Budapesti Műszaki és Gazdaságtudományi Egyetem Méréstechnika és Információs Rendszerek Tanszék Hibatűrő rendszerek tervezési mintái Segédfóliák az Autonóm és hibatűrő inf. rsz. tárgyhoz Kocsis Imre

Ismétlés: singleton

Ismétlés: Facade

Ismétlés: Observer

Architekturális mintanyelv

Units of Mitigation  How can you keep the whole system from being unavailable when an error occurs?  „Design the system into parts that will contain both any errors and the error recovery. Choose the divisions that make sense for your system. Design the rest of the system around these parts that represent the basic units of error mitigation.”

Correcting Audits  Faulty data causes errors.  „Detect and correct data errors as soon as possible. Check related data for errors, correct and record the occurence of the error.”

Redundancy  How can we reduce the amount of time between error detection and the resumption of normal operation after error recovery?  „Provide redundant capabilities that support quick activation to enable error processing to continue in parallel with normal execution.”

Minimize Human Intervention  How can we prevent people from doing the wrong things and causing errors?  „Design the system in a way that it is able to process and resolve errors automatically, before they become failures. This speeds error recovery and reduces the risk of procedural errors.”

Maximize Human Participation  Should the system ignore people totally? That will reduce procedural errors.  „Know the user and their availability. Design the system to enable knowledgeable operating personnel to participate. […] Provide appropriate Maintenance Interfaces and Fault Observer capabilities […]”

Maintenance Interface  Should maintenance and application requests be intermingled on the application input and output channels?  „Provide a separate interface to the system for the (almost) exclusive use of maintenance interactions.”

Someone in Charge  Anything can go wrong, even during error processing. When this happens the system might stop doing the error processing in addition to not doing the normal processing.  „All fault tolerance related activities have some component of the system that is clearly in charge and has the ability to determine correct completion and the responsibility to take action if it does not complete correctly.”

Escalation  What does the system do when its attempt to process an error in a component is not acheiving the correct effect?  „When recovery or mitigation is failing, escalate the action to the next more drastic action.”

Detektálási minták

Fault Correlation  What fault is activating?  „Look at the unique signature of the error to sort it into the fault category for which error processing steps are known.”

Error Containment Barrier  What is the first thing that the system must do when it detects an error?  „Isolate the error to a unit of mitigation. Stop the error flow with a barrier, quarantine and initiate either error recovery or error mitigation.”

System Monitor  How does one part of a system keep track that another part is alive and functioning?  „Create a Monitor to study system behavior, or the behavior of specific parts of the system to make sure that they continue operating correctly. When the watched components stop, the monitor should report the occurence to the Fault Observer and initiate corrective actions.”

Detektálási minták

Existing Metrics  How to measure the severity of an overload without contributing to the overload?  „Use pre-existing indicators already tied to the resource as an indicator of the system’s overload condition.”  Megjegyzés: nem csak a teljesítményre igaz!

Detektálási minták

Routine Maintenance  How can we keep preventable errors from occuring?  „Perform routine, preventive maintenance on the system.”

Detektálási minták

Routine Exercises  How do you know that Redundant elements that will be called into service by a Failover in case of an error or failure will actually work?  „Routinely exercise, or execute the system components that will be required in an error situation. This will identify latent faults.”

Detektálási minták

Helyreállítási minták

Quarantine  How can the system prevent errors from spreading?  „Establish a barrier around the element that prevents it from both contributing to the useful work and also prevents it from propagating its error into other parts of the system.”

Helyreállítási minták