$ dokku apps:create buildpack-php
$ dokku config:set buildpack-php BUILDPACK_URL="https://github.com/heroku/heroku-buildpack-python"
$ git remote add dokku ssh://dokku@dokku.brokenpipe.de:20022/buildpack-php

Step 3: Configure app

S3/IAM access key + secret need to be provided as environment variables, therefore we simply set them with dokku config:set.

$ dokku ps:scale buildpack-php web=0
$ dokku config:set buildpack-php AWS_ACCESS_KEY_ID="XXXXXXXXXXXXXXXXXXXX"
$ dokku config:set buildpack-php S3_BUCKET="buildpack-phpv8"
$ dokku config:set buildpack-php S3_PREFIX="dist-cedar-14-master"
$ dokku config:set buildpack-php STACK="cedar-14"
$ dokku config:set buildpack-php WORKSPACE_DIR=/app/support/build

Step 4: Upload the buildpack to Dokku

If the app is configured as needed, just push the unmodified code to see of everything works as expected:

$ git push dokku master

Step 5: Build used libraries

Evey build should have its own dokku run to ensure that nothing else but the declared dependencies can be used plus the packages are as clean as possible:

$ dokku run buildpack-php bob deploy libraries/gettext
$ dokku run buildpack-php bob deploy libraries/icu
$ dokku run buildpack-php bob deploy libraries/libmcrypt
$ dokku run buildpack-php bob deploy libraries/pcre
$ dokku run buildpack-php bob deploy libraries/zlib

Step 6: Build Apache, Nginx & PHP

$ dokku run buildpack-php bob deploy apache-2.4.16
$ dokku run buildpack-php bob deploy nginx-1.8.0
$ dokku run buildpack-php bob deploy php-min
$ dokku run buildpack-php bob deploy composer
$ dokku run buildpack-php bob deploy composer-1.0.0alpha11

The php-min package is always initially installed on every built slug (container) and used to track dependencies & installation candidates. The composer installer needs information on which PHP versions & extensions are available, which are made available by means of JSON manifests, which need to be uploaded seperately.

u26678@1b8458e5519f:~$ bob build php-5.5.30

Fetching dependencies... found 4:
  - libraries/zlib
  - libraries/libmcrypt
  - libraries/icu
  - libraries/gettext
Building formula php-5.5.30 in /tmp/bobE7yqsM:
    -----> Building PHP 5.5.30...
    -----> Done. Run 's3cmd --ssl --access_key=$AWS_ACCESS_KEY_ID --secret_key=$AWS_SECRET_ACCESS_KEY --acl-public put /tmp/bobE7yqsM/php-5.5.30.composer.json s3://buildpack-phpv8/dist-cedar-14-master/php-5.5.30.composer.json' to upload manifest.
u26678@1b8458e5519f:~$ s3cmd --ssl --access_key=$AWS_ACCESS_KEY_ID --secret_key=$AWS_SECRET_ACCESS_KEY --acl-public put /tmp/bobE7yqsM/php-5.5.30.composer.json s3://buildpack-phpv8/dist-cedar-14-master/php-5.5.30.composer.json
'/tmp/bobE7yqsM/php-5.5.30.composer.json' -> 's3://buildpack-phpv8/dist-cedar-14-master/php-5.5.30.composer.json'  [1 of 1]
 2026 of 2026   100% in    0s     3.96 kB/s  done
'/tmp/bobE7yqsM/php-5.5.30.composer.json' -> 's3://buildpack-phpv8/dist-cedar-14-master/php-5.5.30.composer.json'  [1 of 1]
 2026 of 2026   100% in    0s     3.53 kB/s  done
Public URL of the object is: http://buildpack-phpv8.s3.amazonaws.com/dist-cedar-14-master/php-5.5.30.composer.json

… the build deploy command automatically creates the manifest and prints the command required to publish it. Copy & paste FTW :-)

… repeat that for php-5.6.16 and php-7.0.1

Last but not least all of those little manifests files need to be collected into a single file named packages.json:

u4725@983895293e5e:~$ support/mkrepo.sh
-----> Fetching manifests...
WARNING: Empty object name on S3 found, ignoring.
's3://buildpack-phpv8/dist-cedar-14-master/ext-v8js-0.4.0_php-5.5.composer.json' -> './ext-v8js-0.4.0_php-5.5.composer.json'  [1 of 7]
 393 of 393   100% in    0s     2.74 kB/s  done
's3://buildpack-phpv8/dist-cedar-14-master/ext-v8js-0.4.0_php-5.6.composer.json' -> './ext-v8js-0.4.0_php-5.6.composer.json'  [2 of 7]
 393 of 393   100% in    0s     3.31 kB/s  done
-----> Generating packages.json...
-----> Done. Run 's3cmd --ssl --access_key=$AWS_ACCESS_KEY_ID --secret_key=$AWS_SECRET_ACCESS_KEY --acl-public put packages.json s3://buildpack-phpv8/dist-cedar-14-master/packages.json' to upload repository.
u4725@983895293e5e:~$ s3cmd --ssl --access_key=$AWS_ACCESS_KEY_ID --secret_key=$AWS_SECRET_ACCESS_KEY --acl-public put packages.json s3://buildpack-phpv8/dist-cedar-14-master/packages.json
'packages.json' -> 's3://buildpack-phpv8/dist-cedar-14-master/packages.json'  [1 of 1]
 9913 of 9913   100% in    0s    19.31 kB/s  done
'packages.json' -> 's3://buildpack-phpv8/dist-cedar-14-master/packages.json'  [1 of 1]
 9913 of 9913   100% in    0s    17.36 kB/s  done
Public URL of the object is: http://buildpack-phpv8.s3.amazonaws.com/dist-cedar-14-master/packages.json

… again, mkrepo.sh tells us how to upload the resulting file.

… now we have a buildpack for PHP that is functionally equivalent to Heroku’s version (apart from not having compiled each and every PHP version and extension, that might be available on Heroku).

Step 7: Update bin/compile

bin/compile is the shell script that is executed during the git push to either Dokku or Heroku; it has a variable named S3_URL which needs to point to the S3 bucket created in Step 0.

Step 8: Adding own recipes

As the buildpack clone is usable, now it’s time to add further recipies. In case of V8Js this is the V8 library itself (packages as libraries/v8) and the extension plus a bare version for every major PHP release.

The bare version is the extension alone, without the PHP version included, that it was built against as well as any further dependencies (V8 in that case). The non-bare variant ships all dependencies except for PHP itself.

The recipes themselves are simple shell scripts.

The V8 library as well as the bare package versions don’t need a manifest file, as they are just needed during build time. The extension package itself needs one however, otherwise composer won’t find it … and hence cannot install it. This is in case of the v8js package the manifest file must be uploaded manually + the packages.json file needs to be regenerated.