Modernizing Legacy Applications in PHP

Legacy PHP applications and runtime environments are present within many businesses, providing critical functionality and supporting essential processes. However, technology evolves quickly, and the older these systems become, the more difficult they are to maintain. Between employee turnover, lapsed documentation, and communication gaps between developer and administrator teams, many organizations are not even aware of how out-of-date their PHP has become until they attempt to modernize.

In this blog, I explore common challenges involved with modernizing legacy applications in PHP, including an in-depth exploration of a few key difficulties. I then highlight how professional support from trusted third parties can provide mentorship, supplement your team, and help you tackle your legacy PHP modernization projects.

Challenges in Legacy PHP Modernization

The Professional Services team at Zend modernizes PHP for a living. Over the years, we have observed an increasing trend of development teams not only lacking information about the runtime environment of their applications, but also lacking the awareness that this is an issue. For example, teams may not be aware of or have documentation on:

• The PHP version being run
• PHP/Apache/nginx modules
• php.ini configuration or its location
• Virtual hosts and other configurations
• Database or external service access rules (including networking)
• System packages and their versions
• And many other aspects

All these development teams know is that their system works, and nobody has touched it in years – even decades. However, once they partner with Zend for an upgrade or modernization project, all these issues come to the surface. For instance, in one project, issues related to the runtime environment accounted for over 90% of the problems in need of addressing.

Legacy PHP Modernization: Discovering the Runtime Environment

Before beginning a legacy PHP modernization project, you must complete a discovery of the runtime environment. Ideally, this journey would start with a bare-bones server. You can go with a container, but that just adds another layer of unknowns, especially when it comes to networking and security policies. It is better to save containers for later. The server would have the original PHP version with the original code, which we know to be compatible with that version. This way, the code isn't likely to be at fault.

Step One: Separating Environment From Code

The first step for any team looking to modernize legacy PHP is testing. You must test your application in a new runtime environment to discover what the code expects. A common mistake is to test both the upgraded code and the environment at once. This is a recipe for spending much more time debugging than when the concerns are separated.

Step Two: Identifying and Diagnosing Issues

Your team can then work through the issues one by one until the application shows no regressions. For example, this is where you may learn that a single sign-on integration needs to be reconfigured for each server that will initiate sign-ons. That has nothing to do with the code or the server, yet is part of the runtime environment.

Step Three: Documentation

Everything you learn needs to be documented. With that clear checklist, you can set up another server with the new PHP version. At that point, almost every issue should be due to PHP compatibility. After that is done, containerization becomes a more viable option, and the same methodology applies: work through runtime issues until all are resolved.

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Modernizing Legacy Applications in PHP: Basic Checklist for Discovering the Runtime Environment

Earlier, I mentioned a few common issues in modernizing legacy applications in PHP. These include knowledge of the PHP version being used, PHP modules and INI, and others. However, note that no two legacy PHP applications are exactly alike, and this checklist is by no means exhaustive. It simply represents a few common challenges that you will encounter during your modernization process.

Verify the PHP Version

The PHP version can be obtained from the production server by running php -v on the command-line. You must run the exact same version, not just PHP 5.3.X, for example. For instance, we were once given the wrong version, which made the code crash on a server but not locally. We can avoid this outcome by verifying the information.

Inventory PHP Modules and Configuration

Not only does your team need a list of modules, but also the configuration for each. This information will be in php -i in the command-line, or phpinfo() in a PHP script. This can lead to additional requirements, such as a configuration file for ODBC drivers, which isn’t part of the PHP configuration itself.

Simply replicating everything is the safest course of action, except for any INI directives that were removed in the new PHP version. However, when your development team has robust enough testing, this could be an opportunity to keep only what is needed. The old PHP configuration then becomes a mere reference when the application crashes or misbehaves.

Check Apache or Nginx Modules and Configuration

According to the 2025 PHP Landscape Report, Apache and nginx were the most popular web servers among PHP developers in 2025. My experience at Zend reflects these findings. However, your web server may differ. In any case, you will need to do the same as with the PHP itself: uncover and document all the modules and configuration that the application needs to run correctly.

