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host an emulated virtual drive on App Engine, but these are not part of the product
offering at this time.
Running all these services on behalf of your application isn't something App
Engine handles without restrictions. Your application gets a daily limit on each type
of request, and each request is recorded and then subtracted from your daily
allotment. Let's take a deeper look at these quotas.
Being a Good Neighbor With Quotas
As we mentioned in Chapter 1, App Engine is a multitenant platform. This is far
different from hosting your application on a dedicated server or in your own data
center. The fundamental difference is that you're not alone! Thousands of other
developers are using the same network, hardware, and computing power that Google
is offering for use with your applications. At first glance, this might create concern
about scalability. Keep in mind that Google is the third largest e-mail provider on the
planet and your free App Engine account can scale to five million hits per day. Plus, if
you need more than that, you can always pay for more resources.
What if you shared a water source with your next-door neighbor? You wake up on
Monday to get ready for work, turn on the shower, and nothing happens. You take a
look out the window and notice that your neighbor left the hose on all night after
washing his car that afternoon. This shared environment with no restrictions or quotas
can be risky. How do you know if you're using too much or if you're neighbor is taking
more than his allotment? To protect users from this similar situation with respect to
computing power, multitenant platforms use application quotas or governor limits to
enforce application restrictions on users. For example, you can have a maximum of
7,400 secure incoming requests per minute on a free App Engine application. With
billing enabled (more on that later in this chapter) you can have 30,000 secure
incoming requests per minute. The point is, there's a limit on what you can use. This
protects other users on the same platform from being affected by applications that
have significantly more traffic and resource needs. (This is known as “the slashdot
effect.” See .)
Note If you need more resources than the billing-enabled quotas allow you can request an increase by visiting .
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