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Complex network information systems are usually responsible for realizing client requests of business level services. Often these services are critical for the company and it is very important to ensure that appropriate reconfiguration will be applied in case of system malfunction. Due to the complexity of systems, huge amount of dependencies and impacting factors, the analytical approach may be too limiting to evaluate the reconfiguration policy. The paper presents a method of analyzing new applicable configurations of information systems based on simulation. As a result, the reachability graph of configurations is constructed. Each transition in the graph defines the most adequate reconfiguration (compliant with user criteria) in case of a system failure.

Software failures and human errors are the most common reasons of inoparability of computer systems. Computers are increasingly reliable, but the level of transcient faults, caused by errors hidden in the programs, remains the same. For this reason software is becoming the key factor in the synthesis of highly reliable systems. Software errors do not result from operation, they either exist from the start or are inserted when patching or upgrading it. Some errors result from incorrect human interaction or unexpected environmental changes. Assessment of software impact requires functional-reliability approach to reliability analysis: the software fault occurs when it causes incorrect operation and not when it is introduced to the system. It is proposed to use software reliability models in system analysis, to predict the intensity of software faults. The software recovery after a failure is realized by restarts of various extend (microrestarts, minirestarts and macrorestarts). The impact of software failures and restarts on system availability is assessed.

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