To understand why PHP is a suitable programming language for building microservices, we need to take a small peek into its history, where it comes from, which problems it was trying to solve, and the evolution of the language.
In 1994, Rasmus Lerdorf created what we can say was the first version of PHP. He built a small suite of Common Gateway Interfaces (CGIs) in the C programming language to maintain his personal web page. This suite of scripts was called Personal Home Page Tools, but it was more commonly referenced as PHP Tools.
Time passed and Rasmus rewrote and extended the suite so that it could work with web forms and have the ability to communicate with databases. This new implementation was called Personal Home Page/Forms Interpreter or PHP/FI and served as a framework upon which other developers could build dynamic web applications. In June 1995, the source code was opened to the public under the name of Personal Home Page Tools (PHP Tools) version 1.0, allowing developers from all over the world to use it, fix bugs and improve the suite.
The first idea around PHP/FI was not to create a new programming language, and Lerdorf let it grow organically, leading to some problems like the inconsistency of function names or their parameters. Sometimes the function names were the same as the low-level libraries that PHP was using.
In October 1995, Rasmus released a new rewrite of the code; this was the first release that was considered as an advanced scripting interface and PHP started to become the programming language that it is today.
As a language, PHP was designed to be very similar to C in structure so that it would be easier to be adopted by developers who were familiar with C, Perl, or similar languages. Along with the growth of the features of the language, the number of early adopters also began to grow. A Netcraft survey of May, 1998 indicated that nearly 60,000 domains had headers containing PHP (around 1% of the domains on the Internet at the time), which indicated that the hosting server had it installed.
One important point in PHP history was when Andi Gutmans and Zeev Suraski of Tel Aviv, Israel, joined the project in 1997. At this time, they did another complete rewrite of the parser and started the development of a new and independent programming language. This new language was named PHP, with the meaning becoming a recursive acronym---PHP (Hypertext Preprocessor).
The official release of PHP 3 was in June 1998, including a great number of features that made the language suitable for all kinds of projects. Some of the features included were a mature interface for multiple databases, support for multiple protocols and APIs, and the ease of extending the language itself. Among all the features, the most important ones were the inclusion of object-oriented programming and a more powerful and consistent language syntax.
Andi Gutmans and Zeev Suraski founded Zend Technologies and started the rewrite of PHP's core, creating the Zend Engine in 1999. Zend Technologies became the most important PHP company and the main contributor to the source code.
This was only the beginning and as years passed, PHP grew in features, language stability, maturity, and developer adoption.
Now that we have some historical background, we can focus on the main milestones achieved by PHP throughout the years. Each release increased the language stability and added more and more features.
PHP 4 was the first release, which included the Zend Engine. This engine increased the average performance of PHP. Along with the Zend Engine, PHP 4 included support for more web servers, HTTP sessions, output buffering, and increased security.
PHP 5 was released on July 13, 2004 using the Zend Engine II, which increased the language performance once again. This release included important improvements for object-oriented (OO) programming, making the language more flexible and robust. Now, users were able to choose between developing applications in a procedural or a stable OO way; they could have the best of both worlds. In this release, one of the most important extensions used to connect to data stores was also included---the PHP Data Objects (PDO) extension.
With PHP 5 becoming the most stable version in 2008, many open source projects started ending their support for PHP 4 in their new code.
This release was one of the most famous failures for PHP. The development of this major release started in 2005 but, in 2010, it was abandoned due to difficulties with the Unicode implementation. Not all the work was thrown away and most of the features, one of them being namespaces, were added to the previous releases.
As a side note, version 6 is generally associated with a failure in the tech world: PHP 6, Perl 6, and even MySQL 6 were never released.
This was a long awaited release---one release to rule them all and a release with performance levels seen never before.
On December 3, 2015, version 7.0.0 was released with the last Zend Engine available. The performance increase obtained only by changing the running version on your machine reached up to 70%, with a very small memory footprint.
The language also evolved, and PHP now had a better 64-bit support and a secure random number generator. Now you could create anonymous classes or define return types among other major changes.
This release became serious competition to the other so-called enterprise languages.
Like any programming language, PHP also has some disadvantages. Some of the most common mentioned disadvantages flagged are: security issues, unsuitable for large applications, and weak types. PHP started as a collection of CGIs and has become more modern and robust throughout the years, so it is pretty robust and flexible for a young programming language (in comparison with other languages).
In any case, an experienced developer will have no problem overcoming these disadvantages when building their application if they use the best practices.
As you can already see, the evolution of PHP was enormous. It has one of the most vibrant communities, was made for the web, and has all the power you need to create any kind of project. Without a doubt, PHP will be the right language for you to express your best ideas.