Azure Migrate is the name of an umbrella service for a collection of tools to aid in the assessment and migration of on-premises infrastructure, software, and data to the Azure cloud. In terms of infrastructure, you can assess physical and virtual servers by downloading an appliance in the form of a virtual machine image, either VMWare or Hyper-V, that will collect system and usage data about your on-premises environment. If, for whatever reason, spinning up a dedicated assessment VM isn't appropriate; there is a spreadsheet template you can download and fill in with server details and then upload to Azure Migrate. In either case, the assessment service will recommend virtual machines with vCPUs, memory, and disk characteristics that will best meet your needs. Along with the specifications, the assessment will display estimated costs for each virtual machine.

When it comes to assessing SQL Server databases for migration to Azure, there are currently two tools available within the portal. Microsoft Data Migration Assistant, DMA, is a free download to run on-premise, and UnifyCloud's CloudPilot is a third-party paid-for tool.

The Data Migration Assistant, as the name implies, also migrates SQL Server databases to Azure. Run the assistant on-premises to identify server instance and database compatibility issues with a target Azure SQL database type. While it is possible to assess AWS RDS for SQL Server as a source, the Data Migration Assistant doesn't support migrating it.

Data Migration Service is an online tool accessed through the Azure portal that will migrate SQL Server to Azure SQL databases of all types and non-SQL Server databases to their Azure counterparts.

Microsoft Data Experimentation Assistant is another downloadable tool that enables you to record an SQL Server workload as XEvents or a Trace and then replay the workload on a target server to assess how your workloads are likely to perform in the destination environment.

Of course, there is a lot of SQL code that resides outside of databases in application software. This is especially true with the rise in popularity of data access layers like Entity Framework that have encouraged embedding SQL scripts inside client applications instead of using stored procedures. Data Access Migration Toolkit is a Visual Studio Code extension that can analyze code for SQL statements producing a report outlining potential migration issues. Saving the report in JSON format enables you to upload it to the Data Migration Assistant incorporating the application layer into your database assessment. 

To close the loop, Azure Migrate includes tools and services to help with the data migration process. While, in theory, you could migrate a database server using the server migration functionality to a VM, it would be fraught and, in all practicality, not worth the effort or tears. 

In most cases, you have a few options, depending on the source and target combination regarding migration tools. This table summarizes the options available to migrate on-premises databases to Azure. 

SQL Server as a source has the most migration options, both cloud-based and on-premise. This is particularly true when migrating to SQL Server hosted on a virtual machine – which is essentially the same as any server to server migration. 

Microsoft SQL Server Migration Assistant, another downloadable migration tool, comes in several versions, each dedicated to migrating a specific database engine. There are versions for migrating from Access, DB2, MySql, Oracle, and SAP ASE.

Currently, there are no specific Azure MariaDB migration tools, but as MariaDB is very closely related to MySql, using MySql tools, either Azure-based or third-party have a more than even chance of working.

Azure Database Migration Guides is a portal to extensive documentation, describing step-by-step migration procedures for a multitude of scenarios.