How does Docker isolate applications?

Docker isolates applications using namespaces in the Linux kernel, which is a fundamental aspect of how containerization works. Namespaces provide an abstraction that allows processes to have their own view of system resources, offering a level of isolation between different running applications. This means that each container created by Docker has its own isolated environment, where it can operate independently from other containers and the host system, effectively enabling multiple applications to run simultaneously on the same physical host without interfering with one another.

The use of namespaces means that each container has its own network stack, process ID space, and user ID, along with its own filesystem if using overlay file system technology. This ensures that the containers don’t share system resources in a way that could lead to conflicts, making them behave as if they are running on separate machines, while still being lightweight and efficient compared to traditional virtual machines.

While unique IP addresses and file system permissions play roles in networking and access control, respectively, these mechanisms rely on namespaces for their implementation. Virtual machines, on the other hand, provide a different type of isolation, as they rely on hypervisors and create completely separate operating system instances.