Symfony version(s) affected: 4.1.4

Description

I run Symfony on a readonly filesystem and I can see this in my logs:

[warning] Failed to save key "%5BSymfony%5CBundle%5CFrameworkBundle%5CController%5CRedirectController%5D%5B1%5D" (array)
[warning] Failed to save key "%5BSymfony%5CBundle%5CFrameworkBundle%5CController%5CRedirectController%23urlRedirectAction%5D%5B1%5D" (array)

The urlRedirectAction is interesting, it seems like the routing might be caching a redirect response?

Am I doing something wrong here? I though the cache could be generated once (before deploying) and be readonly.

How to reproduce

I would say deploy Symfony (with its cache generated) on a readonly filesystem. I deployed Symfony 4 with Bref and its Symfony integration on AWS Lambda for example.

Possible Solution

Additional context