Please refer to the documents below.
J-GATE3.0 Connectivity Manual [Commonalities part]: "3.6 About Disaster Recovery"
J-GATE3.0 ITCH Connectivity Manual: "5.1 During Disaster Recovery"
Also, since OUCH NG is not provided at the secondary site, OUCH users must prepare measures to continue business through OMnet API in case of a switch over to the secondary site.