Managed Instance Gotchas – Error Conditions
I recently embarked on a project to migrate a highly transactional installation of SQL Server to Azure SQL Managed Instance (MI). As I delved into the migration process, I encountered several unexpected surprises that could have halted our progress if not addressed promptly. In this article, we'll explore the error conditions that may impede your MI migration, with the aim of helping you avoid or prepare for these challenges.
No Support for DNS Aliases
A crucial aspect to consider when planning your MI migration is the lack of support for DNS aliases. While using aliases might seem like an attractive solution to facilitate a smooth transition, it's essential to understand that Azure environment blocks these aliases, and using them would be fragile at best, and unsupported.
Coordinate Client Applications
A key consideration when migrating to MI is the importance of coordinating client applications. Ensure that your clients' systems migrate simultaneously with your server migration, as this will minimize disruptions to your users.
Zone Redundancy Issues
Zone redundancy is an attractive feature of MI, offering high-availability options by synchronizing servers between zones in Azure. However, we encountered significant problems with zone redundancy, including the discovery that our region did not offer this feature until the 4th quarter of this year.
Our experience highlights the importance of verifying the availability of desired features before planning your migration. Inadequate research led to unexpected delays and frustration. Ensure you thoroughly investigate the capabilities of your chosen region before proceeding with your migration.
PITR for SQL MI Backups and Restores
The traditional backup/restore process in MI environments is limited, and PITR (Point-in-Time Recovery) is the recommended method for backups and restores. While using a traditional, COPY_ONLY, backup method might seem like an easy solution, it's essential to understand that this approach is considered technical debt.
Fixing I/O Buffer-Related Issues
In our case, the issue with restore failures seemed to be I/O buffer-related. To resolve this problem, we employed specific options during the restore process. However, it's crucial to prioritize PITR for all MI processes, as it offers a more reliable and efficient solution.
SQL Agent Job Errors
SQAgent job errors were our final blocker for migration to SQL MI. These intermittent issues required investigation and changes to the servers, involving Microsoft support tickets. Thankfully, we were able to resolve these issues with the help of our Microsoft architect, but this experience highlights the importance of thoroughly testing jobs under load.
Thorough Testing and Planning
In conclusion, while migrating to SQL MI may seem like a straightforward process, there are several potential pitfalls that can hamper your migration. To increase your chances of success, it's essential to test thoroughly, engage with the technical team about hardware availability in your region, and be prepared to open tickets to resolve issues.
By understanding these error conditions and taking proactive steps to address them, you'll be better equipped to navigate the challenges associated with MI migration and ensure a smooth transition for your organization.