Pay Attention to Databases and Services

Databases and services are likely the biggest headache in modernizing legacy applications in PHP, as they require cross-functional collaboration that often has a slow turnaround. Because these are runtime issues that can only be eliminated one at a time in sequence, any added delays can add up to months.

Examples of requests include, but are not limited to, whitelisting IP addresses, managing permissions on user profiles, and issuing certificates.

Ensure Compatibility System Packages

It’s useful to install the same versions of packages on your new systems as on the old systems when possible. Every package upgrade must be managed the same way as the PHP upgrade: one at a time to more easily debug regressions. For instance, I’ve seen an application crash because it didn’t like the new cURL version.

Address PHP Code

There are some cases where the code would be at fault, such as hardcoded IPs. Ideally, you would need to refactor the way the application manages its own configuration to be portable. For example, it may use an environment variable called ENVIRONMENT to determine.

Even if you don’t invest into making the application more server-agnostic, knowing what parts of the code need to be updated is valuable. Once you have the full list, this intermediate server has served its purpose of documenting the runtime environment. You can then configure as many new servers as you need with the PHP version you want. Even better would be if you can automate environment configuration with tools such as Puppet or Ansible.

On-Demand Webinar: Modernizing Legacy Web Apps

Join three open source experts in this recorded webinar as they explore tactics and strategies for modernizing legacy web applications in PHP and beyond.

Closing the Gap Between PHP Developers and System Administrators

Understanding the runtime environment of a PHP application is a cross-functional concern that will require someone sufficiently proficient in both development and system administration, which can be a steep ask for many organizations. This is where DevOps engineers are so valuable, but not all companies will have, or can afford, this dedicated role.

That's where Zend Professional Services can help. Our PHP experts are ready to rapidly develop modern, secure, and scalable solutions for teams pursuing PHP modernization projects. We also offer mentorship throughout your engagement with our services, providing your developers and administrators with the knowledge and skills required to maintain your modernized PHP applications.

Consultations for Modernizing Legacy Applications in PHP

If you are planning a PHP modernization project, engaging third-party consultation services from a trusted partner, like Zend, can go a long way in simplifying your journey. 

Throughout the process, we work with your team to test, diagnose, and modernize your legacy PHP. We also make sure that we understand your vision, business goals, and other requirements for your application. We provide mentorship and guidance to ensure you are equipped to run your system upon project completion. This can include working with both developers and system admins to ensure no communication gaps occur.

Learn more about Zend PHP Consulting Services >>

Flexible Black Belt Service Hours

With each passing year, PHP teams are asked to do more with less. If you are working with a tight budget or restricted developer time, then flexible service hours may be your best option. For instance, Zend Black Belt Services deliver the same renowned expertise, in-depth support, and excellent results as our traditional services, but delivered in smaller blocks of time for you to use as needed throughout your modernization process, allowing you to make the most of your resources.

Learn more about Black Belt PHP Services >>

Final Thoughts

The PHP runtime environment is often overlooked. It typically only becomes visible when trying to upgrade PHP code or when moving infrastructure. What is already a big effort is significantly exacerbated by a lack of understanding of the environment.

If you don't have the in-house PHP expertise needed, or if your developer and system admin time and energy is better spent on driving new business, third parties like Zend are here to help. We can provide mentorship for your team while documenting your environment and working on modernizing legacy applications in PHP. Not only will this prevent your next upgrade from being more difficult and time-consuming than it needs to be, but it will also allow you to spot opportunities to set yourself up for success in the future.

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Additional Resources

• Zend Container Registry
• White Paper - Planning Your Next PHP Migration
• White Paper - The Hidden Costs of PHP Upgrades
• Blog - PHP Exploitation: Can You Afford a Security Breach?
• Blog - PHP Upgrades: How to Plan and Execute Your Next Upgrade
• Blog - Best Practices for PHP Log Analysis