Among the standard object oriented principles is favouring composition over inheritance, and there are plenty of design patterns that work along this line. However, one of the most useful day-to-day facets of the idea doesn't seem to get a lot of attention from PHP developers, namely dependency injection.

The general idea is, that if your class depends on some other object, that object should be passed in rather than generated internally or retrieved via a global variable or singleton.

One of the biggest benefits of PHP is how easy it is to find servers that run it. The near ubiquity of the LAMP stack among hosting providers does, however, lead to quite a common problem with inappropriate setups.

PHP programmers generally know what a good systems architecture should look like, but it is often a reality of development that they will have little input on the system itself until the last minute. In fact, it's far from uncommon for a developer to be faced with an off-the-shelf dedicated LAMP server, and left up to their own devices.

Recently, I've been working with a client as part of a major platform change they're making. It's the third time I've been involved with a big architecture shift, each at a different company, and each larger than the last, but there seem to be some observations that apply whether you've got five servers or five hundred.

1. Business carries on

It can be easy to get somewhat myopic when in the middle of an exciting architectural change. Major platform transitions tend to occur when there has been a realisation high up in the company that something needs to be done, so teams often have a fair degree of scope and freedom. However, it is even more likely that other parts of the business will need to continue to work on the existing system. If a new feature is required then it's going to get developed, even if that involves duplicating, or worse conflicting, with work that's being done as part of the platform change.