What does it mean to "architect your infrastructure to support scaling", when referring to a PHP/MySQL application?

MVC is a design pattern. While it has nothing to do with how scalable your application is, using a framework (such as Yii) usually means you have much less things to worry about than someone not handling their database connection well. Scaling means to make your application's database layer able to handle multiple requests at a time. The more you can handle, the more scalable your application is. As an example, in Facebook, millions might be liking and commenting at once, which means lots of SELECT and INSERT queries are being run all at once. A scalable application is one that allows you to do various scaling methods (sharding for example) without the need to modify your application, because the underlying framework already supports it, or because you have specifically written such a code.

I know some people might call me a pedant, but I would say there was a difference between architecting your "infrastructure" (as the question asks) to support scaling and architecting your application to support scaling. Architecting your application would be making smart / efficient coding and database query optimization.  Architecting your architecture would be things like optimizing your storage (using appropriate storage, optimizing the path to storage, filesystem tuning) to remove bottlenecks, tuning databases, smart use of reverse proxies and caching, clustering your databases, use of (or at least planning around the use of) load balancers, and related concepts. It is an ambiguous question in that its specific meaning is dependent largely on what exactly the application is doing, but I think I've outlined the theme to any correct answer.

First off lets get some concepts cleared out. Performance issues: when your application is slow for a single user. Scalability issues: when your application is fast enough for a single user, but slows down when many users use it at the same time. Scaling up(vertically): when you add more resources to your application servers, eg. more CPU, memory, etc. Scalling out(horizontally): when you add more nodes to the system, eg. adding more servers If your application can accomodate growth by either scaling up or out, then you have a "scalable system". To answer the last part of your question, using MVC design pattern is directly related to the problem of scalability, it just makes your life as a developer lot easier. Using MVC frameworks like Laravel, CodeIgniter, Yii, etc. is beneficial because they provide a good database abstraction layer and also internally implement efficient handling of database connections, sessions and caching. How do you make your application scale ? There are a lot of things to it. You will have to take particular care while designing your application, database and infrastructure. These things are application and design specific. has provided a brilliant answer and covered most of the general points. A quick search will also get you lots of resources you can refer to.

Some more points.. 1. Keep your architecture simple. Don't add/use things which generate complexity. It'll give you more grip for rapid development & easy handling. 2. Try to use loose coupling technique. Ref google for advantages of " loose coupling technique". 3. Use standard practices(design patterns, OOP's) for writing efficient codes.

Efficient Coding . Less queries . Efficient Database design .

To me sounds like a boss is trying to protect their app from future over-success ;-) Allow me to offer a rather different answer: It means you can build your app in a way that is easier to scale in the future as opposed to building your app in a way that is harder to scale. This is not limited to Scaling though and one can say an app is built in a way that is easy to expand, make more secure, go mobile etc etc as opposed to an app that is built in such a way that makes it hard to got in any of the above directions. Now how exactly do we make a PHP/MySQL app that is easy to scale in the future ? Though it is possible to give some exact answers to that question, yet judging from your original question and my impression of your  understanding of MVC and stuff, I would tell you this (the Agile way, by the way, so no classical "Architecture" is involved): You should follow the very basic guidelines and best practices and just code the best way you can and don't think about Scalability yet. Just basic code quality stuff: Pick up a framework that makes it easy for you to code. Almost all of them are MVC so don't worry about it. We are using Laravel. Yii and Symphony are great too. Symphony is the Enterprise one but it is also the most complicated. Don't pick Drupal or Wordpress or any of the less OOP frameworks. Why? books could be composed to answer that but in short the OOP paradigm would in the long run serve you better in your goal of being Scalable (and in many other ways). Most certainly use TDD. The de-facto unit testing library for PHP is PHPUnit and all the frameworks above has integrations with it. Learn about Normal Forms and good database design. Make sure you understand the surrounding stuff: Primary Keys, Foreign Keys, Relations, Integrity, Anomalies etc etc. Not a deep, academic understanding. A good guts understanding is enough.  Also it serves well to learn ERD so you can better express your thoughts. Learn  about de-normalizations and why they come handy (this is important actually) Finally wrap your head around actual Scalability and Performance concepts: Profiling, Response-Time, Throughput, Concurrency (in the relevant contexts), Horizontal vs Vertical scaling. Load Balancing etc etc. Begin with Performance and then make your way towards Scalability. You ought not to do that in that particular order though. Do the above and you will figure out the rest.