Cloud migration step by step: how to plan your strategy and carry it out securely?

Cloud migration does not start with choosing AWS, Microsoft Azure or Google Cloud. First, an organisation needs to determine why it wants to change its current environment, which applications are actually worth moving and which model makes sense in terms of cost, security and future development.

A well-planned migration combines business and technology perspectives. It involves assessing the current infrastructure, classifying applications, selecting the right strategy for individual systems, preparing the architecture, security and integrations, and then testing, cutover and stabilisation. It does not end when the final application goes live in the cloud. The next stage is cost control, governance, monitoring and further modernisation.

When does cloud migration make sense – and do you need to move everything?

Just because an application can run in the cloud does not mean it should be moved there. The starting point should be a specific business problem or organisational objective.

What problems can justify cloud migration?

One signal is infrastructure that is becoming increasingly difficult to scale with the business. Expanding on-premises servers requires further investment, while preparing an environment for a new application takes too long. In this situation, more flexible resource scaling can deliver direct business value.

Another reason may be growing technical debt. Older systems require more and more effort to maintain, update and secure, while their limitations start to restrict the organisation’s ability to introduce new services.

Other factors that may lead to a migration decision include:

• the need to replace ageing infrastructure;
• difficulties scaling computing capacity;
• the need to provision test and production environments more quickly;
• availability and business continuity requirements;
• applications with dynamically changing resource requirements;
• the need to rationalise infrastructure after acquisitions or years of incremental expansion.

When assessing the economics of migration, TCO – Total Cost of Ownership is a useful measure. It includes not only the cost of purchasing servers or the monthly cloud bill, but also maintenance, energy, licences, administration, security, hardware replacement and the time your team spends managing the environment.

Only by comparing these elements can an organisation determine which model is likely to be more advantageous.

Full migration, a hybrid model or keeping some systems on-premises?

Cloud migration does not have to mean moving the entire infrastructure.

In a large organisation, a hybrid model is often more practical. Some applications may run in the public cloud, others may remain on-premises, while others can be replaced with SaaS solutions.

The decision to keep a particular system outside the public cloud may be influenced by factors such as very low latency requirements, close integration with local infrastructure, regulatory requirements, the nature of the data being processed or simply economics.

The best model is not the one that moves the most to the cloud. It is the one that best matches the organisation’s actual requirements.

Where should cloud migration start? Environment assessment and readiness

Before designing the target architecture, you need to understand the starting point.

This is one stage that should not be rushed. A missed dependency between applications or underestimated data volumes can later affect the schedule, costs or system behaviour after migration.

Inventory of applications, data and infrastructure

The first step is to organise the knowledge about the current environment.

The assessment should cover, among other things:

• applications and business systems;
• databases;
• servers and storage;
• networking and external connections;
• integrations and APIs;
• licences;
• dependencies between systems;
• performance and availability requirements;
• security mechanisms, backup and data recovery.

The goal is not to create an extensive hardware catalogue. The key is to understand dependencies.

An application may appear straightforward to migrate until it turns out that it communicates with several local databases, relies on an older authentication mechanism and exchanges data with a system that will remain on-premises for the next few years.

These details should be identified before migration design begins, not while switching over a production system.

How should applications be assessed for migration?

Not all workloads – applications and computing workloads operating within the IT environment – should be given the same priority.

For each one, it is worth assessing:

• importance to key business processes;
• technical complexity;
• dependencies on other systems;
• required level of availability;
• the type of data being processed;
• security and compliance requirements;
• current operating costs;
• modernisation potential;
• potential benefits of using cloud services.

The result is a map that helps answer three separate questions: what to migrate, when to migrate it and how to do it.

This is a much better starting point than trying to apply one strategy to the entire infrastructure.

Business case and success criteria

At this stage, the IT perspective needs to meet the business perspective.

If the reason for migration is cost reduction, you need to establish a baseline and define how costs will be measured later. If the objective is to provision new environments faster, it is worth documenting the current lead time and the expected improvement. If availability is the priority, measurable requirements for system operation are needed.

The business case may therefore include:

• TCO;
• forecast migration costs;
• the expected cost model after implementation;
• performance requirements;
• SLA;
• security and business continuity requirements;
• metrics that will be used to evaluate project success.

