I've been in almost this exact same situation with a slightly smaller team and "only" about $5 million running through the tangled web of php.
We did a complete rewrite into a Django application, it took 2 years and untold political pain but was absolutely the correct choice. The legacy code was beyond saving and everyone on the team agreed with this assessment - meaning our political battles were only outward facing.
In order to get support, we started very small with it as a "20% project" for some of our engineers. After level setting auth, cicd, and infrastructure stuff, we began with one commonly used functionality and redirected the legacy php page to the new python-based page. Every sprint, in addition to all the firefighting we were doing, we'd make another stealth replacement of a legacy feature with its updated alternative.
Eventually we had enough evidence that the replacements were good (users impressed with responsiveness, upgraded UI stuff like replacing default buttons with bootstrap, etc.) that we got a blessing to make this a larger project. As the project succeeded piecemeal, we built more momentum and more wins until we had decent senior leadership backing.
Advocating for this change was basically the full time job of our non-technical team members for 2 straight years. We had good engineers quit, got into deeply frustrating fights with basically every department in the company and had rough go of it. In the end though, it did work out very well. Huge reduction in cost and complexity, ability to support really impactful stuff for the business with agility, and a ton of fulfilling dev experience for our engineers too.
All this is to say, I understand where everyone warning you not to do a rewrite is coming from. It's a deeply painful experience and not one to be embraced lightly. Your immediate leadership needs to genuinely believe in the effort and be willing to expend significant political capital on it. Your team also needs to be 100% on board.
If you can't make this happen and you're not working on a business which does immense social good and needs your support as a matter of charity, you should quit and go somewhere more comfortable.
It sounds to me like you did a full rewrite by replacing the app piece by piece, sprint by sprint, releasing changes quite often and bringing that value all the way to the user. I think that is really clever.
My impression from others in this thread is that they mean "start from scratch and build until features are on-par with current product" when they say full rewrite.
Your version of full rewrite seems like it is generally applicable, but I have very little faith in the latter approach.
We did a complete rewrite into a Django application, it took 2 years and untold political pain but was absolutely the correct choice. The legacy code was beyond saving and everyone on the team agreed with this assessment - meaning our political battles were only outward facing.
In order to get support, we started very small with it as a "20% project" for some of our engineers. After level setting auth, cicd, and infrastructure stuff, we began with one commonly used functionality and redirected the legacy php page to the new python-based page. Every sprint, in addition to all the firefighting we were doing, we'd make another stealth replacement of a legacy feature with its updated alternative.
Eventually we had enough evidence that the replacements were good (users impressed with responsiveness, upgraded UI stuff like replacing default buttons with bootstrap, etc.) that we got a blessing to make this a larger project. As the project succeeded piecemeal, we built more momentum and more wins until we had decent senior leadership backing.
Advocating for this change was basically the full time job of our non-technical team members for 2 straight years. We had good engineers quit, got into deeply frustrating fights with basically every department in the company and had rough go of it. In the end though, it did work out very well. Huge reduction in cost and complexity, ability to support really impactful stuff for the business with agility, and a ton of fulfilling dev experience for our engineers too.
All this is to say, I understand where everyone warning you not to do a rewrite is coming from. It's a deeply painful experience and not one to be embraced lightly. Your immediate leadership needs to genuinely believe in the effort and be willing to expend significant political capital on it. Your team also needs to be 100% on board.
If you can't make this happen and you're not working on a business which does immense social good and needs your support as a matter of charity, you should quit and go somewhere more comfortable.