I am new to VCS and am planning to use it for my COBOL based application. I want to have two servers in my prod environment Primary and Secondary. I want to support Automatic failover without disconnecting the users who access the COBOL application through putty. Could you please help me answer these questions:
(1) When I deploy code in Production, will I deploy only once on the virtual IP or I need to deploy on both Primary and Secondary separately?
(2) Once VCS is running and primary fails, will users get disconnected?
(3) Will the failover to the Secondary seemless or I still need to re-mount the storage, interfaces etc again on the secondary server?
(4) I dont want to use automatic script for failover as data which was in the buffer when server crashed is also critical. Hence if a DR type failover is required, I want to do it manually as I dont want to lose any data. Is it possible?
I don't have any feedback for COBOL in particular as I could not find any documentation anywhere in regards to how to cluster COBOL (using any cluster software). So, here is what I can tell you about clustering generic applications.
1) Deploy code in clusters: It is possible to deploy either on shared storage, or, locally. I prefer installing locally as it allows rolling upgrades for applications that support such. Typically:
2) What happens to users on node failure? This depends on your application. If there is middelware and a web front-end, then the user normally stays connected or only has to retry the transaction. If users are connected directly to the host, then they will be disconnected. They will have to reconnect. If configured properly, VCS moves the VIP/DNSname to the second host. Users/applications would reconnect as normal as the IP address is moved.
3) Storage: It is normal to configure VCS to manage everything needed to make an application run, including importing disks, mounting disks, updating NICs with the floating VIP, starting any processes. These confgiurations are detailed in the admin guide.
4) For local failover, most admins configure the failure between nodes as automatic, but this can be made maunal. For wide-area (DR) type failover, by default, the failover is not automatic and must be initialized by an operator. This prevents false positives situations such as loss of network/communications but the server is still running.
Regarding losing data when a hode fails:
Hope this helps.