Only then can technology choices be grounded in the organisation’s actual needs.

How do you choose the right cloud migration strategy?

“Cloud migration” can mean several very different things. One application may be moved with almost no changes, another partially adapted to the new environment, while another may need to be rebuilt or replaced with a ready-made SaaS solution.

That is why the strategy should be selected for each application, rather than for the organisation as a whole.

Do not choose one strategy for the entire organisation

For example, an application whose infrastructure needs to be replaced quickly may first be moved using a rehost approach. A strategically important system may be rebuilt for a cloud-native architecture. An older HR application may be replaced with SaaS, while a system closely tied to local production infrastructure may remain in its current environment.

This approach allows a large transformation programme to be divided into decisions about individual systems.

It is also less vulnerable to technology hype. Cloud is a tool. If it does not solve a meaningful problem for a particular application, simply moving that application will change very little.

Cloud migration step by step – from target architecture to go-live

Once the assessment has been completed and a strategy assigned to individual applications, the migration programme itself can begin.

Step 1. Design the target environment

The target architecture should address questions such as:

• the chosen cloud model;
• provider or providers;
• data processing regions;
• networking and communication with other systems;
• identity and access management;
• data storage;
• backup and Disaster Recovery;
• monitoring;
• security policies;
• governance.

This is also the point at which you decide how the system will work with components that are not being migrated.

In a hybrid environment, the quality of these connections can be just as important as the cloud infrastructure itself.

Step 2. Prepare the environment and integrations

Before migrating an application, its target environment needs to be prepared.

This includes configuring networking, access, event logging, monitoring and the services the application will use. At the same time, integrations with systems remaining outside the cloud need to be planned.

Older solutions require particular attention. Replacing them is not always necessary. A better approach is often gradual modernisation and designing integrations in a way that allows the new environment to operate alongside legacy systems without disrupting day-to-day operations.

Step 3. Test your assumptions on a limited scale

In more complex projects, a pilot or Proof of Concept can be a useful step.

It does not need to be part of every migration programme. It is useful when there is meaningful uncertainty around performance, compatibility, integrations or the use of a specific service.

The test can be performed on a lower-criticality application or a representative part of the environment.

The objective is not to create an impressive demonstration. A pilot should answer specific technical and business questions before the project is scaled up.

Step 4. Migrate in waves

Trying to move the entire infrastructure at once increases the number of dependencies that need to be controlled at the same time.

A wave-based migration allows the programme to be divided into logical groups of systems. The order can be based on criticality, dependencies, complexity and risk.

Simpler applications can be used to validate the process. Critical systems can be migrated later, using lessons learned from earlier stages.

It is important not to separate applications artificially when they are strongly interdependent. Technically, they may be two systems, but from a migration perspective they form one ecosystem.

Step 5. Test before cutover

Once an application has been migrated, it is not enough to check whether it starts.

Testing should cover, among other things:

• business functionality;
• performance;
• integrations;
• user access;
• data correctness and integrity;
• security mechanisms;
• backup and recovery;
• monitoring and alerts.

For systems that require traffic to be switched over, it is worth preparing a cutover plan in advance, together with the conditions that would trigger a rollback.

This reduces the need for improvisation at a point when every minute can matter.

Step 6. Stabilise the environment

Production go-live does not mean the project is finished.

The first period after migration should be used to observe how the application behaves under real operating conditions. Performance, errors, load, availability and costs should all be monitored.

This is also the right time to compare actual results with the assumptions set out in the business case.

Once the new environment is stable, the organisation can move on to optimisation and further modernisation.

How do you secure data and maintain business continuity during migration?

Security should be part of the architecture from the beginning of the project. Adding it only shortly before production go-live usually means revisiting decisions made much earlier.

Protecting data during migration

A core set of controls includes:

• encrypting data in transit and at rest;
• identity and access management;
• the principle of least privilege;
• multi-factor authentication where required;
• event logging;
• security monitoring;
• backups;
• testing data recovery capabilities.

IAM – Identity and Access Management is particularly important. Expanding a cloud environment without clear rules for granting permissions can eventually make it difficult to determine who has access to which system and why.

Roles and responsibilities should therefore be designed together with the environment itself.

RTO, RPO and the rollback plan

Two parameters help turn the general expectation that “the system must work” into specific architectural requirements.

