Add section on configuring backups from replica node (#58696)

Co-authored-by: Sam Browning <[email protected]>

Author: khanhgee

content/admin/backing-up-and-restoring-your-instance/backup-service-for-github-enterprise-server/configuring-the-backup-service.md

@@ -125,7 +125,7 @@ If you're migrating from {% data variables.product.prodname_enterprise_backup_ut
 
    Use the `--dry-run` flag to preview changes without applying them.
 
-### Scheduling automated backups
+#### Scheduling automated backups
 
 Once the service is configured, you can define a backup schedule.
 
@@ -134,3 +134,27 @@ Once the service is configured, you can define a backup schedule.
 1. Click **Save** to apply the changes.
 
 The first run will be a full backup. Future runs will be incremental. If a new backup attempt starts while a previous one is still running, it may be skipped or fail. In that case, adjust the schedule to avoid overlap.
+
+{% ifversion ghes > 3.19 %}
+
+### Configuring backups from a replica node
+
+For high availability, you can designate a replica node as your backup server. To minimize latency, {% data variables.product.github %} recommends picking a replica node in the same region or datacenter as your primary node.
+
+> [!IMPORTANT] 
+> Backups from cache replica nodes or active geo replica nodes are not supported.
+
+To configure your backup server, run the following commands, replacing `HOSTNAME` with the hostname of the node:
+
+```shell
+ghe-config cluster.HOSTNAME.backup-server true
+
+ghe-config-apply
+```
+
+You can now run `ghe-backup` directly on your replica node.
+
+> [!WARNING]
+> Due to the latency between primary and replica nodes, you may lose data when backing up from a replica node.
+
+{% endif %}