SQL Server on Azure VM vs AWS RDS

Compare Azure VM vs AWR RDS

Features

SQL Server on Azure VM

AWS RDS for SQL Server

Deployment

User deploys an Azure VM (with a SQL image if desired) – similar to EC2, quick to create but you manage SQL setup.

Launch via AWS console by selecting SQL edition/size – automated provisioning in minutes, no OS install needed.

Management

Self-managed, though Azure offers a VM extension for automating SQL patching/backups.

Fully managed by AWS – automated backups, patching during maintenance windows.

Customization

Maximum – complete OS and SQL control, legacy versions supported.

Somewhat limited – no OS access, must use parameter groups for tuning; many but not all SQL features availableSomewhat limited – no OS access, must use parameter groups for tuning; many but not all SQL features available.

Use Case

When full control is needed in Azure (legacy apps, custom integrations, SSRS/SSAS); a bridge between on-prem and cloud with control.

Great for simplifying DB management in AWS for standard workloads – companies that want cloud automation and can live within RDS feature limits (trading some flexibility for ease).

Maintenance Responsibility

You/your team – unless using Azure’s IaaS Agent to auto-patch, you handle updates.

Amazon – AWS applies SQL patches during set maintenance windows (or automatic minor version upgrades).

Operational Control

Full control – you can even remote desktop to OS and change anything.

Partial – you get an admin account but not full sysadmin; certain procedures and settings are blocked for stability.

Backups

User-managed (can use Azure Backup or SQL Agent jobs, or enable the SQL VM backup extension for Azure-managed backups)

Automated: daily snapshots + log backups (PITR up to 35 days) are handled by AWS; you can also take manual snapshots for longer retention.

Scalability

Vertical: change VM size (reboot required); Horizontal: add more VMs (e.g., Always On AG for read scale) – manual setup.

Vertical: modify instance class (reboot); Horizontal: Read Replicas (for Enterprise) allow up to 5 read-only copies (including cross-region); no horizontal write scaling (one primary).

Performance

High (depends on chosen VM and disks): you can use Premium SSD/Ultra Disk on Azure VMs and optimize like on-prem – performance is as good as the hardware allows, with full control.

Strong performance for most workloads but with some cloud overhead: RDS uses EBS storage (e.g., gp3 or io2 volumes up to 64k+ IOPS), and you can choose instance types with more memory/CPU. Very large workloads or those needing special hardware (like NVMe) might not fit in RDS’s offerings as of now.

Elasticity

No native auto-scale – you set a VM size; possible to script something with Azure Automation to scale VMs on a schedule or metric, but it’s user-implemented.

No automatic compute scaling – the instance class is fixed. RDS does support auto storage increase, so storage can grow with usage. For compute, one could use AWS Application Auto Scaling for RDS in some cases to trigger a bigger instance on schedule, but it involves a reboot – so essentially not seamless auto-scale.

SQL Server Version

Any version (since you control the install media). Azure marketplace images cover currently supported versions (2012+), but you could bring older versions on a custom image if absolutely needed.

RDS supports multiple SQL Server versions (as of 2023, versions 2012, 2014, 2016, 2017, 2019, and now 2022 are available on RDS) – you choose a major version when launching, and AWS handles the minor version patching. However, older versions eventually get deprecated for new instances.

SQL Feature Support

All on-box features supported – you can install SSRS on the VM, use SSIS, enable ML Services, etc., just as on a normal server. No limitations beyond what SQL Server normally has.

Most SQL Server features are supported, but RDS lacks extensibility: no FILESTREAM, PolyBase, ML Services, CLR (2017+), or xp_cmdshell. Some server-level settings can’t be changed after launch.

Cross-Database Queries

Yes, within the SQL instance on that VM you can do cross-database joins/transactions.

Yes, if multiple databases are on the same RDS instance, you can cross-query them. You cannot cross-query between different RDS instances directly (no official linked server support for cross-instance, since you lack sysadmin to configure it, though heterogeneous links might be possible in some cases with limitations).

Custom Software

Yes – you can treat it like any Windows server: for example, install Splunk forwarders, custom performance collectors, or even run other apps on the same VM (if resources allow).

No – cannot access the OS. Even enabling certain SQL features that require custom action is not possible. For example, you cannot install a custom certificate for SQL Server at the OS level (RDS manages the certificates). You rely on what AWS provides out-of-box.

Network Configuration

Runs in Azure VNet – full control over IP address, subnet, NSGs, etc., like any VM. You can even place multiple VMs in the same subnet for cluster setups. Connect via ExpressRoute/VPN to on-prem easily.

