Using the shell form instead of the exec form for CMD and ENTRYPOINT instructions in Dockerfiles can lead to several issues. When you use the shell
form, the executable runs as a child process to a shell, which does not pass OS signals. This can cause problems when trying to gracefully stop
containers because the main process will not receive the signal intended to terminate it. Moreover, the exec form provides more control and
predictability over the execution of the command. It does not invoke a command shell, which means it does not have the potential side effects of shell
processing.
Exceptions
The exec form does not allow shell features such as variable expansion, piping (|) and command chaining (&&,
||, ;). In case you need to use these features, there are a few alternatives: * Creation of a wrapper script * Explicitly
specify the shell to use with the SHELL instruction before CMD or ENTRYPOINT
This rule will not raise an issue if the SHELL instruction is used before the CMD or ENTRYPOINT instruction,
as we consider this a conscious decision.
