When comparing Symfony 4 vs Lumen, the Slant community recommends Lumen for most people. In the question“What are the best PHP frameworks for building a RESTful API?” Lumen is ranked 2nd while Symfony 4 is ranked 4th. The most important reason people chose Lumen is:
Since it's basically just a minimal version of Laravel, it can be upgraded to a full Laravel app if the need arises. No need for code changes, just import the code to a new Laravel install.
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Pros
Pro Easily upgradable to Laravel
Since it's basically just a minimal version of Laravel, it can be upgraded to a full Laravel app if the need arises. No need for code changes, just import the code to a new Laravel install.
Pro Feature rich
Pro Highest performing PHP micro-Framework
Lumen is benchmarked at 100/rps (Requests Per Second) faster than Slim v3, which used to be considered the fastest and most performant micro-Framework to date with the ability to handle 1800/rps. (1900/rps vs 1800/rps respectively).
Pro Easy to use
Cons
Con Built for smaller tasks like APIs
Con It's based off Laravel and inherits its shortcomings
Lumen inherits many shortcomings of Laravel, such as static proxy classes.
Con Made to work alongside Laravel
Lumen as a framework is at it's full potential when used alongside it's older brother. Lumen was created to be used for microservices alongside Laravel, which is used for more user-facing applications. If a project is already using another framework other than Laravel, it would be better to use another microframework for microservices instead of Lumen.