RTO – Recovery Time Objective defines the maximum acceptable time required to restore service after a failure.

RPO – Recovery Point Objective defines the maximum acceptable amount of data loss measured in time.

A system that can be unavailable for several hours requires a different approach from a platform where any extended interruption affects critical business processes.

RTO and RPO therefore influence backup policies, replication, high-availability architecture and the Disaster Recovery plan. They should also be reflected in the migration scenario and any rollback plan.

Compliance and data location

Technical security is only part of the requirement.

The organisation should also determine:

• what data will be processed in the environment;
• where it may be stored;
• who may have access to it;
• which regulations apply to the relevant process or industry;
• which internal security policies must be maintained.

For personal data, the requirements of the GDPR must be taken into account. Regulated organisations may have additional obligations relating to matters such as data location, access, business continuity or oversight of suppliers.

The security model should therefore be tailored to the specific environment rather than copied from a universal template.

What happens after migration? Costs, governance and cloud environment development

Migration changes where infrastructure runs. On its own, however, it does not solve the challenges of managing IT.

A poorly managed cloud environment can quickly become another complex environment – simply billed in a different way.

FinOps – controlling costs after migration

The pay-as-you-go model allows costs to be aligned with service usage. It provides flexibility, but it does not automatically optimise costs.

If teams can easily launch new environments, they can just as easily leave resources running after they are no longer needed. The same problem occurs when instance sizes are selected “just in case” or test environments run around the clock.

FinOps brings together technical, business and financial perspectives around cloud costs. In practice, this includes:

• monitoring utilisation;
• rightsizing, meaning adjusting resource size to actual workload;
• budgets and alerts;
• switching off unused environments;
• allocating costs to services, projects or owners;
• regularly reviewing whether the way the cloud is being used still matches business needs.

This makes cost part of architectural management rather than a surprise on the invoice.

Cloud governance and responsibilities

As the environment scales, clear rules become increasingly important.

Who can create new resources? How should they be configured? Who approves exceptions? How should resources be tagged so their costs can be allocated? Who is responsible for updates, security and monitoring?

Without such rules, a cloud environment can start developing in multiple directions.

That is why a cloud operating model should define responsibilities, governance, security and cost control. This allows the environment to scale without losing control over it.

Monitoring and observability

After migration, monitoring should not be limited to answering the question: “Is the application running?”

In distributed environments, the source of a problem may be the application, database, network, an external API or a cloud service.

Observability helps teams understand why a system is behaving in a particular way.

It is therefore worth analysing:

• availability;
• performance;
• errors;
• application behaviour;
• dependencies between services;
• resource utilisation;
• costs.

Good visibility into the environment shortens the path from detecting a problem to identifying its root cause.

Migration can be the beginning of modernisation

Not every application needs to be rebuilt before migration.

A practical path may instead look like this:

rehost → stabilisation → replatform or refactor → automation → greater use of cloud-native architecture.

This makes it possible to spread change over time and reduce the number of risks that need to be managed simultaneously.

At the next stage, the organisation can develop containerisation, Infrastructure as Code, CI/CD, platform engineering and operational automation. At that point, the cloud stops being simply another place to run servers and starts to change how applications are built and maintained.

How do you choose a cloud migration partner?

A good migration partner should be able to look beyond simply moving infrastructure.

It is worth checking whether they can support the organisation across several areas:

1. Business – linking technology to objectives, TCO and priorities.
2. Architecture – designing the target environment and integrations.
3. Migration – planning sequencing, testing, cutover and stabilisation.
4. Security – addressing identity, data protection and compliance requirements.
5. Operations – helping to organise governance, monitoring, costs and post-migration development.

Experience across different platforms also matters. If a project is tied to one provider from the outset simply because the partner works exclusively with that technology, architectural decisions may not be driven by the organisation’s actual needs.

It is therefore worth considering:

• expertise in AWS, Microsoft Azure and Google Cloud Platform;
• a vendor-agnostic approach;
• experience with hybrid and multi-cloud environments;
• their approach to legacy systems;
• the ability to carry out an assessment before implementation;
• expertise in subsequent maintenance and modernisation;
• how knowledge is transferred to the client’s team.

A partner should help the organisation make the right decisions even when the answer is not “move everything”.

Frequently asked questions about cloud migration