Increasing the availability of a service through Hot Passive Replication

Abstract: This bachelor thesis examines how redundancy is used to tolerate a process crash fault on a server in a system developed for emergency situations. The goal is to increase the availability of the service the system delivers. The redundant solution uses hot passive replication with one primary replica manager and one backup replica manager. With this approach, code for updating the backup, code for establishing a new primary and code to implement fault detection to detect a process crash has been written. After implementing the redundancy, the redundant solution has been evaluated. The first part of the evaluation showed that the redundant solution can deliver a service in case of a process crash on the primary replica manager. The second part of the evaluation showed that the average response time for an upload request and a download request had increased by 31\% compared to the non-redundant solution. The standard deviation was calculated for the response times and it showed that the response time of an upload request could be higher compared to the average response time. This large deviation has been investigated and the conclusion was that the database insertion was the reason.