What Does "Fast" Mean?

Reuven Lerner — Mon, 21 Mar 2016 19:01:38 +0000

Good news! One of my clients is launching a new marketing campaign, which we expect will make the business even more successful than before.

Bad news! This means our Web application, which has existed for some time on a fairly simple infrastructure, and which has handled a steadily growing number of users, now (we hope) will need to deal with a massive spike in users.

The big question is this: can our servers handle the load we expect? Indeed, what load can we expect? And, what happens if we need to crank up even more capacity?

So in this article, I walk through some of the basic points having to do with Web scalability, describing a few of the key things to keep in mind. Next month, I'll take a deeper dive into these ideas and discuss some of the techniques you can use to improve the speed—or apparent speed—of your applications.

Background

Many of my clients are companies that need a Web application, but aren't familiar with the ways in which the Web works. A common question for them to ask me is "We have many thousands of users every month. Can the server handle that many people?" When I explain that users consume server resources only when they actively are making an HTTP request, their understanding begins to improve. A company with 10,000 visitors a month doesn't need to worry about 10,000 simultaneous visitors; they likely will have some periods of time with a few dozen and other periods of time with absolutely none. Thus, scaling up their infrastructure to handle 10,000 simultaneous users would be foolish.

At the same time, there are times—such as after launching an advertising campaign or being mentioned on a TV show—that you indeed will have a huge spike in traffic. Companies that advertise during the Super Bowl not only expect to get millions of viewers, they also expect to have many of those people visit their Web sites after (or during) watching the ads. This means normal assumptions for scaling no longer are applicable.

This is one of the reasons why Amazon's EC2 has become so popular. If you can treat a server as a commodity, paying for it by the hour and spinning servers up and down as necessary, you can solve this scaling problem. As traffic rises, you add more servers. As it falls, you remove them.

But of course, life is more complicated than that. First and foremost, every system has bottlenecks that can't just be wished away by auto-scaling. For example, if it turns out that your database can't handle a large load and you have only a single database server, auto-scaling your Web servers may exacerbate the problem, rather than solve it.

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Scalability

What Does "Fast" Mean?

Background