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This page defines the terms and requirements for FOLIO back-end modules related to the high availability.
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- Stateless - In the scope of the FOLIO back-end modules it means that neither session information nor business flow-related data is retained in the memory or local file system or other persistence mechanism managed by a particular module instance. Relevant data is sent to the module by the client in such a way that every HTTP request can be understood and handled in isolation without context information from previous or simultaneous requests. There is nothing that leads to the dependence of one HTTP request on another except the content of the database or another shared persistent storage available to all instances of the module. This does not apply to any sort of soft data (caches) that can be easily read from the persistent storage.
- Horizontal scaling means that adding more instances of a particular module to (or removing redundant instances from) the deployed FOLIO platform does not affect, break, or disrupt existing business flows or user sessions in any way.
- High availability (HA) is refers to the ability of a system to operate continuously without failure for a designated period of time. HA works to ensure a system meets reliably, without unplanned interruption, at an agreed-upon operational performance level . For the FOLIO platform, the HA in a particular environment can be achieved using horizontal scaling for back-end modulesof service. This is a characteristic of how a system is deployed and operated. To allow for HA deployment, Folio incorporates design elements that allow hosting operations to use horizontal scaling, redundancy, and automated failovers.
Requirements for the FOLIO back-end modules
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