With the launch of landfill.amo[1] we bypass the entire headache. The site started with a clean database and I uploaded an add-on to show it worked, but otherwise it’s empty. It’s compact, fast, and simple to use. The beauty of the site for volunteers and casual developers is that the database and the filesystem are available in their entirety to download. This means you can check out the code, fill in the configuration, import the landfill database and have the site 90% running.[2]

Perhaps a testament to the obscene number of open bugs for AMO right now, but this also solves a second long standing problem where localizers couldn’t see the entire site. On landfill, anyone can be an administrator, an editor, or any other permission level they’d like; and they’ll be able to see the entire site.

If you’ve been overwhelmed or frustrated trying to set up AMO in the past, now is a good time to give it another shot. The landfill should just get better with age and use – if a few people register and add some data the available database dumps will get richer.

If there is a part of the site that isn’t working and you need it to be, let me know. Keep in mind this is only the new Python code, so the few parts that are still on PHP (like the admin panel) won’t be available until they are ported. Code is updated near-instantly on commit, localization changes are updated every 5 minutes.

[1] Forgive the fake certificate. This is a sandbox for developers, y’all know what you’re doing.

[2] Honestly, 90% is really all you need. We do a lot of stuff for scalability, statistics, etc. and unless you’re actually working on that part of the site, you don’t need those elements running. Of course, you’re more than welcome to turn them on, I’m just trying to make it easy.

In January of 2010 we started migrating addons.mozilla.org from CakePHP to Django. It was a controversial decision. Developers were ambivalent to excited, managers were opposed to neutral – a split anyone would expect. When I first talked about it I expected to be able to turn off PHP by the end of the year. It didn’t turn out quite like that.

Fifteen months later we’re still transitioning and it’s still stressful. The toughest part about a major migration like this is that there is only one team that is doing the migration, continuing to add the new features we need, and all the while maintaining the old site. That’s a stressful environment for developers since the interactions between the languages can be complicated, it’s stressful for managers because features take longer to complete, and it’s stressful for users (and QA for that matter) because issues will arise which are hard to reproduce and complicated to explain.

In the midst of all the work of migration, the rest of the company is still working: the security team is announcing bounties on our site which means we need to be vigilant about fixing issues, project management continues to come up with features to be added, the site perseveres in its never-ending quest for a new look and feel, and Firefox 4 is using AMO like never before meaning approaching 10,000 hits per second is a regular day. All of that is specific to the add-ons site, but consider your own company if you’re thinking of going down the same road – what is coming up for your site that will throw a wrench in the works?

The meat and potatoes of it really comes down to: Given the hindsight of today, would the migration be a good idea? There isn’t a right answer for every site, but for AMO we did the right thing[1]. As of today the majority of pages that matter are on Python – there are some admin tools, and some cron jobs, and the occasional semi-obsolete public page that is on PHP, but for the most part, we’re looking really good (less hand waving, more real data). My new (overly optimistic?) plan is to have PHP off by the end of this year. We’ll see.

To give you an idea of man-hours, we’ve had anywhere from 3 to 6 superhero developers working on the site over the past 15 months, and it’s looking like the whole thing will take around 24 months. That’s a big chunk of time for a site that needs to grow and evolve as quickly as popular sites do these days.

So, overall, I think the lesson is: any reasonably sized site is going to have rabbit holes in it. At first glance AMO might look like it’s got a dozen “main” pages, with a couple dozen more supporting pages (and throw in a few more for the admin CRUD). Have a look at that spreadsheet I linked above and you’ll see that’s not even remotely the case. The spreadsheet even ignores sub-pages in a few places and doesn’t include any new features added in the past year. If you’re considering a migration, think it through well. Make a spreadsheet of every URL, identify the complicated areas, and make sure everyone is clear on the timeline and what it means for new features. People will absolutely try to scope creep your migration – make it clear if a section of the site is migrating as-is or can be migrated and redesigned at the same time. Redesigns add complexity for the developers but can earn you some good will with the users and managers and if you’re in this boat you can use all the good will you can get.

May you have the best of luck with your decisions.

[1] I’ll write another post about pros/cons of the actual frameworks and platforms. Let’s just assume we’re happy with the technical side of the switch for now.

I stayed up late a few nights ago and wrote a script to raise an alert when something has changed. On its first run the script will recursively walk a directory tree hashing each file and storing the hashes in the directory (in an md5sum compatible formatted file). On subsequent runs it will begin tracking new files automatically but it will also print messages for missing and changed files. By saving the checksums in each directory it becomes portable – you can copy a directory somewhere else and still be able to verify nothing changed (a quick md5sum -c checksums.txt will let you know).

