Overview
The Survey Solutions supports horizontal scaling and may be deployed as a web-farm for servicing a large number of client connections.
This is especially important for operations like population censuses and large national surveys.
A web-farm installation is implemented on multiple systems (called nodes) working in concert to service the received requests. Increasing the number of nodes in the farm allows to improve the overall performance: the responsiveness of the system and number of users working simultaneously.
The number of nodes in the farm may be dynamically changed (new nodes introduced or existing nodes shut down) without the interruption of work of the other nodes.
The overall performance of the web-farm is determined by the performance of individual nodes (higher processing power, memory, and drive speed will positively affect the overall performance).
The exact moment when a web-farm must be introduced depends on multiple factors, including the desired responsiveness, number of simultaneous users, performance of the nodes, size and complexity of the questionnaire.
Even a very powerful web-farm may still be limited by the bandwidth of the internet connection, which must be taken into account when the Survey Solutions deployment is being planned.
Deployment scheme
For Web Farm mode Survey Solutions Headquarters should run behing load balancer or reverse proxy with load balancing capabilities. Load Balancer should support Web Sockets and sticky sessions. Modern reverse proxy servers are already support this.
Survey Solutions require that both WebSockets and StickySessions are enabled for all survey modes.
Survey Solutions Configuration
For Survey Solutions Headquarters configuration following settings should be enabled for ALL instances of HQ in [Scheduler] settings
[Scheduler]
InstanceId=AUTO
IsClustered=true
IIS
It’s possible to run IIS in Web Farm mode - https://docs.microsoft.com/en-us/iis/web-hosting/scenario-build-a-web-farm-with-iis-servers/configure-a-web-farm-with-iis-servers