SQL Server from container - Before jumping into the bandwagon

It is easy to get started on development and simple testing using SQL containers. It was discussed in the previous post. But before putting into production and start developing real applications we had to make sure the below things at least.

SQL Server running inside Linux container doesn't mean its free

People from the Linux world or in general people tend to think that everything in Linux is free. But that is not true in the case of SQL Server similar to other enterprise software running in Linux. In order to use the SQL Server container in production, we need a valid license even in the Linux containers.

Configuring and operating

Running and operating containers is an added skill to the operation teams. We need to make sure our client or in-house operational teams are capable of doing it.

Feature parity

There are many factors influencing feature differences. Microsoft always says its the same codebase but features don't reflect that. Let's see the factors that decide features

• Versions - Obviously there will be differences between SQL 2016, SQL 2017, and SQL 2019 features. The codebase is never the same though the latest may be built on top of the previous.
• Editions - First level feature difference inside the same version is based on the edition. This is regardless of wherever we run the SQL instance. This makes sense as we need to give more money to unlock features. This is there from the early days of SQL Server.
• Running platform - There are feature differences based on where the SQL instances run such as standalone inside Windows OS, Azure, and Linux containers.
• Azure PaaS platform - Inside Azure, there are Azure SQL and Azure SQL managed Instance models. They have many feature differences.

The containerized SQL server is more like the Azure SQL than compared with desktop SQL installation. Features such as FileStream, CLR support are not available in SQL container. The full list of features that are not supported in the SQL container can be found here.

Production readiness

As per Microsoft, SQL Server on Windows Container is not production-ready. But SQL Linux containers are production-ready. They have documentation on High availability when running SQL Linux containers and how to orchestrate using Kubernetes.  But not sure currently companies are investing to just move their SQL workload to a containerized production environment. 

Everyone agrees to start using it for development and testing. Eventually, when more workloads start using the SQL Server Big Data Cluster features, production will also start using SQL Server in containers. There are also documentation says SQL container as is don't support clustering hence the DR can be done only by log shipping. The Kubernetes based HA for SQL containers may not be instantaneous for an RDBMS database like Always On Availability Groups or FCI. It may take some time to detect the failure and start the next container instance.

As of now, my takeaway is not to use SQL containers for critical production workloads.