By default the script only prints messages when it sees something fishy so it’s perfect to drop into cron and it uses exit statuses so it’ll work for nagios too. I’ve been running it for a few months and have found a couple files that have changed – nothing critical yet but it’s nice to know it’s there.

Our main issue was hitting a memory limit or the max execution time. We hit the limits often for a variety of reasons, some legitimate bugs, and some because we tried to hack around things to make the tests run. If we change the limits we affect the tests because they are running within the same environment. There wasn’t really a concept of fixtures then, although it looks like CakePHP has stepped up there. The simple test web runner was hard to use and the mock objects were sometimes a little too mocked and missing some attributes.

All in all it was a heroic effort to get that many tests, but we didn’t maintain it because they were so slow to write and difficult to run. Testing can be a pain to write, sure, but it shouldn’t be a burden like that. Enter Django’s testing suite (built on top of Python’s unittest). It has most of our complaints handled out of the box. It’s very well documented, considers a lot of aspects of testing, supports fixtures, a built-in client, etc. It’s a well thought out framework to build tests on.

We’re being more vigilant about requiring tests this time around, but they also aren’t as frustrating to write. When you write them they actually work and they stay working. Most of what you want is built in already. For example, I wrote the password reset form we needed on AMO in Django. With CakePHP and SimpleTest I’d have no idea how to test that the email was actually working. It’s apparently possible with a SimpleTest add-on and enough code that I have to scroll in my browser. With Django’s test suite the actual code was 5 lines, 3 of which were assertions:

    def test_request_success(self):
        self.client.post('/en-US/firefox/users/pwreset',
                        {'email': self.user.email})

        eq_(len(mail.outbox), 1)
        assert mail.outbox[0].subject.find('Password reset') == 0
        assert mail.outbox[0].body.find('pwreset/%s' % self.uidb36) > 0

With the power of the new test suite we’re once again writing and maintaining our unit tests – currently at around 390 tests and increasing steadily. Plenty of people have written about why unit tests are important so I won’t belabor the point, but I will mention that it’s a great feeling to be able to commit something and be confident it hasn’t affected other parts of the site. It’s almost as good of a feeling when you write your code and a completely different test fails pointing out a case that you didn’t even consider but one that would soak up developer time trying to debug down the road.

Building on a foundation that takes testing seriously is great.

We hit some limitations with the NetScaler that we weren’t happy with. Cost aside, it ignored some pretty standard stuff like the HTTP Vary Header. After working around that for years we switched to the horizontally scalable Zeus Traffic Manager (at that time, referred to as ZXTM). We’ve been pleased with our choice and six months ago I wrote a similar PHP library that allows you to connect to Zeus’s API. Time and priorities being what they are, we never implemented it in production.

Finally, the real point to this post, last night I wrote a python library that will expire content from Zeus. We’ll roll this into our migration and waiting on content to expire from Zeus should be a thing of the past.

As always, if you can use the libraries, feel free. They all have READMEs with examples.

First out of the chute was the .po files. It turns out the actual formatting is different between the two languages. PHP uses %1$s for its substitutions, but python uses either named variables like (num)s or integers like {0}. For the record, they both support %s when you don’t need to order the substitutions.
PHP example:
I have %2$s apples and %1$s oranges
Python example:
I have {1} apples and {0} oranges

Since I’ve worked with the Translate Toolkit before, I decided to write a script to convert between the two formats. If you find yourself in the same unfortunate boat as me, behold
phppo2pypo and pypo2phppo to convert between the two types.

Crisis averted, right? Oh, that’s just scratching the surface. Remember how happy I was that PHP finally started supporting msgctxt? Well, Python has had a patch for it since 2008 but no one has bothered to land it. I wrote a new ugettext() and ungettext() that recognizes context in the .po files. To use simply do: from l10n import ugettext as _ at the top of your file.

Along with adding msgctxt support, those two functions also collapse consecutive white space. We’re using Jinja2 with Babel and the i18n extension as our template engine. Jinja2 has a concept of stripping white space from the beginning or end of a string but does nothing about the middle. A paragraph of text in a Jinja2 template would look like:

{% trans -%}Mozilla is providing links to these applications
as a courtesy, and makes no representations regarding the
applications or any information related thereto. Any questions,
complaints or claims regarding the applications must be
directed to the appropriate software vendor.
{%- endtrans %}


That’s a decent looking template, right? Yeah, well, when Babel extracts that, it includes all the line breaks too, giving you something like this. The localizers would revolt if I sent them that, so I added in auto white-space collapsing. Getting Babel to use the new functions means a new extraction script.

