5. CouchDB and Domain-Driven Design

This post covered two topics that are of great interest to me. Document databases like CouchDB have much potential when it comes to domain-driven design. The post outlined some techniques for serializing domain objects into CouchDB documents.

4. Addressing the NoSQL Criticism

I heard a lot of NoSQL bashing this year at OSCON. As a result, I decided to write a rebuttal to many of the criticisms that I heard. This post inspired a lively comment thread.

3. Testing PHP 5.4

This was a short post on how to help the PHP Quality Assurance Team by running the tests for the latest development version of PHP 5.4. It covered downloading, compiling, and running the tests. Most importantly, it also covered reporting your test results.

2. Exploring RabbitMQ and PHP

I was exploring the possibility of using RabbitMQ for an upcoming project. I decided to post some notes on my experience getting started with RabbitMQ and integrating it with PHP. I haven’t ended up using RabbitMQ in production yet, but I’m confident that I’ll end up using it at some point.

1. CouchDB jQuery Plugin Reference

I had been frustrated by the lack of documentation for the CouchDB jQuery plugin—so decided to write my own. After I wrote the blog post, Max Ogden pointed me to Dale Harvey‘s documentation generator for jquery.couch.js and a copy of the generated jQuery CouchDB documentation. Max and Dale are also working on a more flexible jquery.couch2.js.

• Core PHP
• Web Development
• Training
• User Experience (UX)

Boston PHP will be hosting the event in partnership with other northeast regional user groups including the Burlington, Vermont PHP Users Group (which I organize) and the Atlantic Canadian PHP User Group. We’re still early in the planning stages, so there will be more details to come later. If you’re interested in speaking, have ideas for the event, or are interested in sponsoring then please send a message to Boston PHP.

I. Codebase

“One codebase tracked in revision control, many deploys”

There’s really not much here that would be different in PHP versus any other language. Who isn’t using some form of revision control these days?

II. Dependencies

“Explicitly declare and isolate dependencies”

There are a few tools available to PHP developers to help manage dependencies. The PEAR package manager may help here, but has its flaws. Pyrus, the PEAR2 package manager, looks promising. There’s also Composer. I’ve heard of people using their operating system’s package manager (e.g. RPM) to deploy their PHP applications and manage dependencies. I’m not sure if there any tools in PHP to enforce dependency isolation.

III. Config

“Store config in the environment”

The simplest option here is to use environment variables. Many frameworks, including Zend Framework, allow you to have environment-specific configuration such as development, test, and production. This is not recommended for twelve-factor apps as it doesn’t scale as new environments are added.

IV. Backing Services

“Treat backing services as attached resources”

There’s not really anything to say here that’s specific to PHP.

V. Build, release, run

“Strictly separate build and run stages”

Phing or the more general-purpose Ant could work here. Even though it’s not written in PHP, there’s no reason why you couldn’t use Capistrano for this. I don’t think the run stage typically applies to PHP, as it happens implicitly as part of the release stage. However, there are tasks such as flushing the APC cache (if apc.stat=0) that might be considered part of the run stage.

VI. Processes

“Execute the app as one or more stateless processes”

PHP processes are already stateless and shared-nothing. This makes PHP a great fit for twelve-factor apps. Memory space or the filesystem should be used as a short-lived, single-process cache. If you’re using an asset manager, such as Assetic, then any assets should be compiled and cached during the build stage.

VII. Port binding

“Export services via port binding”

I don’t think port binding applies to PHP applications—at least not in the way it’s meant in twelve-factor. PHP relies on a web server and uses something like FastCGI or PHP-FPM to communicate with the web server. PHP 5.4 will have its own built-in web server, but this is intended for development use only. It’s really the combination of PHP and its web server that will be bound to a port. This brings up challenges when it comes to dependency management, as the web server itself is now a dependency.

VIII. Concurrency

“Scale out via the process model”

I’m not sure how processes would become first-class citizens in a PHP web application. However, each individual request/response cycle is handled by its own process. In that regard, PHP already uses the process model.

IX. Disposability

“Maximize robustness with fast startup and graceful shutdown”

PHP processes are very disposable. Again, this is just part of how PHP works.

