Migrating to AWS is no longer a technical decision. Today it’s a financial one. Over the last two years we’ve seen Peruvian companies move critical workloads to the cloud expecting to cut costs, only to end up paying 30% to 50% more than in their original data center during the first six months.

The reason? Almost never AWS. It’s the approach they took into the migration. These are the 7 most expensive mistakes we see in AWS migrations at Peruvian companies — and how to avoid them before you sign your first MAP.

1. Pure lift-and-shift with no assessment

The first instinct is “let’s move everything as-is and optimize later.” It sounds fast. In practice, poorly sized workloads on EC2 cost 2-3x more than on-premise because you pay for 24×7 usage without rightsizing having happened.

How to avoid it: a 2-3 week assessment before moving a single workload. Discovery, real sizing, identification of workloads that should NOT migrate, and a progressive modernization plan.

2. Not taking advantage of the AWS Migration Acceleration Program (MAP)

MAP funds up to 25-40% of your migration with AWS credits if you execute it with a certified partner. Many Peruvian companies migrate without accessing these credits because they don’t know they exist or don’t have the right partner.

How to avoid it: work with an AWS Migration Competency Partner from day 1. Caleidos holds this competency and runs MAP as a repeatable system.

3. Not designing the landing zone first

Jumping straight into “let’s just migrate” without AWS Control Tower, an organized multi-account setup, IAM with least-privilege, and a tagging policy is a time bomb. Three months later you have 50 untagged resources, you don’t know which account belongs to which business unit, and the bill is a mystery.

How to avoid it: invest 1-2 weeks in landing zone setup before the first workload. AWS Control Tower + Organizations + tagging strategy + cost allocation tags.

4. Underestimating data transfer

Egress costs (moving data out of AWS to the internet or between regions) tend to come as a surprise. A poorly designed architecture with services in different regions or constant calls to external APIs can add up to thousands of dollars per month in transfer.

How to avoid it: design the architecture taking into account service placement, VPC peering vs. internet gateway, and a CDN for static content. We model this in the initial assessment.

5. Not implementing FinOps from day 1

FinOps isn’t a post-migration project. It’s a continuous operating system: visibility → optimization → governance. If you start the migration without FinOps, in 6 months you have an uncontrolled bill and a team without the tools to understand it.

How to avoid it: implement AWS Cost Explorer + Budgets + Anomaly Detection + rigorous tags from day one. Consider tools like CAST.ai for autonomous optimization starting in the second month.

6. Ignoring progressive modernization

Pure lift-and-shift leaves most of the technical debt intact. Once on AWS, modernizing progressively (refactoring to containers, serverless, microservices where it applies) substantially reduces TCO.

A real production case: a Peruvian fintech migrated to AWS and, in parallel, built its Data Lake with AWS Glue + Athena + Redshift. Today they operate more efficiently than before the migration. The details are in the case studies section.

How to avoid it: a modernization plan by wave, post-migration. Don’t wait until everything is on AWS to start.

7. No post-migration operations plan

Migration doesn’t end at go-live. It ends when your team operates the new platform with confidence, or when a specialized partner does it for you with an SLA. Without an operations plan, what you migrated degrades within months.

How to avoid it: define from the initial plan how the migrated environment will be operated. Caleidos Lens© 24×7 covers this gap for many clients — it operates your AWS platform post-migration with FinOps + DevOps + AIOps + SecOps + Architecture integrated.

The recurring pattern

The 7 mistakes have something in common: they come from treating migration as a one-off event rather than a system. AWS rewards companies that understand that being in the cloud is a continuous practice, not a project that ends.

Are you planning an AWS migration at your company? Let’s talk before it starts. An early assessment costs less than fixing mistakes you’ve already made.