Choose direct cloud or hybrid based on continuity needs
Use a direct Google Cloud target for most public web apps. Reserve hybrid operation for real local dependencies, legal needs, or site-level latency needs.
Choose a primary Google Cloud US region when the app can place databases, uploads, and sessions in Google-managed services. This gives regional load balancing, autoscaling, backup tools, and a clearer recovery design than one colocation rack.
Keep an on-premises component during migration if the app needs factory systems, a local license server, or private directory access. Keep it when medical devices also require local access. A hybrid cloud setup spans local infrastructure and cloud services. It does not move everything at once.
The cloud design must match the app's real dependencies.
Pick a region pair before building
Use one primary region and one recovery region when RTO and RPO require coverage for a regional failure. RTO, or recovery time objective, is the longest acceptable time before service returns.
RPO, or recovery point objective, is the largest acceptable amount of lost data. Think of it as the maximum gap between your last safe copy and a failure.
For local workloads, Google Distributed Cloud can extend a consistent hybrid architecture to an on-premises site or edge location. Google Cloud remains the central control plane.
GKE Enterprise helps teams keep the same Kubernetes deployment patterns across cloud and local clusters. It also keeps policy controls, monitoring, and release steps consistent.
This model fits factory apps needing millisecond equipment access. It also fits regulated services with data sovereignty limits or air-gapped sites without constant internet access.
Google Distributed Cloud does not remove continuity planning work.
Local clusters still need version control, backup ownership, tested network boundaries, and a clear cloud failover choice. The common mistake is treating local Kubernetes as a passive extension of cloud operations.
Match the migration path to app dependencies
Choose rehosting, replatforming, refactoring, or hybrid operation based on app state, recovery needs, and dependencies. Do not choose only by virtual machine price.
| Path | Typical change time | Downtime risk | Best fit |
|---|
| Rehost | Days to 3 weeks | Medium | Stable VM app with few local dependencies |
| Replatform | 2 to 8 weeks | Low to medium | App that can use managed database, object storage, or containers |
| Refactor | 2 to 6 months | Lowest after completion | Growth app needing independent services and cloud-native scaling |
| Hybrid | 4 to 12 weeks | Depends on link and data design | Local systems or regulated data must remain active |
Rehost when the deadline is fixed
Rehost virtual machines when aging hardware must be retired before a lease, warranty, or capacity limit ends. Replicate servers and check their boot behavior.
Move IP-based services behind a load balancer. Remove local assumptions one at a time.
Replatforming moves selected layers into managed services without rewriting the whole app. It reduces the number of server-specific parts that can block failover.
Common changes include moving a self-managed database to Cloud SQL. Other changes include moving local uploads to object storage.
Move session data to a shared cache or database-backed session store. Web servers should not own data that users need after a traffic switch.
Cost the whole operating model
Compare total cost of ownership, not compute costs alone. Include cloud egress, load balancer processing, Cloud CDN, WAF rules, and backup storage.
Also include support, private connectivity, software licenses, monitoring, and staff time for the old environment. Parallel operation can create costs for several weeks.
The practical recommendation: Replatform stateful layers first. Then move web servers behind a global traffic layer. Rehosting makes sense when the deadline is tight. By itself, it does not create continuity until sessions, uploads, queues, and database writes have a shared tested design. Choose Google Distributed Cloud only for local latency, disconnection, sovereignty, or regulatory needs.
Use a phased plan to make the Google Cloud migration measurable. Do not treat cutover as one event.
During discovery, list app owners, dependencies, data classes, and continuity targets for each service. During foundation work, build identity, networking, monitoring, regional load balancing, and disaster recovery.
The replication phase can include Cloud SQL migration, object storage migration, and session-store migration. On-premises remains the write leader during this phase.
Then run a rehearsal with DNS cutover, controlled traffic ramping, and rollback tests before production. Track parallel-run costs, replication lag, open risks, and failover acceptance rules.
Retire the former environment only after stabilization is complete. This prevents a rushed shutdown from becoming an unplanned recovery test.
A safe migration moves state before it moves traffic. Replatform when state blocks recovery, but rehost when the deadline truly controls the decision.
Build traffic failover beyond a DNS switch
DNS is part of the production control plane. Cached records and uneven TTLs prevent DNS from giving fast, clean failover alone.
Use health checks that test real work
A health check is an automated request that decides if a server should receive traffic. A basic HTTP 200 check can pass while checkout or login fails.
Build one light endpoint for infrastructure health. Build one protected synthetic transaction for user health.
A synthetic transaction acts like a test user. It can log in, add an item, or verify a safe database read.
Keep sessions and files outside web nodes
Move session state out of local memory before canary traffic starts. Otherwise, users can lose logins when routing changes.
Place uploads in shared object storage or a replicated service. Define cache invalidation behavior before users reach both environments.
Check whether queues preserve message order or remove duplicate messages. The business process may need either behavior.
Put a controlled edge in front
Use Google Cloud Load Balancing, Cloudflare, or another global edge service for routing between on-premises and cloud origins. Add a CDN for static assets and a web application firewall for public traffic.
Set rate limits, check TLS certificates, and keep independent logs. A controlled edge gives one place to change traffic behavior.
Validate the site before calling hybrid connectivity production-ready. Measure normal and peak bandwidth for database replication, object migration, logs, image pulls, backups, and user traffic.
