The cause: the file system calls
Your source code is mounted from your osx host’s filesytem to your Docker (Linux) filesystem. For them to communicate together, every call to your mounted volume uses the osxfs shared file system solution. As described in this post, a call will undergo the following process, back and forth:
turned into a FUSE message in the Linux VFS
proxied over a virtio socket by transfused
forwarded onto a UNIX domain socket by HyperKit
deserialized, dispatched and executed as a macOS system call by osxfs
Now, some languages, such as php or python, expect system calls to be instantaneous. Thus, they will retry until they get an answer. These thousands of parasite calls will result in an overhead causing latency. Although Docker has made some effort to reduce this problem, it is still insufficient, but cool opensource projects such as docker-sync solve the problem.
A workaround with docker-sync
Docker-sync is a tool that allows a two way and asynchronous synchronization. It will drastically improve the performances and make the comparable to running docker on a linux host. If you want to know more about the process, go check the documentation here.
Here is a guide to quickly solve your issue:
Install docker sync with rubby on any OS with the command: `gem install docker-sync`.
Configure your project to use docker-sync
Let’s say you have a
Dockerfile and a
docker-compose.yaml. A minimal
docker-compose.yaml would look something like that
docker-sync.yaml file and past in this configuration. More options are available, you can check them here:
Create the volume that will keep the
src defined above by running
docker volume create api-sync
Update your docker compose to refer to this volume
Run the command
docker-sync start --config=<path-to-docker-sync.yaml>
You should define sync for every volume you mount from your host. For instance, if your db stores persistent data...
Note that if you change your
docker-sync clean and
docker-sync start to refresh your volumes. Run
docker-sync stop to stop docker-sync
You are now ready to use your app
docker-compose up -d.