Being an optimist I would say, Yes! Having worked on a large scale high visibility site I’ve personally seen it happen, so definitely Yes! When the budget was not a limiting factor, I saw vertical and horizontal scaling at it’s best. Get the biggest badest app server, then multiply that by 20 with multiple load balancers. CDN cache everything possible. Scaling solved. Millions of views, thousands of transactions per second no problem. The databases were actually starting to buckle from all the connections. Enter pgBouncer connection pooling and more load balancers, but that is the point. You can scale to the point where it isn’t a problem with code but infrastructure.
But what if you can’t. Here are my experiences.
You add more RAM, CPUs, faster pipes (fiber optics directly to another server or network), SSDs. This is all possible, as CPUs reach their limits this gets to be a limiting factor. This has a threshold. With more users, the server can still meltdown. This is not for an exponent growth more of a linear one.
This also holds true for the database server, as most issues are database related. Slow queries can run faster by beefing up the hardware it runs on.
I consider this a quick fix for linear or predictable growth.
Load Balancing! Get more servers to do the job. Two or twenty is better than one. Share the load between servers. This can and will get costly. Be it cloud or metal or a combination of the two. Horizontal scaling if done correctly can be a really easy solution to scaling issues.