Note
Licensing rules change and depend on your agreements. Use this post to prepare the right questions, and confirm the details with your Microsoft licensing partner or the current Product Terms.
1. Azure
Azure Hybrid Benefit (AHB) lets SQL Server core licences with Software Assurance (or qualifying subscription licences) pay only the base compute rate:
| Target | Conversion (vCore model) |
|---|---|
| Azure SQL DB / MI, General Purpose | 1 Enterprise core = 4 vCores; 1 Standard core = 1 vCore |
| Azure SQL DB / MI, Business Critical | 1 Enterprise core = 1 vCore |
| SQL Server on Azure VM | Core for core, same edition |
- 180-day dual use: during migration you can run licences both on-premises and in Azure.
- Turn AHB on per resource (
licenseType: BasePricefor Azure SQL,AHUBfor SQL VMs). Track usage centrally with the centrally managed AHB feature (scope-level licence assignment). - Free passive DR replica rights: one free passive secondary for HA and one for DR in Azure, with SA or AHB.
- Reserved capacity (1 or 3 years) cuts compute cost further; it's separate from AHB and stacks with it.
2. AWS
| Model | Where | Notes |
|---|---|---|
| License Included | RDS, EC2 (SQL AMIs) | Pay per hour; simplest; no SA needed |
| BYOL with License Mobility (needs SA) | EC2 shared tenancy | Submit the License Mobility verification form to Microsoft |
| BYOL on Dedicated Hosts | EC2 Dedicated Hosts | For licences without SA; Microsoft's 2019 rules limit this to licences bought before 1 Oct 2019 (check your case) |
| RDS Custom | BYOM / license included options | Check current options per edition |
Free passive failover rights with SA also apply on AWS under License Mobility (check your terms).
3. Reduce the licence count during migration
- Right-size first: many on-premises servers are licensed for cores they don't use (see the sizing post).
- Edition review: Standard edition covers up to 24 cores and 128 GB buffer pool, plus Basic AGs. Many apps don't need Enterprise.
- AWS Optimize CPUs: on EC2 you can disable hyperthreading or reduce vCPUs on memory-heavy instance types, so you license fewer cores while keeping the memory.
- Consolidate small databases onto fewer instances, or into elastic pools on Azure.
- Retire unused databases: no licence needed at all.
- Dev/test: use Developer edition (free) or dev/test pricing, never production licences.
4. Extended Security Updates (ESU)
SQL Server 2012 and 2014 are out of support. On Azure (VMs and Arc-enabled servers via pay-as-you-go ESU) security updates are available under Microsoft's ESU terms; on other clouds and on-premises you buy ESU. Use migration as the moment to upgrade the version instead.
5. A worked comparison
For each database, compare 3-year cost of: (a) AHB + reserved on Azure, (b) license included on AWS, (c) BYOL on AWS, (d) Babelfish (no SQL licence, but migration effort). Include support, HA replicas and backup storage. The cheapest option often changes when HA is included.
Tip
Keep a licence register that maps every cloud SQL resource to the licence it uses (AHB, BYOL or included). Auditors ask for exactly this, and it's painful to rebuild later.