How do you go about upgrading an old PHP application

Before upgrading a legacy PHP application, there are a few essential preliminary considerations to make the upgrade process smoother and ensure it addresses your actual needs.

First, you need to decide if what you want is an actual upgrade, or if you want to build a completely new application and migrate the content from the old one.

Second, you have to define what an “upgrade” even means. Sometimes, an upgrade is only from the perspective of the code – for example, upgrading to a new version of PHP.

But is that the lowest level? Older versions may already be out of date, meaning that they are not supported and don't have any security patches. In my personal experience, older PHP versions are not as problematic as the apps themselves.

What do I mean by that? I mean that it’s more likely that an old app will have a security vulnerability which attackers are more likely to use as an attack vector than the PHP version. That's typically how we see things in our work with clients.

If a company has an old PHP app, it usually means it was built in the ages when PHP was quite wild. In that time, many of the people working on PHP websites weren't prioritizing features like security, which led to a lot of “hacky” solutions and spaghetti code.

So, if your main reason for upgrading is only about wanting a newer PHP version, then I would actually consider if an upgrade is even worth it. Bringing up a PHP version to a higher version means a lot of work in the code with ROI close to zero.

But if the upgrade is about making the application better and upgrading the user experience, i.e. an actual functional upgrade, then of course the upgrade needs to happen, or an entirely new application has to be built.

My point is that upgrading just for the sake of upgrading can be a very low-ROI activity because at the end of the day you spend a lot of time, energy and resources, and you end up with what’s practically the same application. Our first-hand experience tells us how value can be missed by upgrading for the wrong reasons.

If you want to improve security, for example, there are other more important things to do on the server and infrastructure level without needing to upgrade to a newer version. This can include measures such as putting the application under some kind of firewall so it's only accessible through VPN IP addresses, or adding an additional authentication level before the application.

Skipping the version update may sound like a dangerous proposition, but if that’s the only reason you want to update or upgrade an old PHP application, then I would definitely consider other options.

Upgrading an old PHP application

If you do decide that your old PHP application needs an upgrade, I recommend a structured, step-by-step approach:

1. Plan extensively

Start by scheduling extensive testing and breaking the upgrade process into manageable sprints. Planning helps avoid disruptions and reduces risk.

2. Test in a staging environment

Before upgrading production, thoroughly test in a staging environment using unit, integration, and end-to-end tests. Incremental testing catches issues early.

3. Upgrade PHP versions gradually

If you’re several versions behind, upgrade step-wise rather than doing a big jump in order to simplify debugging and issue resolution.

4. Update packages and libraries

Update all dependencies to versions compatible with the new PHP version to prevent package conflicts.

5. Containerize the application

Use Docker or a similar tool to manage different PHP versions easily and isolate environments.

6. Fix backward compatibility issues

Use automated tools like Rector to help modernize the codebase by fixing deprecated functions and syntax automatically.

7. Document everything

Keep clear documentation on discovered issues and solutions for easy replication.

8. Consider a rewrite if needed

As I already pointed out earlier, sometimes rewriting the app from scratch on a modern stack may be a better option if the legacy code is too outdated or fragile.

Conclusion

This kind of upgrade approach balances ensuring security, improving performance, and maintaining functionality while minimizing disruption and technical debt.

If your in-house PHP expertise is limited, it’s wise to partner with external PHP migration experts in order to ensure the upgrade process meets your needs and deliverables.

If this is the case, we can quickly provide you with proven PHP developers to help you with the upgrade; reach out to us and we’ll schedule a call.