[DESIGNER] Notification service
Ref: System Design : Notification Service https://medium.com/@surfd1001/system-design-notification-service-d7a47fdfcee3
Architecting a Scalable Notification Service https://medium.com/swlh/architecting-a-scalable-notification-service-778c6fb3ac28
10 Best Push Notification Services & Tools [2021] https://www.mobiloud.com/blog/best-push-notification-services
Notification System Architecture https://medium.com/interviewnoodle/notification-system-architecture-e0d98ab3d18
A push notification server written in Go (Golang). https://github.com/appleboy/gorush