Docker ARG, .dockerignore, and Volumes Explained for Developers

Docker's ARG directive allows developers to define build-time variables inside a Dockerfile that can be overridden during the image build using the --build-arg flag, but cannot be modified at container runtime. A .dockerignore file lets developers exclude unnecessary files and directories from the build context, reducing build size and improving speed. By default, data written inside a container is stored in a temporary writable layer and is lost when the container is deleted. Docker volumes solve this by persisting data independently of the container lifecycle, with two main types: bind mounts, which map a specific host directory to a container directory, and named volumes, which are fully managed by Docker and stored in a dedicated location on the host. Both volume types allow multiple containers to share data, and the stored data remains intact even after the associated container is removed.