How to scale application from small to million of users

Big App consist of these components:

• Load Balancers: route request from each user to one of available servers.
• CDN: hosting static files like images, html, css, js files
• Web servers: scaling horizontal web servers to adapt a large amount of request from million users.
• Databases: This is another bottleneck of system. Scaling database is necessary for big system.
• Caches: This help to reduce work load of databases. Best cache strategy help make system fast.
• Message queue and Workers
• Logging, Metrics, Monitoring and Automation
• Datacenters: Global app should route user requests to nearest datacenter in geography location.