X. Dev/prod parity

“Keep development, staging, and production as similar as possible”

Nothing specific to PHP here. Although, it’s not uncommon for PHP developers to use SQLite in development and MySQL or PostgreSQL in production. This is not recommended for a twelve-factor app—use the same software and versions of backing services in all environments.

XI. Logs

“Treat logs as event streams”

There are tons of logging options in PHP. Zend_Log_Writer_Stream lets you send log data to a PHP stream. Alternatively, StatsD and the PHP StatsD library look pretty good.

XII. Admin processes

“Run admin/management tasks as one-off processes”

This is easy enough in PHP. If you want an interactive shell with readline history, tab completion, and quick access to documentation then check out phpsh.

Zend Framework 2.0 should be released soon, and it has been four years since the last major release (1.0). This is not to imply that Zend Framework has been stagnant—far from it. There has been a ton of development effort and many improvements to Zend Framework since 1.0. I have a great amount of trust in the team, and I have complete confidence that Zend Framework 2.0 will be an awesome framework. This post is intended to make the case for rapid release cycles for software in general, and is not meant to be a criticism of Zend Framework or the development processes behind it. However, the discussions around Zend Framework’s release cycle are what’s prompting me to make this post.

First, let me describe what I mean by a “rapid release cycle”. In this context, I mean rapid releases of major versions. Put simply, major versions are those that allow backwards compatible breaks. This is somewhat controversial. I don’t think anyone really has any big concerns with the rapid release of minor (introduction of new features while maintaining backwards compatibility) or maintenance (bug and/or security fix) releases. “Rapid” depends on the context. Both Chrome and Firefox have adopted a six-week release cycle. As I mentioned before, six months could be considered “rapid” for a framework.

For a framework (and maybe for other software), I think the following rules are necessary in order for a rapid release cycle to work:

• Minimize backwards compatibility changes between major releases. Targeted and strategic refactoring, rather than major overhauls, are preferable if you are releasing often. Small backwards compatibility changes makes migrating from one major version to another much easier.
• Mark some major releases as “Long Term Support” (LTS) releases. Provide bug fix updates and security patches to these releases for three to five years. This provides a “safe” option to those who value stability and don’t want to upgrade very often. In the context of Zend Framework, it is obviously Zend’s decision if they want to take on this burden. If not, then I don’t think a rapid release cycle is viable.

What are the concerns with a rapid release cycle? I’ll paraphrase, and then address, the major concerns that I’ve heard.

“Rapid releases of major versions are just for psychological effect and has no affect on the delivery pace of new features.” This is both true and false. See my earlier post on iterative vs. incremental development. If development is incremental and driven entirely by a pre-determined roadmap then there is no tangible differences between a “normal” and a rapid release cycle. The development of many consumer software packages is perceived as incremental, in which case major version bumps are mostly psychological. However, if you take an iterative development approach and build-in outside learning from end-users into your process, then a rapid release cycle gives you the chance to change course based on outside feedback. Learning opportunities are introduced that you would have never had if your software wasn’t actually used by real people in the real world.

“Rapid release cycles are for consumer software where you don’t have to care for backward compatibility.” This is related to the previous concern. My response is that rapid release cycles are for any product where learning from real-world usage and outside input can be used to improve the product. To quote Steve Blank, “There are no answers inside the building.”

“It forces people to upgrade too often and rewrite their code, or get left behind.” See my earlier note about minimizing backwards compatibility changes in each major release. Additionally, it is much easier to automate upgrades if the backwards compatibility changes are small. There should be little code rewriting for applications built using the framework with each major version upgrade of the framework.

“Having lots of end-of-life (EOL) versions being used could be a security risk.” See my earlier note about providing LTS releases. Each major release should come with a pre-determined EOL date. It is the responsibility of the end-user (in the case of a framework, the developer) to be aware of a release’s EOL date. Using EOLed software is always a security risk.

While not specifically a concern with rapid release cycles, there’s a general mentality that major releases are “our chance to get it right.” Hopefully you’re a better software developer than you were even six months ago. Chances are you know more than you did then, and would approach solving problems differently now. Think six months before that, and six months before that. Now project this into the future. Where will you be in six months? Will you know more than you do now? Will you approach solving problems differently than you do now? If you’re a good software developer, you will never get it “right”—you will always be better six months from now than you are today and know more than you know today. A rapid release cycle allows you to apply new learning, knowledge, and perspective as often as possible. Do your best today, and give yourself opportunities to do your best in the future as well.

