SharePoint On-Premises to Online Modernization — Migration Playbook & Custom Solution Rewrite Strategy
Modernizing SharePoint Server 2013, 2016, or 2019 to SharePoint Online is a 5-phase engagement, not a lift-and-shift. This is the EPC Group playbook refined across 6,500+ SharePoint implementations since Project Tahoe (2000).
Phase 1 — Discovery (Weeks 1-4)
Full source-tenant inventory: every site collection, subsite, list, library, custom solution, workflow, InfoPath form, term store, connected app, third-party integration.
Phase 2 — Custom solution triage + rewrite backlog (Weeks 5-10)
Every custom solution surfaces a triage decision:
- Archive — nobody has used it in 24+ months.
- Replace with no-code — native SharePoint list rules, Power Automate templates, Microsoft Lists automation.
- Rebuild — SPFx web parts / extensions, Power Platform, Azure Functions.
Phase 3 — Target-tenant governance foundation (Weeks 11-14)
The five-pillar governance framework (see /answers/sharepoint-online-governance-framework) deployed before the migration, not after. Sensitivity labels + DLP for Copilot + permission cleanup runbooks.
Phase 4 — Waved migration (Months 4-8)
5,000-user weekend waves. Rollback protocol per wave. Continuous mail flow and coexistence.
Phase 5 — Copilot readiness + decommissioning (Weeks 33-36)
Copilot Governance Attestation + source-tenant decommissioning runbook (license retirement, MX-record removal, DNS cleanup).
Frequently Asked Questions
Should we migrate SharePoint on-prem to SharePoint Online or Subscription Edition?
SharePoint Online for 90% of enterprise buyers. SharePoint Server Subscription Edition (SE) only when you have documented regulatory requirements that prevent cloud (some federal / defense workloads), custom code investments that cannot be rewritten in the migration timeline, or an on-premises data gravity that makes cloud impractical. Even in these cases, EPC Group typically recommends a hybrid target — SharePoint Online for collaboration + SharePoint SE for the regulated workload — with a bridge between the two.
What happens to our custom solutions (SPD workflows, farm solutions, sandbox solutions, InfoPath forms)?
None of them migrate as-is. (1) SharePoint Designer 2013 workflows died April 2, 2026 in SharePoint Online — they need Power Automate rebuild (see /answers/power-automate-rebuild-after-sp2013-workflow-retirement). (2) Farm solutions do not exist in SharePoint Online — anything server-side needs SPFx web parts / extensions, Power Platform, or Azure Functions. (3) Sandbox solutions are deprecated — same rebuild path as farm solutions. (4) InfoPath forms need PowerApps rebuild. Every custom solution surfaces a triage decision: archive (nobody uses it), replace with no-code (native SharePoint list rules / Power Automate templates), or rebuild (SPFx / Power Platform / Azure Functions).
What is the typical timeline for a mid-enterprise modernization?
Mid-enterprise (2,000-10,000 users, 200-500 site collections): 6-9 months end-to-end. Phase 1 discovery: 3-4 weeks. Phase 2 custom solution triage + rewrite backlog: 4-6 weeks. Phase 3 target-tenant governance foundation: 3-4 weeks (see /answers/sharepoint-online-governance-framework for the five pillars). Phase 4 waved migration: 3-5 months (5,000-user weekend waves). Phase 5 Copilot-readiness + decommissioning: 4-6 weeks. Large enterprise (10,000+ users) extends to 12-18 months.
What are the "gotchas" that blow up SharePoint modernizations?
(1) Permission drift — 10-15 years of ad-hoc SharePoint permission changes create a graph that is nearly impossible to map cleanly to SharePoint Online. Plan on 60-90 days of remediation, not a lift-and-shift. (2) Unmanaged records — old sites with 20 years of retention that must be preserved through the migration; this is an eDiscovery Premium legal-hold operation, not a data-copy operation. (3) Metadata columns nobody documented — content types + site columns built over a decade that only 3 people remember; require excavation from the departed original developers' teammates. (4) Third-party AvePoint / ShareGate / Sharegate license expirations mid-migration. (5) The Managed Metadata Service — term stores that must be re-hydrated in the target tenant.
How does Copilot readiness fit into a SharePoint modernization?
Copilot readiness is not a phase you bolt on at the end — it is architected in from day one. During the target-tenant governance foundation phase (Phase 3), EPC Group deploys the sensitivity label taxonomy, DLP for Copilot policies, and permission-cleanup runbooks with the assumption that Copilot will be enabled at cutover. The alternative — migrate SharePoint first, then retrofit governance for Copilot — creates the oversharing surface documented in /answers/copilot-oversharing-incident-response. Migrations done Copilot-first-in-mind avoid that surface entirely.
What does an EPC Group modernization engagement produce?
A 5-phase deliverable set (mid-enterprise 6-9 month engagement): (1) Full source-tenant inventory — every site, list, custom solution, workflow, InfoPath form, term store, connected app. (2) Custom solution triage decision per item (archive / replace / rebuild) + rebuild backlog scoped by developer effort. (3) Target-tenant governance foundation — sensitivity labels, DLP, five-pillar SharePoint governance. (4) Waved migration plan with 5,000-user weekend waves + rollback protocol. (5) Copilot-readiness attestation + source-tenant decommissioning runbook. Delivered by senior architects who have run this across 6,500+ SharePoint implementations since Project Tahoe (2000).
Talk to a senior architect
Email contact@epcgroup.net or call 888-381-9725.
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