Deployed in your AWS VPC – you choose subnet group (which maps to subnets in different AZs for Multi-AZ). Usually kept in a private subnet; you control access via security groups and route tables. Option for a public endpoint exists (mainly for development or if you have no VPN).

Security

Similar to EC2: you manage OS hardening, patches, SQL security config. Azure can encrypt disks by default, and you can use Azure Key Vault for TDE keys. Azure VM itself is an isolated environment you control. Compliance again is on how you set it up (Azure just provides infrastructure that can be compliant if you configure it so).

RDS encrypts data, logs, and backups using AWS KMS, supports SSL for in-transit encryption, and integrates with AWS Directory Service for Windows Authentication. AWS manages OS security patching, and RDS meets compliance standards like SOC1 and PCI DSS.

Authentication

Windows Auth and SQL Auth supported – join the VM to a domain (on-prem AD or Azure AD Domain Services) and you get integrated security. You can also use contained database users, etc., just like on-prem.

Supports SQL authentication and Windows Authentication via AWS Managed Microsoft AD, allowing domain-joined AD users to log in. Does not support Azure AD or IAM authentication for SQL Server.

High Availability

Must be configured by user – e.g., Always On AG across VMs or a Failover Cluster with Azure Shared Disks or Azure FSx for SMB. Azure provides multi-AZ (multi-zone) VM placement for resilience, but SQL HA is your responsibility.

RDS Multi-AZ maintains a synchronous standby replica in another AZ, enabling automatic failover (30-60s) during outages. The application reconnects to the same endpoint seamlessly.

Disaster Recovery

User-defined: e.g., use Azure Site Recovery to replicate the VM to another region, or set up an AG with a replica in a secondary region for DR. Azure won’t auto-handle cross-region failover for VMs – your DR plan executes it.

RDS Enterprise Edition supports Cross-Region Read Replicas for DR and read scaling, but writes require manual promotion. Non-Enterprise users rely on manual snapshots for cold standby, as automated cross-region failover isn’t built-in.

Pricing

Pay for Azure VM + storage. E.g., ~$1.5-2k/month for 8 vCPU VM with SQL Std included. Using Hybrid Benefit (BYOL) might drop that to ~$1k (just VM). Azure RIs can save ~30%. Network egress (if any) is extra.

RDS for SQL Server charges hourly based on instance class, storage, and I/O. Pricing includes the SQL license, making it costlier than MySQL/Postgres. A db.m5.2xlarge (8 vCPU, 32GB) costs ~$3/hour, while Multi-AZ roughly doubles the price.

Licensing Model

License-Included or BYOL. Azure Hybrid Benefit lets you apply existing licenses; or pay-as-you-go includes SQL license. Per-second billing. Enterprise Agreement customers can also get dev/test pricing without SQL costs on Azure for non-prod.

RDS for SQL Server is License-Included only (except RDS Custom); BYOL is not supported. Costs include SQL Server CALs or per-core licensing, with discounts available via Reserved Instances (1-3 years). Express/Web editions are cheaper but limited.

Pricing Comparison of Database Configuration

8vCore + 4TB Data size + Backup,  Single Instance

~$1,700/month for 8 vCore GP Azure MI or SQL DB (license included);
~$1,500/month for Azure VM (license included) or ~$1,000 with BYOL.
On-prem ~$1k (Std) as above.

A db.m5.2xlarge (8 vCPU) RDS SQL Standard instance with 4TB General Purpose storage in US East costs $2.2k–$2.5k/month on-demand ($3.00–$3.50/hour), including the SQL license. Running the same on EC2 (BYOL) is cheaper but lacks RDS’s management benefits.

8vCore + 4TB Data size + Backup + DR/HA

HA requires a secondary VM (8 vCore + 4TB) but incurs no extra SQL Server license cost if using Azure Hybrid Benefit.
For DR, a geo-replicated secondary adds ~$1,800/month, bringing total costs to ~$3,400/month (excluding SQL license).
Backup adds ~$120/month. Without Azure Hybrid Benefit, SQL Server licensing adds ~$2,500/month, pushing total cost to ~$5,900/month.
DR and HA both require paying for full VM resources; SQL license charges apply to all nodes unless covered by Hybrid Benefit.

The same 8 vCPU Multi-AZ (HA enabled) instance costs $4.4k–$5k/month due to a standby replica. Adding a cross-region read replica increases the total to $7k+/month. Costs can be reduced with Reserved Instances or Standard edition instead of Enterprise.