Amazon RDS vs EC2

Compare Amazon RDS vs EC2

Features

AWS RDS for SQL Server

SQL Server on AWS EC2

Deployment

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

User deploys an EC2 VM and installs SQL (AWS provides pre-built SQL AMIs)– faster than on-prem, but manual SQL config required.

Management

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

Fully self-managed: you handle OS/SQL patches, backups, monitoring.

Customization

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.

Maximum – full OS control, any SQL version/settings, install any software.

Use Case

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).

When full control is needed in AWS (e.g., custom configurations or unsupported features) ; lift-and-shift with minimal cloud modifications.

Maintenance Responsibility

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

You/your DBAs – AWS doesn’t patch your EC2 instances or SQL (user schedules and applies updates).

Operational Control

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

Full sysadmin rights on SQL and admin on OS – complete freedom (and responsibility).

Backups

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

Must be set up by user (e.g., backup to S3 or EBS, or use AWS Backup service); automated backup = none by default.

Scalability

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).

Vertical: change EC2 instance type (manual, downtime); Horizontal: add more VMs and configure clustering or load splitting manually (no built-in auto-scale).

Performance

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.

Can be very high (depends on instance and EBS setup): e.g., EC2 with Provisioned IOPS SSD can hit tens of thousands of IOPS; you can tune everything (Storage cache, TempDB on instance store, etc.).

Elasticity

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.

No native auto-scaling – fixed resources unless manually changed; you’d need custom scripts or AWS Auto Scaling Groups (not typical for DB VMs) to simulate elasticity.

SQL Server Version

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.

Any version you want (you install it). AWS SQL AMIs typically offer 2016–2019 and now 2022, but you could install an older one manually if needed (not recommended, but possible).

SQL Feature Support

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.

All features supported – it’s a full SQL Server. (If Windows, features like SSRS/SSAS need separate installation but can be on the same VM or another.) No artificial restrictions – you can even enable unsupported stuff at your own risk.

Cross-Database Queries

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).

Yes, you can query across DBs on the same instance or use linked servers between instances – same as normal SQL.

Custom Software

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.

Yes – install anything on the VM (e.g., anti-virus, monitoring agents, custom CLR assemblies in SQL, etc.). You have OS access to do so.

Network Configuration

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).

Runs in AWS VPC – you control subnet placement, security groups, routing (it’s like any other VM). You can give it a public IP or keep it private. It integrates with on-prem via VPN/Direct Connect seamlessly.

Security

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.

You manage security: enable TDE if needed (with your own key or certificate), use AWS KMS for volume encryption (just a checkbox on EBS), configure Windows Firewall or AWS Security Groups. Compliance depends on your configuration – AWS provides baseline (e.g., you can use AWS Config/Audits, but it’s on you to implement security best practices).

Authentication

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.

Windows Auth (AD) and SQL Auth both supported – it’s just a normal SQL Server in a Windows environment. You’d typically join the EC2 to your domain to use integrated auth.

High Availability

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.

Must be configured by user (e.g., Always On AG across two EC2s in different AZs). EC2 itself can be put in an Auto-Recovery, but that’s infrastructure-level. True HA = you set up clustering or AG, which is complex but doable (Launch Wizard can assist).

Disaster Recovery

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.

User-defined: e.g., set up an async AG to a second region’s EC2, or do periodic backups to an offsite location and plan for restore. AWS doesn’t automatically replicate EC2-based SQL to another region – you must architect it.

Pricing

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.

Pay for EC2 VM + storage + bandwidth. E.g., $2.0k/month for an 8vCPU VM with SQL Std license. If BYOL, you pay cloud costs ($700) and use your own license (~$1.3k amortized) separately. Reserved Instances can cut EC2 cost ~30-50%.

Licensing Model

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.

License-Included or BYOL. Can use on-demand hourly (with Windows/SQL licensing bundled) or bring your own licenses (requires Software Assurance for mobility). BYOL on EC2 can run on Dedicated Hosts or via License Mobility on shared tenancy.

Pricing Comparison of Database Configuration

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

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.

~$2,000/month (license-included Std) for m5.2xlarge + 4TB gp3 on AWS.
BYOL could lower cost if you already own a license.
On-prem roughly equivalent ~$1k (Std) to $3k (Ent) when amortized, but cloud includes hardware + management overhead.

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

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.

EC2: ~$4,000/month for two instances (Multi-AZ).