At this point, we’re extracting strings from our new code and we can convert between Python and PHP files. All we need now is a Frankenstein mix of xgettext functions to act as glue. Meet the amalgamate script that uses the pypo2php scripts, concatenates the .pot files, and merge updates each locales .po file. After that it’s quick tweaks to the build scripts to create z-messages.po files and we’re done.

So, all that said, the new process for L10n, while we’re in this transitional phase, is:

1. From the PHP code, run locale/extract-po-remora.sh. That pulls everything from all the PHP files, creates locale/r-keys.pot, updates the messages.po file for each locale, and compiles them. Life used to be so simple.
2. From the python code, make sure you’re up to date, then run ./manage.py extract. That will pull everything from the python code and templates and create locale/z-keys.pot.
3. Run ./manage.py amalgamate. That will merge the z-keys.pot into the PHP messages.po files.
4. Localizers can make their changes as usual, and commit back to messages.po.
5. From PHP, locale/copy-to-zamboni.py locale will create z-messages.po files in the Python format. We could skip right to .mo files, but in case something goes wrong I want to see the .po files.
6. Then, like today, locale/compile-mo.sh locale will compile all the .po files.

After all those steps are done, we’ve got duplicate .mo files, aside from formatting, and each application can look at its own .mo to get the strings it needs. All this code is just a big band-aid and there are plenty of things that are more fun than juggling L10n between two applications across two RCSs. But we knew what we were getting in to. I’ll post something more positive later to help justify it.

Migrating from CakePHP to Django

This is a big undertaking and we’ve been discussing it for quite a while. We’re currently the highest trafficked site on the internet using CakePHP and along with that we’ve run into a lot of frustrating issues. CakePHP has serviced AMO well for several years, so it’s not my intention to bad mouth it here, but I do want to give a fair summary of why we’re moving on. Please also note that AMO is still running on CakePHP 1.1 which is, I think, a year out of date? Three substantial issues:

• Useful Database Abstraction Layer: CakePHP has a concept of database abstraction, but we didn’t find it powerful enough. When it did work it would return enormous nested arrays of data causing massive CPU and memory usage (out of memory errors plague us on AMO). When it didn’t work, we’d end up doing queries directly which kind of defeats the purpose. We couldn’t use prepared statements so we’d have to escape variables ourselves. There was no effective caching built-in and since we just had huge arrays as a response there was no effective way to invalidate the cache we were using (see: Caching is easy; Expiration is hard). The DB layer should return objects that are easy to cache and easy to invalidate. The built-in Django database classes (combined with memcache) should work fine for us here.
• Effective unit tests: I’ve beat the drum about our unit tests before but the simple matter is that it’s really difficult to do them right with the tools we are using. Our test data is already very limited, but if we try to run all our tests right now they’ll run out of memory (and take forever). The CakePHP method of mocking controllers and models was inadequate for what we needed and difficult to deal with. We want our unit tests to run quickly, from the command line, and be independent from each other so there aren’t intermittent problems to waste our time with. We’ll be using Django’s built-in testing framework.
• Better debugging: Debugging in CakePHP amounts to defining a DEBUG level and seeing what is printed on the screen (usually the giant arrays). We supplemented this with Xdebug where we needed it, but that’s still not enough. A framework should have excellent logging and on-the-fly debugging that displays a full traceback (often something will fail deep within CakePHP and we’ll get the file/line where PHP gave up, but not the line in our code that started the problem), the values of variables, the page headers, server settings, SQL that was run, what views and elements are in use, etc. We’re planning on using a combination of pdb, IPython, and the django-debug-toolbar to make all of this easily accessible while developing.

Those are the major issues we’re having right now, but if you want to dig into the comparison some more check out our discussion wiki pages, but realize the majority of discussion happened in person.

Moving away from SVN

We moved AMO into SVN in 2006 and it’s treated us relatively well. Somewhere along the line, we decided to tag our production versions at a revision of trunk instead of keeping a separate tag and merging changes into it. It’s worked for us but it’s a hard cutoff on code changes, which means that while we’re in a code freeze no one can check anything in to trunk. As we begin to branch for larger projects this will become more of a hassle, so I’m planning on going back to a system where a production tag is created and changes are merged into it as they are ready to go live.

Most of the development team has been using git-svn for several months and, aside from the commands being far more verbose, we haven’t had many complaints. We’ve discovered Git is a much more powerful development tool and we expect to use it directly starting some time next year. As of now, we expect to maintain the /locales/ directory in SVN so this change doesn’t affect localizers but we’ll keep people notified if there are any changes to that process.

