What makes a ServiceNow customization upgrade-safe vs upgrade-hostile?
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2 hours ago
Many ServiceNow instances function well day to day but encounter issues during platform upgrades, including broken UI behavior, regressions, and unexpected functional changes.
From a ServiceNow platform perspective, what types of customizations are considered upgrade-safe versus upgrade-hostile, and how can teams reduce upgrade risk while still meeting business requirements?
Not all customizations carry the same upgrade risk. The key distinction is whether a customization extends the platform or overrides it.
Upgrade-Safe Customizations (Preferred)
These generally survive upgrades with minimal or no remediation:
UI Policies instead of Client Scripts where possible
Flow Designer instead of legacy Workflows
Business Rules with clear conditions and minimal scripting
Dictionary overrides (used sparingly and intentionally)
Script Includes (scoped, reusable, and well-documented)
OOTB extension points (states, choices, UI Actions marked as “Insert and stay”)
These approaches align with ServiceNow’s supported extension model and are less likely to conflict with new platform behavior.
Upgrade-Hostile Customizations (High Risk)
These commonly cause upgrade failures or regressions:
Overriding or modifying OOTB scripts directly
Heavy Client Script manipulation of form load and save behavior
Hard-coded sys_id references
Customizations that replicate OOTB logic instead of extending it
DOM manipulation or unsupported UI hacks
Changes made without update set tracking or documentation
These often break because they depend on internal behavior that changes between releases.
Common Upgrade Failure Patterns
Knowledge editor (TinyMCE) regressions
Form behavior breaking due to client script conflicts
Assignment logic failing after OOTB rule changes
Performance degradation from accumulated scripting
Best Practices to Reduce Upgrade Risk
Prefer configuration over customization
Audit client scripts and UI actions before every upgrade
Remove deprecated or unused custom code
Test upgrades with real production scenarios, not just happy paths
Document the business reason for every customization
Outcome
Instances that follow upgrade-safe patterns experience faster upgrades, fewer post-upgrade incidents, and lower long-term technical debt—while still meeting business needs.
