Lessons from live blogging with Azure (nothing bad happened)

posted by Jeff | Sunday, May 12, 2013, 1:57 PM | comments: 0

I wrote previously about how I built a "live blog" app in Azure, so we could use it for PointBuzz during last week's festivities at Cedar Point. Not surprisingly, it worked just fine. As I expected, the whole thing was kind of overkill. Sweet, over-provisioned overkill.

The traffic loads we encountered were not a big deal. At one point, we were close to 300 simultaneous connections. We didn't really need Azure to handle that, but the truth is that I wasn't entirely sure what to expect in terms of SignalR and its effect on the servers. What better reason to spin up virtual machines in Azure? I still think that's the biggest magic about cloud services, that you can turn on stuff just when you need it, and pay just for that. It sure beats having to buy or rent a rack of equipment.

The performance was stellar. Average CPU usage never went over 1.5%. I ran two instances of the MVC app as a Web role. I chose this over straight Web sites because of the distributed cache that comes free with it. Of course I didn't really need it, but why not? I didn't do any page rendering timing at the server, because grabbing a few objects out of the cache and making them into a simple page was probably stupid fast, but testing from the park's WiFi, the time from request to last byte (not counting images) was generally under 200 ms. The AJAX calls on scroll for more content were just slightly faster.

The CDN performance was similarly pretty solid. I did a few unscientific tests on that prior to our big day, comparing the latency of the CDN to direct calls to blob storage. Predictably, the first hit to the CDN was always slower as it grabbed the data from storgage, but after that, they were about the same. Again, this was not scientific, and I also can't control which point of presence I was hitting on the CDN. This was another feature I certainly didn't need, but figured I would try it since it was there.

We moved a total of 6 gigs of photos that day, which was a lot more than I expected. This isn't a big deal for a few days of activity, but if I were using this (or any of the cloud services) long-term, bandwidth costs would be a concern. They're still a lot higher than the "free" terabytes of transfer you typically get when you rent a box in some giant data center.

At the end of the day, the app proved two things. The first was that SignalR imposes very little overhead, even with hundreds of open connections. The service bus functionality, still in beta, works great, to shuttle messages between running instances of the app. The other thing that it proves is that I bet you could throw this simple thing up for a big live blog event like an Apple product announcement and it would work just fine. I need to find someone willing to take that chance now. :)

So what does all of this overkill cost?

166 compute hours (2 small instances): $13.28
6 gigs out of the CDN: $0.60
18,000 CDN transactions: $0 (it's a dime for a million)
11,000 service bus messages: $0 (it's a buck for a million)
1.2 gigs out from app: $0.10
200 MB storage: < $1
SQL database: < $5 for a month


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