How to fix Error 7877 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 7877 – Backup on Secondary Replica Not Supported in Contained Availability Group

Why This Error Happens

This error occurs because the client connection string is routing the backup operation to a secondary replica without properly specifying the contained availability group name in the connection context, causing SQL Server to reject the request since it cannot resolve the correct read-only routing or backup preference. It commonly happens when applications or backup tools use a direct server name or listener that does not explicitly reference the contained AG’s name property, which is required in SQL Server 2025’s contained availability group architecture. Additionally, a stale or cached connection to the instance may retain outdated metadata about the AG topology, preventing the backup preference settings from being honored correctly.

Step-by-Step Resolution Guide

Step 1: Verify the Backup Preference Settings on the Availability Group

  • Open SQL Server Management Studio (SSMS) and connect to the primary replica.
  • Run the following query to check current backup preferences:
  SELECT ag.name, ag.automated_backup_preference_desc 
  FROM sys.availability_groups ag;
  • Confirm whether the preference is set to “Secondary only,” “Prefer Secondary,” “Primary,” or “Any,” and ensure this aligns with your intended backup strategy.

Step 2: Update the Connection String to Reference the Contained AG Name

  • Ensure your backup script or third-party backup tool explicitly uses the contained availability group’s listener name or AG name, not just the instance name.
  • Example connection string correction:
  Server=AGListenerName;Database=ContainedAGName;Integrated Security=True;
  • If using PowerShell or sqlcmd, confirm the -S parameter points to the listener, not a standalone node name.

Step 3: Reconnect to the SQL Instance and Clear Cached Sessions

  • Fully disconnect all active sessions in SSMS or your backup application (close and reopen the tool rather than just refreshing).
  • On Windows Server 2025, restart the SQL Server service if the issue persists:
  Restart-Service -Name 'MSSQLSERVER' -Force
  • Re-establish the connection explicitly targeting the contained AG, then retry the backup job.

Step 4: Validate Contained AG Metadata Synchronization

  • Run DBCC CHECKDB and sys.dm_hadr_availability_group_states on the secondary replica to confirm synchronization health.
  • Check for replication latency or metadata mismatch errors in the SQL Server Error Log located at:
  C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG
  • If metadata is out of sync, failover to the primary temporarily and re-sync the secondary.

Alternative or Verification Steps

  • To verify the fix, manually initiate a BACKUP DATABASE command targeting the secondary replica with WITH COPY_ONLY and confirm it completes without throwing Error 7877.
  • If the issue persists, as a workaround, redirect backups temporarily to the primary replica by adjusting the AG’s automated_backup_preference to “Primary” until the contained AG connection metadata issue is fully resolved.