The story of hgstats

17 Aug 2014

tl;dr: I built a thing to see public graphs of hg.mozilla.org called hgstats.

Lately, we’ve had problems with Mercurial at Mozilla. The Developer Services Team added a bunch of instrumentation to the hg webheads to help us track what is going wrong and when, to give us somewhat an early indicator of when things get shot to hell. All of these are on the Mozilla Graphite instance which are behind employee-only LDAP. However, an interesting quirk is that the image rendering is actually available without authentication. As a community Sheriff, I’ve been keeping close watch on hg throughout my shift with images that releng folks or hwine gave me. This gave an indicator of when to close trees so that we don’t end up having everything turn red. On Thursday evening, I was watching the conversation in #vcs on irc.mozilla.org, when bkero mentioned he’d made a dashboard in graphite. It suddenly dawned on me that I could just embed those images onto a page and quickly have a public dashboard!

Armed with a bunch of images from Ben, I created a github pages repo with a lovely theme that’s available by default. I embedded the images onto a static HTML page and suddenly, we had a minimal dashboard. It wouldn’t auto-refresh or let you alter the duration of the graph, but hey, now we had one place for things! This first step took about 15 minutes.

There were two features I had in my mind as must-haves: a) the page must let me change the hours of the graphs (i.e. last 2 hours, last 4 hours, last 8 hours, etc), and b) it should auto-refresh. I’ve looked at backbone several times in the past and I figured this was a good time as any to get cracking on building a backbone.js app.

I started slowly, the first step was, get everything I have right now, rendered with backbone. I spent a lot of frustrating hours trying to get it to work, but couldn’t because of silly mistakes. I haven’t been coding in JS much and it shows :) I think I stayed up until 2 am trying to diagnose it, but I couldn’t. When I woke up in the morning, I spotted the trouble immediately and it was a tiny typo. Instead of <%=, I typed <%$. After that first step, I got the router bit working and I had an app that could dynamically change the range of hours in the graph! I’d met my first goal!

I talked to mdoglio who took a quick look at the code and thought models might be a good idea if I’m dealing with data. I refactored the code again to use models, which cleaned it up quite well! Overnight, I had a pull request from hwine to add another graph as well, which I also made more dynamic.

The hardest bit was getting auto-refresh working. I couldn’t figure out an easy way to solve the problem. Eventually, I ended up with setTimer, but the full credit for the right incandation goes to bwinton.

High Five!

Working with backbone has been great, but I wish the documentation did more than just tell me what each function did. Python’s documentation often gives you more than function’s description, it tells you how you would use it practically. Of course, there quite a few resources that already fill this gap. I found backbonetutorials.com pretty useful. I got most of the basic idea of backbone from the site.

I also submitted it to Webdev Beer and Tell (my first submission!). Mike kindly presented it for me (no, he’s not the real nigelb!) and you can watch the video on Air Mozilla if you have some free time :) I would totally recommend watching the whole video, but if you don’t have a lot of time, skip to 6:37.

This is the first time I’ve built a single-page app, so I’d love feedback (extra points if you can do a code review). The code is on GitHub.

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