Question about Redundancy with New Hardware IO Servers

Hi Alan,

What you want to do is called "Online upgrade" and Citect/Plant SCADA supports that. However, you need to do it a specific order which is primary first. Redundancy will be preserved and communication will work regardless of hardware.

Link to 2018 online upgrade help:

Online Upgrade | Upgrading (aveva.com) (gcsresource.aveva.com/.../Online_Upgrade.htm)

Thanks Bradley

Alan 

The pair of I/O servers on new and old hardware will not achieve the I/O redundancy if the project network addresses are configured with IP addresses 10.15.34.71-72 for the old I/O server pair while the new OS machines use 10.15.34.73-74. It is because clients won't know the IPs of new servers.

To achieve the I/O redundancy for this online upgrade scenario (hardware upgrade), you should assign the same IPs to the new machines and connect them one by one to LAN once the project is ready for deployment. The old one needs to shutdown before its replacement joins the network.

Hope this would help.

Many Thanks Jacky

Configuring the project with host names instead of IP addresses could remedy this. You will need a DNS server though.

appreciate the reply Patrick.

i was wondering what the clients looked at server name or IP address?

If I'm not mistaken, clients will try to connect to a server by looking up the Address field from the Network Addresses configuration. In your screenshot these are IP addresses.

In my projects I use computer host names if possible. Clients will then use standard lookup mechanisms like DNS, or hosts files to resolve the IP addresses.

In your case you need to change this in your old and new projects on all machines involved.

Patrick is right. Clients will use DNSQuery(hostname) to retrieve the server IPs and then make connections to servers. If an IP instead of Hostname is passed, the IP is directly returned. Using hostnames in Network Addresses have many advantages.

• Static IPs are no longer required
• Simplify the configuration for redundant networks
• Achieve I/O redundancy for Connectivity Server (available from 2020R2 or 8.30 release)
• Easy to replace damaged hardware.

The above screenshot indicates that the project is configured with IPs not hostnames. However, I recommend that you should keep using IPs in Citect SCADA 2018 to avoid some implication in alarm redundancy with hostnames that was reported by some customers. Using hostnames had been enhanced in Citect SCADA 2018R2 because of the encryption in communication that requires hostnames for certificate binding. Updating your project with hostnames in the next software upgrade would be a better option, I think.