Personally, I’d like to encourage submissions on the following topics:

• More talks related to free/open source software (PHP, Ruby, Python, etc.)
• Arduino and/or other hardware programming
• Software development patterns and practices
• Web analytics and metrics
• Front-end web development (JavaScript, CSS, etc.)
• Node.js and other emerging technologies
• Mobile application development
• Anything you’re passionate about!

Propose a session or two now—you know you want to!

Aggregates are groupings of associated Entities and Value Objects. Within an Aggregate, one member is designated as the Aggregate Root. External references are limited to only the Aggregate Root. Aggregates should follow transaction, distribution, and concurrency boundaries. Guess what else is defined by transaction, distribution, and concurrency boundaries? That’s right, JSON documents in CouchDB.

Let’s take a look at an example Aggregate, that representing a blog entry and related metadata. Note that the following UML diagrams are for classes in PHP, but it should be easy enough to translate these examples to any object-oriented programming language. We’ll start with the Entry Entity, which will serve as our Aggregate Root:

-----------------------------------------
|                 Entry                 |
-----------------------------------------
|+ id : string                          |
|+ rev : string                         |
|+ title : Text                         |
|+ updated : Date                       |
|+ authors : Person[*]                  |
|+ content : Text                       |
-----------------------------------------
|+ __construct(entry : array) : void    |
|+ toArray() : array                    |
-----------------------------------------

The Text Value Object:

----------------------------------------------
|                    Text                    |
----------------------------------------------
|- type : string                             |
|- text : string                             |
----------------------------------------------
|+ __construct(type : string, text : string) |
|+ toArray() : array                         |
----------------------------------------------

The Date Value Object:

--------------------------------------
|                Date                |
--------------------------------------
|- timestamp : integer               |
--------------------------------------
|+ __construct(timestamp : integer)  |
|+ __toString() : string             |
--------------------------------------

The Person Value Object:

-------------------------------------------------------------
|                           Person                          |
-------------------------------------------------------------
|- name : string                                            |
|- uri : string                                             |
|- email : string                                           |
-------------------------------------------------------------
|+ __construct(name : string, uri : string, email : string) |
|+ toArray() : array                                        |
-------------------------------------------------------------

I recommend serializing each Aggregate, starting with the Aggregate Root, into a JSON document. Control access to Aggregate Roots through a Repository. The toArray() methods above return an associative array representation of each object. The Repository can then transform the array into JSON for storage in CouchDB. Let’s take a look at the EntryRepository:

---------------------------------
|        EntryRepository        |
---------------------------------
|                               |
---------------------------------
|+ get(id : string) : Entry     |
|+ post(entry : Entry) : void   |
|+ put(entry : Entry) : void    |
|+ delete(entry : Entry) : void |
---------------------------------

Here’s an example of what the Aggregate’s object graph might look like, serialized as a JSON document:

{
    "_id": "http://bradley-holt.com/?p=1251",
    "title": {
        "type": "text",
        "text": "CouchDB and Domain-Driven Design"
    },
    "updated": "2011-08-02T15:30:00+00:00",
    "authors": [
        {
             "name": "Bradley Holt",
             "uri": "http://bradley-holt.com/",
             "email": "bradley.holt@foundline.com"
        }
    ],
    "content": {
        "type": "html",
        "text": "<p>I've found CouchDB to be a great fit for…</p>"
    }
}

You can also provide access to CouchDB views through Repositories. In the above example, this could be through the addition of an index(skip : integer, limit : integer) : Entry[*] method to the the EntryRepository (note that this is a naive pagination implementation, especially on large data sets—but that’s beyond the scope of this blog post). For more complex views, you may want to create a separate Repository for each CouchDB view.

I’ll be using RabbitMQ first from PHP, but I plan on using it to send and receive messages to and from other systems. Following are the steps I used to get RabbitMQ and PHP’s AMQP library setup on my development machine.

