Documenting a Cloud Migration: What to Capture Before, During, and After

Cloud migrations have a documentation problem that's different from most IT projects.

It's not that nothing gets written down. It's that a lot gets written down in the wrong places. Architecture decisions live in the architect's notes. Configuration choices live in someone's head. The "why" behind key decisions lives in a meeting that wasn't recorded.

Six months after a migration, when something breaks or needs to change, the team is often reverse-engineering decisions they made themselves.

Here's what to document, and when.

Before the migration: capture the baseline

You cannot document where you're going if you don't know where you started. Before anything moves, document the current state thoroughly enough that you could rebuild it if the migration went catastrophically wrong.

Current infrastructure inventory. Every server that's being migrated: hostname, OS, specs, role, dependencies. What does each server talk to? What talks to it? A server that nobody notices is a load balancer for three applications is going to cause an outage when it gets moved without those dependencies being accounted for.

Current application inventory. For each application: what it does, who uses it, what it depends on, and what depends on it. Pay particular attention to integration points and APIs between systems.

Current network topology. IP schemes, firewall rules, routing. You'll need this to design the equivalent in the cloud environment and to troubleshoot when something that worked on-premises doesn't work in the new environment.

Performance baselines. Response times, throughput, resource utilization for key systems. You need something to compare against after migration to know whether things got better or worse.

During the migration: document decisions as they happen

This is where most documentation debt accumulates.

Migration projects move fast. Decisions get made in calls and chat threads. Configuration choices get implemented without being recorded. By the time the project ends, the team can't fully reconstruct why the architecture looks the way it does.

The discipline that works: any significant decision gets a written record before the next phase starts. Not a long one. A few sentences is enough: what was decided, what was considered and rejected, and why.

Specific things to capture:

Architecture decisions. Why this cloud provider? Why this region? Why this instance type over others that were evaluated? Why this storage tier?

Network and security design. VPC/VNET structure, subnet design, security group or firewall rules. Document the intent behind the design, not just the configuration.

Service and licensing choices. Which managed services replaced on-premises equivalents? What licenses or subscriptions are in place? Where are accounts and credentials managed?

Configuration that deviates from defaults. Default settings exist for a reason. When you change them, document why. The non-default setting that nobody remembers changing is the one that causes the cryptic failure two years later.

Deferred items. Things that were planned for migration but postponed, deferred, or descoped. These become surprises if they're not tracked.

Cutover: the documentation that saves you

Cutover is when the pressure is highest and documentation discipline is lowest. This is backwards from what it should be.

Before cutover, write down:

The rollback procedure. If the cutover fails, exactly how do you revert? Who does what, in what order, and how long will it take? Write this before you need it.

The verification checklist. How will you know the cutover was successful? Specific systems, specific tests, specific expected outcomes. "Everything seems to be working" is not a verification.

The communication plan. Who gets notified at each stage? What's the escalation path if something goes wrong? What's the messaging to end users?

During cutover, track what actually happened versus what was planned. Deviations are important: they tell you whether the runbook needs updating and whether the new environment behaved as expected.

After the migration: close the loop

The post-migration period is when documentation debts get paid or become permanent.

Update the asset inventory. Everything that was migrated should be reflected in your current documentation. Decommissioned systems should be marked as such, not left in the active inventory.

Document the final state architecture. A diagram of what actually got built, not what was planned. These diverge during migrations and the plan often gets filed while the reality goes undocumented.

Capture the lessons. What was harder than expected? What wasn't documented well enough before the migration started? What would you do differently? This belongs in a post-project review document, not just in team memory.

Update runbooks. Any operational procedure that touched migrated systems needs to be reviewed and updated. Backup procedures, patching procedures, monitoring configurations, incident response playbooks.

Set a review date. Cloud environments change faster than on-premises environments. Set a calendar reminder for 90 days out to review whether the documentation still reflects reality.

The real cost of skipping this

Migration projects get declared done when the systems are running, not when the documentation is complete. This is understandable and wrong.

The documentation phase isn't overhead. It's the difference between a migration that permanently improves your operational capability and one that trades on-premises technical debt for cloud technical debt you don't fully understand.

The team that built it knows how it works. The team that inherits it six months from now doesn't, and may not be the same people. Document for them.