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On a high level the different scenarios for running Delft-FEWS in a highly available manner when the primary Azure region fails, from most high available to least available
Scenario | Description | Disaster recovery if primary regions fails | Manual interventions | Recover Time/Data Loss for Delft-FEWS components |
Dual MC in 2 Azure regions | 2 different databases in two regions, databases will be synchronized by Delft-FEWS. Use Geo redundant storage for file shares. | Automatically by Delft-FEWS. | Operator clients need to reconnect to secondary MC. This has been pre-configured. | No Recovery Time. (Hot Stand By) Data loss is minimal and can be restored by rerunning workflows. |
Single MC with Database in 2 Azure regions | Azure auto failover group Managed Instance Database with Azure Site Recovery for VMS. Use Geo redundant storage for file shares. | Use Azure Site Recovery to restore VMS in secondary region. Synchronized database will be made primary by Azure.
| Azure Site Recovery has to be enabled. | Recovery Time depends on the time it takes for Microsoft to enable ASR. Data loss is minimal and can be restored by rerunning workflows. |
Single MC with locally redundant Database | Single database with Delft-FEWS components | Database backups have to be restored to a new database in a secondary region. VM backups have to be restored to a secondary region | Database configurations on restored VMs have to be adjusted to new DB. Delft-FEWS configuration has to be adjusted to use new Database. | Recovery time is a few days. Data loss depends on the backup schedules. |
Disaster Recovery
This section will describe possible Disaster Recovery solutions for the different parts of a Virtual Machine based Azure system:
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