Docker containers are not the one and only solution for every single workload. There are services that do not fit into this concept, too. The major services that do not fit are as follows:

• Containers are not as fast as bare-metal installations. Even though a Docker container has less overhead than VMs, it does not have zero overhead. If your solution needs bare-metal speed, especially from the app point of view, you will have no choice but to run it directly from a bare-metal server, without using containers or virtual machines.
• Containers provide cross-platform compatibility, which means that a container designed to run in a Docker container may run in a Windows container, and vice versa. If you design your container to be flexible with the underlying operating system, you may lose features that often lead software architects to not provide this OS compatibility within containers at all.
• Containers are not designed to run applications with graphical interfaces. Although some tricks may provide this feature, the result is more than clunky. Docker is not a good solution for applications that require rich interfaces.
• Using Docker may provide a way to improve security, as its concept involves isolating applications from the host system and breaking an application into small microservices. This means that if one microservice is compromised, the others are not necessarily compromised, too. On the other hand, containerization brings additional requirements for security as it is a highly scalable environment, and this means that you will need to monitor the complete solution somehow.