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7. Reliability > Dependencies

Dependencies

Every failure has its origin in a dependency. To minimize failures, minimize dependencies.

On the other hand, there is often a good economic reason for a dependency. For example, a program that uses shared libraries is dependent on those libraries; it will not run without them. A change to the system libraries, or to the path used to look for them (LD_LIBRARY_PATH), may break the program. But in return for this dependency, you get an executable that is smaller. The alternative is to use a statically linked program, which is larger because it includes the libraries, but cannot be broken by a change in the system libraries or the library path.

Another good example is how many applications you should run per box. If you run dozens of applications on one machine, each can affect the other. Worse, it is not easy to figure out which one is misbehaving at any point. If you run each application on its own box, they cannot affect each other directly and you can instantly tell which one is misbehaving, but it’s much more expensive to have that extra hardware. Computer room floor space can cost more than the computers that sit on it, so having more physical machines is expensive for both reasons.


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