How to Fix Legacy SIS Calendar Errors Without Touching the Mainframe

Introduction

It started with a ticket queue that wouldn't drain. A mid-sized state university was drowning in 50+ "Calendar Not Syncing" tickets per week. Students on iOS 17 were reporting disappearing classes, battery drain warnings, and "Ghost Events" that refused to delete.

The culprit? A 20-year-old Banner SIS export that was technically functional but practically broken for modern mobile devices.

The "Invisible Crisis"

The university IT team was stuck between a rock and a hard place.

The Problem: The SIS vendor hadn't updated their iCalendar export logic since 2014.

The Constraint: Touching the mainframe code required a 6-month change control process.

The Result: A reliable "Friday Afternoon Panic" every time a student's iPhone entered a recursion loop trying to parse an invalid VTIMEZONE.

We call this Support Debt. The cost of manually fixing issues caused by legacy infrastructure that you aren't allowed to touch.

Diagnosis: The 1,142 Errors

We deployed the Lokr proxy in front of their existing feed URL. Within 300ms, our diagnostics engine identified 1,142 RFC violations across their 25,000 active student feeds.

1. The Recursion Trap

The most critical error wasn't a syntax bug. It was logic. The legacy feed allowed infinite recursion in `RRULE` (Recurring Rules) without an `UNTIL` date. Modern iOS parsers try to calculate "forever" and eat 100% of the CPU.

# Legacy SIS Export (Broken)
RRULE:FREQ=WEEKLY;BYDAY=MO,WE,FR

# Lokr Sanitized Output (Fixed)
RRULE:FREQ=WEEKLY;BYDAY=MO,WE,FR;UNTIL=20241220T235959Z

2. UID Collisions (The Ghost Maker)

RFC 5545 demands that every event have a globally unique identifier (`UID`). The SIS was recycling IDs from previous semesters. When a student added "CHEM 101" to their calendar, it silently overwrote last year's "BIO 101" history. Or worse, merged them into a single, undeletable ghost event.

Infrastructure Warning: Outlook and Apple Calendar cache events by UID. If you reuse IDs, you corrupt the local cache on the user's device. The only fix is often a full factory reset of the calendar database.

3. VTIMEZONE Injection

The feed relied on "Floating Time" (`DTSTART:20240901T090000`) instead of explicit timezone definitions. This works fine if the student is on campus. It fails catastrophically if they check their schedule while visiting family in a different time zone.

# Ambiguous Time (Broken)
DTSTART:20240901T090000

# Timezone-Locked (Fixed)
BEGIN:VTIMEZONE
TZID:America/New_York
DTSTART;TZID=America/New_York:20240901T090000

The Zero-Touch Fix

The university didn't have to patch Banner. They didn't have to write a single line of code. They simply updated the DNS record for `calendar.university.edu` to point to Lokr's edge network.

1. Ingest: We act as the authoritative proxy, pulling the dirty feed from the SIS.

2. Repair: Our engine applies 40+ sanitization rules in-flight (sub-100ms latency).

3. Deliver: The student receives a pristine, RFC-compliant stream.

Security Assurance: Lokr operates on a Zero-Persistence architecture. We process feeds in memory and stream the results. We do not store student schedules, names, or locations at rest. This structural compliance simplified the university's InfoSec review to a single afternoon.

The Results

One week after DNS switchover:

• Ticket Volume: Dropped by 90% (from ~50/week to <5/week).
• Battery Drain Reports: Eliminated.
• Support Costs: Saved ~$85,000/year in Tier 1 helpdesk time.

Your legacy infrastructure doesn't have to be a liability. You can modernize the output without touching the source.