Let’s be real - LinkedIn messaging used to suck. You’d get notifications that didn’t make sense. Messages showing up in weird places. That awkward moment when someone replies to a message you can’t even find. But after 2 years of work, the eng team finally cleaned up this hot mess. Here’s the inside story you won’t find in their press releases.
Old vs New - spot the difference!
The Hot Mess Era
Back in 2020, LinkedIn’s messaging was held together with duct tape:
- 3 different codebases for messages (why??)
- Notifications that sometimes... just didn’t notify
- Group chats that exploded if someone left
- Search? Forget about it
One engineer told me: “We had so many message types even we didn’t know how they worked.” Yikes.
The Breaking Point
Three things forced them to act:
1. Users complained about lost job offers (!!!)
2. Mobile app ratings tanked to 3.2 stars
3. New features took 6+ months to ship
Something had to give.
The Great Unification Project
The team attacked the problem on 3 fronts:
1. Killing Zombie Code
- Retired 15+ legacy message types
- Deleted 200k lines of obsolete code
- Standardized on Protobuf for all new messages
2. Notification Overhaul
- Built smart priority system (no more spam!)
- Added cross-device sync that actually works
- Created unified error handling (finally)
3. The Search Miracle
- Implemented Elasticsearch for messages
- Added filter by date/job/connection type
- Made search work across web & mobile
“We basically rebuilt the whole stack from scratch,” admitted a senior dev. “Scary as hell but worth it.”
Technical Nightmares They Faced
Some code snippets show the struggle:
// Old notification code (yikes)
function sendNotification(user) {
if (user.premium) { /* special case */ }
else if (user.mobile) { /* different logic */ }
else { /* ??? */ }
}
// New unified system
const NotificationSender = {
send: (user, message) => {
// Single code path
broker.publish('notifications', {user, message})
}
}
They cut notification code complexity by 80%. No wonder things work better now.
The Results
After launching the new system:
| Metric |
Improvement |
| Message delivery time |
2.3s → 0.4s |
| Notification errors |
-92% |
| Support tickets |
-65% |
App store ratings jumped to 4.6 stars. Turns out people like it when messages actually work!
Lessons Learned
- Legacy code is toxic: Better to rewrite than keep patching
- Users notice infrastructure: Bad backend = bad UX
- Mobile first isn’t enough: Must design for all platforms
As the eng director put it: “We learned that messaging isn’t a feature - it’s the whole damn product.”
What’s Next?
The team’s now working on:
- AI-powered message sorting
- End-to-end encryption (finally!)
- Cross-platform message editing
Read the full technical post: LinkedIn Engineering Blog