A link that handles daily requests may fail during initial data sync. It may also fail during a recovery event.
Use redundant network paths when recovery goals require them. Test routes in both directions.
Confirm that firewalls, proxy rules, DNS resolvers, IP allowlists, and MTU settings allow app and management traffic. MTU is the largest packet size a network path can carry.
If on-premises hardware stays in scope, document rack power, cooling, spare parts, and remote access steps. These checks stop healthy cloud services from failing through a lost local dependency.
Traffic control matters more than a DNS record alone. The next risk is harder: preventing two systems from accepting conflicting writes.
Control database writes during the cutover
A safe cutover has one authoritative write location at every moment. Replication cannot reliably fix conflicts after both systems accept writes.
Map every stateful component
Create a dependency sheet before the first migration test. List databases, user sessions, file uploads, caches, queues, and search indexes.
Also list cron jobs, payment webhooks, email relays, DNS records, IP allowlists, and third-party APIs. Small background jobs often create the most hidden write paths.
The most frequent error is forgetting a webhook or cron job. It can write old data after the cloud database becomes primary.
Run blue-green or canary routing
In blue-green deployment, both environments are ready, but one serves most users. In a canary deployment, a small user share reaches the new environment first.
That share is often 1% to 10%. Compare live behavior before you send more traffic.
- Replicate databases and files while on-premises remains the only write leader.
- Deploy the Google Cloud version and test it with read-only or masked production data.
- Send internal users, then 1% of public traffic, through the cloud path.
- Compare p95 latency, error rate, queue depth, login success, and replication lag.
- Freeze incompatible schema changes, promote cloud writes, and raise traffic in controlled steps.
Set rollback limits before go-live
Define stop conditions before changing traffic. Examples include error rates above the agreed limit or replication lag beyond the RPO.
Also stop for failed payment callbacks or failed synthetic login checks. Rollback is safest before the cloud becomes write leader.
Do not build an active-active or hybrid migration when a planned maintenance window is acceptable. Avoid it when traffic is low, state is not critical, or data redesign costs too much. Do not choose Google Distributed Cloud only because the app is local. Use it for real latency, disconnected operation, sovereignty, or regulatory needs.
One write leader makes rollback possible without guessing. The final proof is a timed recovery test with named owners.
Test continuity with RTO, RPO, and rollback drills
Launch only after a timed failover drill meets defined RTO and RPO targets. Run and pass a rollback test too.
Test the failures users actually notice
Simulate an on-premises origin outage and a Google Cloud origin outage. Also test broken database replication and expired TLS certificates.
Test DNS delay, failed background workers, and unavailable third-party APIs. Run every test while monitoring is active.
Record the time from alert to usable service. Users judge recovery by working pages, not by green server checks.
Set acceptance gates and named owners
Assign one cutover lead, database owner, traffic owner, security owner, and customer communication owner. Each person needs a clear decision scope.
The launch checklist must name the person who can stop the change. Naming only the people who can start it creates avoidable risk.
- A restore test proves backups can recover the required database point.
- A failover drill meets the published RTO and RPO.
- A rollback test restores the prior traffic path without data divergence.
- Health checks detect failed user transactions, not only running servers.
- Security controls meet applicable SOC 2, ISO/IEC 27001, HIPAA, PCI DSS, GDPR, or FedRAMP obligations.
A drill is useful only when it has a clock and pass criteria. These tests expose the gaps that diagrams and staging tests usually hide.
Frequently asked questions
Can I move an on-prem web app with no downtime?
You can avoid planned downtime by running both environments and shifting traffic gradually. This needs state replication, one active write leader, and tested rollback rules. DNS changes alone do not meet that standard.
How long does a Google Cloud migration take?
A small documented app often needs 3 to 7 days for basic preparation and testing. Apps with databases, file shares, compliance work, or legacy internal links often need 4 to 10 weeks.
What should I do if the GCP cutover fails?
Return traffic to the last verified healthy environment when only one side accepted writes. Stop the cutover and preserve logs and replication status. Reconcile data before any second traffic switch.
Is Google Distributed Cloud required for hybrid operation?
Google Distributed Cloud is not required for most hybrid migrations. Use it when local processing, disconnected operation, data sovereignty, or strict latency needs justify added operating costs.
How do I know users are seeing cutover downtime?
Watch synthetic user checks, p95 latency, 5xx errors, login failures, and support reports from separate networks. A successful DNS update can still leave users on the old path. Cached records can last minutes or hours.
Make the move only after recovery is proven
A cloud migration is ready when traffic can move independently and data has one clear owner. Your team must also reverse the change without guessing.
Start with a direct Google Cloud target for most public apps. Replatform stateful services where possible.
Reserve hybrid operation or Google Distributed Cloud for hard local needs. Recovery proof should decide launch readiness, not confidence in the migration plan.
What matters most:- Move application state before adding more cloud web servers.
- Use health checks and traffic control beyond a DNS record change.
- Allow writes in one authoritative location during every cutover phase.
- Budget for parallel operation, connectivity, security, and recovery tests.
- Approve launch only after RTO, RPO, failover, and rollback drills pass.
For the next planning stage, compare cloud hosting for small businesses. Also review VPS versus cloud hosting and use a website migration checklist before scheduling production traffic changes.
