In systems design, a fail-fast system is one that immediately reports at its interface any condition that is likely to indicate a failure. Fail-fast systems are usually designed to stop normal operation rather than attempt to continue a possibly flawed process. Such designs often check the system's state at several points in an operation, so that any failures can be detected early. The responsibility of a fail-fast module is detecting errors, and then letting the next-highest level of the system handle them.

Hardware and software

Fail-fast systems or modules are desirable in several circumstances: Developers also refer to code as fail-fast if it tries to fail as soon as possible at a variable or object initialization. In object-oriented programming, a fail-fast-designed object initializes the internal state of the object in the constructor, launching an exception if something is wrong (rather than allowing non-initialized or partially initialized objects that will fail later due to a wrong "setter"). The object can then be made immutable if no more changes to the internal state are expected. In functions, fail-fast code will check input parameters in the precondition. In client-server architectures, fail-fast will check the client request just upon arrival, before processing or redirecting it to other internal components, returning an error if the request fails (incorrect parameters, ...). Fail-fast-designed code decreases the internal software entropy and reduces debugging effort.

Examples

Business

The term has been widely employed as a metaphor in business, dating back to at least 2001, meaning that businesses should undertake bold experiments to determine the long-term viability of a product or strategy, rather than proceeding cautiously and investing years in a doomed approach. It became adopted as a kind of "mantra" within startup culture, i.e. "Fail fast, fail often."