AWS Cloud Migration: A Practical Guide for Businesses

Why businesses move to AWS, and when they shouldn't

The usual triggers are concrete: servers out of warranty, a data center or colocation contract up for renewal, a disaster-recovery plan nobody has tested, or a small IT team spending its week patching hardware. AWS turns hardware purchases into monthly spend, lets you add capacity in minutes for busy periods, and gives you managed databases, backups and monitoring you would otherwise build and babysit yourself.

The cloud is not automatically cheaper. A large, steady workload on hardware you already own, run by an experienced operations team, can cost more on AWS, especially if it is moved as-is and left running around the clock.

Licensing (Windows Server and SQL Server especially), latency to systems that stay on-premises, and data residency rules can also change the answer. A good plan says which workloads move, which get replaced and which stay put.

Step 1: Measure what you actually use

Collect at least two to four weeks of CPU, memory, disk and network data per server, and make sure the window includes your busiest days (month-end close, payroll, a seasonal peak). For a few servers a spreadsheet is enough; for larger estates, AWS offers the Application Discovery Service to collect data and Migration Evaluator to build a cost case.

Step 2: Choose a strategy for each workload (the 7 Rs)

AWS describes seven migration strategies. The right one depends on how valuable a system is, how much life it has left and how much change your team can absorb at once.

Most businesses rehost or replatform first, because it is fastest and lowest risk, and improve the systems that matter once they are running in AWS. If an application needs deeper work, see our guide to modernizing legacy .NET applications without starting over.

Step 3: Build the foundation before moving anything

A "landing zone" is the secure, organized AWS environment your workloads move into. Building it first avoids the most expensive kind of rework: fixing networking and permissions after production is already running on top of them.

• Identity: single sign-on through IAM Identity Center, multi-factor authentication for everyone, and the root user locked away with its own MFA device.
• Network: private subnets for databases and application servers, public subnets only for load balancers, and a site-to-site VPN (or AWS Direct Connect) if systems stay on-premises during the migration.
• Logging: CloudTrail in every account and alerts on root logins, IAM changes and security group changes.
• Backups: AWS Backup plans defined up front, with one restore actually tested before go-live.

Step 4: Move data and servers in waves

Pick a pilot that is useful but not critical, such as an internal wiki or a reporting tool, and run it through everything: replication, cutover, monitoring, backup restore and a rehearsed rollback. Write down every surprise. Then group the remaining systems into waves of applications that depend on each other.

How long will the data take to move?

Do this arithmetic early, because it decides the tooling. Moving 4 TB over a dedicated 200 Mbps link takes about 44 hours at full speed (4 TB × 8 = 32,000,000 megabits ÷ 200 Mbps ≈ 160,000 seconds); in practice plan for two to three days, which is fine for online transfer with AWS DataSync. 80 TB over the same link would take over five weeks, which is when a shipped AWS Snowball device makes sense.

• AWS Application Migration Service: replicates whole servers continuously into AWS, so the final switch takes minutes rather than a full copy.
• AWS Database Migration Service (DMS): copies a database and then keeps replicating ongoing changes until you cut over; add the Schema Conversion Tool if you are changing database engines.
• AWS DataSync and Snowball: move file shares online, or ship data on a physical device when the network is too slow.

Understanding the real costs

A realistic budget has two parts: what it costs to run on AWS every month, and what it costs to get there. The second part is the one people forget.

Data coming into AWS is free. Data going out to the internet is billed: at the time of writing, the first 100 GB a month is free and the next tier is about $0.09 per GB in US regions. A file-heavy application serving 5 TB a month to customers therefore adds roughly $450 a month in transfer alone, unless a CDN such as CloudFront sits in front of it.

Price everything in the AWS Pricing Calculator using the sizes from your measurements, not your current hardware specs. Larger migrations may qualify for AWS funding such as the Migration Acceleration Program, usually through an AWS partner. Once you are running, our guide to reducing AWS cloud costs covers keeping the bill under control.

Security: your half of the shared responsibility

AWS secures the data centers, hardware and underlying services. You secure everything you configure: accounts, permissions, networks, operating systems, applications and data. Almost every serious cloud incident lands on the customer's side of that line.

• Give each application its own IAM role with only the permissions it needs, and avoid long-lived access keys.
• Turn on Amazon S3 Block Public Access at the account level, so a single mistaken bucket setting cannot expose data.
• Encrypt data at rest with AWS KMS and in transit with TLS.
• Keep databases and application servers in private subnets; expose only a load balancer or CDN to the internet.
• Enable Amazon GuardDuty for threat detection and AWS Security Hub for configuration checks from day one.
• If you take card payments or hold regulated data, design for it from the start; our PCI compliance assistance covers this.

Cutover: keeping downtime to minutes

Downtime is mostly decided by how you move the data. Copying a 500 GB database during a maintenance window can take hours; replicating it continuously for days beforehand reduces the final switch to minutes.

Common migration mistakes

• No dependency map. A forgotten integration, often a scheduled job or a scanner sending email, fails after cutover.
• Copying server sizes 1:1. You pay every hour for headroom bought for five years of growth.
• Ignoring data transfer. Traffic leaving AWS, and between regions, is billed per gigabyte.
• One big-bang weekend. No room to learn, and nowhere to roll back to.
• Security added later. Retrofitting networks and permissions under live traffic is slow and risky.
• Untested backups. A backup you have never restored is a hope, not a plan.
• Stopping at lift-and-shift. The savings usually arrive with right-sizing and managed services after the move.