First, I installed RabbitMQ using MacPorts:

$ sudo port install rabbitmq-server

Then, I started RabbitMQ:

$ sudo rabbitmq-server -detached

Next, I installed the librabbitmq library using a slight variation of the instructions on PHP’s AMQP Installation page (you may need to install Mercurial first):

$ hg clone http://hg.rabbitmq.com/rabbitmq-c/rev/3c549bb09c16 rabbitmq-c
$ cd rabbitmq-c
$ hg clone http://hg.rabbitmq.com/rabbitmq-codegen/rev/f8b34141e6cb codegen
$ autoreconf -i && ./configure && make && sudo make install

Then, I installed the AMQP extension using PECL:

$ sudo pecl install amqp-beta

To test that everything works, I opened up two interactive PHP shells using php -a. I ran the following code in the first PHP shell:

$exchangeName = 'messages';
$routeKey = 'routeA';
$message = 'Hello, world.';
$connection = new AMQPConnection();
$connection->connect();
$exchange = new AMQPExchange($connection);
$exchange->declare($exchangeName);

I then ran the following code in the second PHP shell:

$exchangeName = 'messages';
$routeKey = 'routeA';
$connection = new AMQPConnection();
$connection->connect();
$queue = new AMQPQueue($connection);
$queue->declare($exchangeName);
$queue->bind($exchangeName, $routeKey);

Back in the first PHP shell:

$exchange->publish($message, $routeKey);

Back in the second PHP shell:

$message = $queue->get();
print_r($message);

Here is the output I got from the print_r statement:

Array
(
    [routing_key] => routeA
    [exchange] => messages
    [delivery_tag] => 1
    [Content-type] => text/plain
    [count] => 0
    [msg] => Hello, world.
)

There are several other options that can be set, and a lot more to learn about RabbitMQ and AMP. Check out the documentation for PHP’s AMQP extension for details about working with AMQP servers from PHP.

First, make sure that you have subversion, autoconf, automake, gcc, bison, flex, and re2c installed. I’m using a Mac, so I was able to install most of these using MacPorts (Homebrew would have worked, too). Next, do a checkout of the PHP 5.4 branch:

$ svn co https://svn.php.net/repository/php/php-src/branches/PHP_5_4 php54

Then:

$ cd php54
$ ./buildconf
$ ./configure
$ make
$ make test

Both the make and make test steps may take awhile. Assuming you get some failed tests like I did, then you will see the following message and prompt:

You may have found a problem in PHP.
This report can be automatically sent to the PHP QA team at
http://qa.php.net/reports and http://news.php.net/php.qa.reports
This gives us a better understanding of PHP's behavior.
If you don't want to send the report immediately you can choose
option "s" to save it.    You can then email it to qa-reports@lists.php.net later.
Do you want to send this report now? [Yns]:

I opted to send the report now, so entered Y. Next, I was prompted for my email address:

Please enter your email address.
(Your address will be mangled so that it will not go out on any
mailinglist in plain text):

I entered my email address and then:

Posting to http://qa.php.net/buildtest-process.php

Thank you for helping to make PHP better.

Pretty straightforward. At this point, your report should be aggregated on the PHP Test Reports Summary page. If you want to run more tests, then configure as many extensions as possible during the configure step. Take a look at the shell script in Rasmus’ instructions for details. If you’d like, you can examine the failed tests and see if you can come up with a patch to fix the problem. Again, see Rasmus’ instructions for details.

CouchDB is a document-oriented database that uses JSON documents, has a RESTful HTTP API, and is queried using map/reduce views. Each of these properties alone, especially MapReduce views, may seem foreign to developers more familiar with relational databases. This tutorial will teach web developers the concepts they need to get started using CouchDB in their projects. Several CouchDB libraries are available for PHP and we will take a look at the more popular ones.

This will be the 7th annual ZendCon and will take place October 17-20, 2011 in Santa Clara, California. Registration is open—hope to see you there!

We’re a new startup with some venture backing. We’re looking to add an experienced developer to help us out for the next five weeks (and possibly more). Qualifications are:

• experienced PHP hacker (5+ years)
• full understanding of MVC frameworks (codeignitor, cake, symfony, zend, kohana or the like)
• comfortable with the LAMP stack
• understanding of git
• able to plug into a new project and start coding in under a day

You’ll be working with a team of 6 developers in downtown Burlington.

Kohort was featured in TechCrunch the other day for raising a “seed” round of $3 million. If you’re interested, contact Steve Blood. You can find Steve’s email address in this thread, or let me know and I can put you in touch with him.