Continuous Integration

I mentioned excellent testing being one of the reasons we’re moving to Django. Along with that testing is the opportunity for continuous integration. We plan on using Hudson as the framework for our continuous integration. With excellent test coverage and quick feedback from Hudson this should drastically lower our regressions and boost our confidence when we deploy. Speaking of which…

Faster Deployment

For most of 2009 we’ve pushed on 3 week cycles. 2 weeks of development, 1 week of QA and L10n. Delays and regressions being what they are, I think we averaged a little better than a push a month. This is a fairly rapid cycle for a lot of development shops, but I feel like it’s holding us back. We’ve heard a lot of success stories about shorter cycles and I’d like to aim for deployment (optionally, of course) of a few times per week. By shortening the development cycle we reduce the stress of:

• the developers: Everyone likes to see what they’ve done go out quicker and it means less conflicts with others when the patches are smaller.
• the QA team: Right now we dump 2 weeks of work on them and say we need it done right away. With smaller cycles they can verify small changes as they go and not be overwhelmed.
• the infrastructure team: Smaller changes means less to go wrong and with a continuous integration server and some automation they can have minimal involvement with the whole process.
• the localizers: Every time we release we dump a bunch of changes on these fantastic people and tell them we need them back in a week. Most of the time they plow forward and get them done on time. If they don’t though, they are stuck with waiting for the next 3 week cycle. If we push often, it’s not a big deal.
• the product managers: These guys come up with crazy ideas for us to implement and then they stare at graphs and numbers to see if it worked. With shorter cycles they can get faster feedback about what works and what doesn’t.
• the users: Faster release cycles means bugs that are fixed in the repository are fixed on the live site sooner. ’nuff said.

Process Data Offline

Much of AMO relies on cron jobs to get things done. All the statistics, add-on download numbers, how popular an add-on is, all the star rating calculations, any cleanup or maintenance tasks – these are all run via cron and they are so intensive that the database has trouble keeping up. We’re planning on utilizing Gearman to farm all this work out to other machines in incremental pieces instead of single huge queries. Any heavy calculating that can be done offline will be moved to these external processors which should help improve the speed of the site and make all our statistics more reliable (as currently the cron jobs have a tendency to fail before they are complete).

Improve the Documentation

Documentation is a noble goal of many developers but it rarely gets enough attention. We evaluated our current documentation and found it is woefully out of date. By being on a wiki that is rarely used it doesn’t get updated except when someone tries to use it and sees it’s not right. We’re hoping to change that by moving the developer documentation into the code repository itself. We’ll be able to integrate with generated API docs, style the docs however we want, and check in changes right along with our code patches. When someone checks out a copy of AMO, they’ll get all the documentation right along with it. We’ll use Sphinx to build the docs.

The outline above details several large, high-level changes but there are a lot of other plans for smaller improvements as well. This post got a lot longer than I was expecting, but I’m really excited about the direction AMO is headed for 2010. As these changes are implemented the site will become more responsive and reliable, and we’ll be able to adapt to the needs of Mozilla’s users even faster. As always, feedback and discussion are welcome and stay tuned for further back end improvements.

I can look at them any time, and there are a few on flickr that other people can look at, but what about people that aren’t tech savvy or are really busy and get caught up in the daily grind?

I was thinking, the answer can be a really simple script running from cron, say, weekly. It picks a random photo from a directory and emails it to a group of people. That’s it. The idea is:

• it’s low tech compared to RSS feeds and social networking sites. This “just works” with the tools people (potentially, low-tech people) are already used to using.
• in a similar vein, commenting and discussion are built in if you feel like it.
• it’s focused on the people on the CC list. Sending out an old photo that is relevant just to those people has a lot more effect than one scrolling by on flickr. It’s got a personal touch.
• it’s automatic. You wake up Monday morning, drag yourself to work, and there is a photo from 15 years ago in your inbox and you can laugh about how bad your hair was. Awesome.

So, I thought I would try it and cooked up audreytoo. Basically, you seed a directory with copies of the pictures you want to send out, add the script to a cron job, and it does it’s thing. There are a couple other features in the script that you could look at if you want to get fancier.

I realize there is some irony in using an automated script to say “I’m thinking of you” but as long as I’m on the CC list it’s still true. Anyway, I’m sharing the code in case anyone else can find value in it.

One evening I decided I wanted to try making an IRC bot (because you know we need more of those!). I’d only worked with Python briefly before, but armed with the confidence only a language that you don’t know the shortcomings of can bring, I started writing code. After less than an hour and about 85 well-spaced lines of code later, Aaplsauce was born. All it does is sit idle in a channel and watch for someone to say something about AAPL. After someone mentions the magic phrase the bot looks up the price and prints it in the channel. How convenient!

So, nearly worthless? Absolutely. But the code is short and easy to write and python made that possible. Thx Python.

(yeah, if you read the code there is one other command the bot understands and, no, there’s no auth on it. Don’t make me do it! )