demo VS sulu

In the contrary you need to start something to understand your exact needs. Build, test your image, rebuild until you get it right. If it's a Symfony app, here's an example: https://github.com/numberninecms/demo/blob/master/.github/workflows/staging.yml and the dockerfile https://github.com/numberninecms/demo/blob/master/docker/Dockerfile Basically you build your app on the host (php vendors, assets...) then move the files to the image. Alternatively you can build from within the dockerfile, not ideal in my opinion.

https://sulu.io/ or https://kunstmaancms.be/ if you want to stay with symfony. Both solid options

I want to try Sulu first because it is Symfony-based.

Another usecase are Framework based CMS System. Beside Drupal, Typo3 using example Symfony components, still are not Full Stack Symfony and don't use Symfony based folder structure and are so very different then using Symfony Full Stack based CMS. In this area other CMS like Sulu, Bolt, .. are placed which do not hide Symfony Full Stack and are more for the web applications which are not typical just a Website but has application based component in it which can be build with the Symfony components and ecosystem. This CMS are also mostly more version control friendly as most configurations are inside Code and not inside Database and the CMS admin concentrate on Content Management and configure the System itself. Another CMS which is more and more migrating Full Stack Symfony is Contao CMS, which definitly should not be forgotten.

Try something on Symfony. For example https://github.com/sulu/sulu. It's a CMS, but I've noticed that it has some domain-driven design principles implemented.

While I was working on Sulu CMS and did invest a lot about prototypes around Hexagonal Architecture. I did miss something specific in the PHP-Fig interfaces, a Interface for Template engines.