There may be delays before updates made on the host are visible within a container.

Heres an illustration of the improvements in a few tools and applications in common use among Docker for Mac users: go list is 2.5 faster; symfony is 2.7 faster, and rake is 3.5 faster, as illustrated by the following graphs.

Docker Releases Series Of Incremental

In the filesystem, isolation shows up as layering: the filesystem of a running container consists of a series of incremental layers, topped by a container-specific readwrite layer that keeps changes made within the container concealed from the outside world.

For data-in-motion, Docker offers a variety of ways to connect containers via the network.

For data-at-rest, Docker Volumes offer a flexible mechanism to share data between containers, and with the host.

For example, the following command runs the alpine image, exposing the host directory Usersyallopproject within the container as project.

Consequently, access to bind mounts carries little-to-no overhead compared to filesystem access in a regular process.

Containers running on top of the Linux system cannot directly access macOS filesystem or networking resources, and so Docker for Mac includes libraries that expose those resources in a way that the Docker engine can consume.

A Linux system call such as open or read that accesses bind-mounted files in a container must be.

However, some software, written under the usually-correct assumption that system calls are instantaneous, can perform tens of thousands of system calls for each user-facing operation.

Even a comparatively low overhead can become irksome when scaled up by four orders of magnitude.

Consequently, although syscall latency has been reduced several times since the initial release of Docker for Mac, and although a few opportunities for further reducing latency remain, optimizing latency alone will not completely address bind mount performance for all applications.

On macOS maintaining consistency is not free: changes must be synchronously propagated between container and host.

Again, event propagation is automatic and free on Linux, but Docker for Mac must perform additional work to ensure that events are propagated promptly and reliably.

Using rsync to copy files into a container provides fast access, but does not support consistency.

Mounting directories into containers using NFS works well for some use cases, but does not support event propagation.

Reverse-mounting container directories onto the host might provide good performance for some workloads, but would require a very different interface.

In particular, a system that was not consistent by default would behave in ways that were unpredictable and surprising, especially for casual users, for users used to the Linux implementation, and for software invoking docker on the host.

In particular, although the Linux implementation guarantees that the container and host have consistent views at all times, temporary inconsistency between container and host is sometimes acceptable.

Allowing temporary inconsistency makes it possible to cache filesystem state, avoiding unnecessary communication between the container and macOS, and increasing performance.

Docker Releases Full Consistency Is

Full consistency is sometimes essential, and remains the default.

The container runtime and the host maintain an identical view of the mount at all times.

Docker For Mac Releases