Multiple applications in multiple containers vs Multiple applications in single container

As a beginner in Docker or container, people always ask why I can't put all the application in a single container and deploy it to anywhere?
Well, technically you can but here are some considerations.

	Multiple Applications in Multiple Containers	Multiple Applications in a Single Container
Isolation	Each application runs in its own environment	All applications share the same environment
Scaling	Different parts of an application can be scaled independently	All applications must be scaled together
Upgrades	One part of an application can be upgraded without affecting the rest	Upgrading one application may require restarting all applications
Reuse	Easier to reuse prebuilt images	Not as straightforward to reuse prebuilt images
Simplicity	Need to manage networking between containers	No need to manage networking between containers
Tightly-Coupled Processes	Not a concern if applications are loosely coupled	Might be a requirement if applications are tightly coupled

Source:

• Why multi-container docker apps are built? - Stack Overflow.
• Multi container apps | Docker Docs.
• Containers: one single process, or multiple processes?.
• Best way to run multiple flask apps in a single docker container.
• Tutorial: Create a multi-container app with Docker Compose.