Goal

Analyse the behavior of fsnotify with a docker mounted volume.

Process

This project contains a simple Go app that show the events caught by fsnotify. The docker-compose file contains different configuration of the Go app to check the combination of mounted volumes and watched target. The file modifications are done on both the container and the host.

I used:

• Vi/Golang as editor to generate a Write notification.
• Vim to generate the Rename notification.

Volume mounted	Listen on	File action	From Host	From Container	Comment
file	file	Write	OK	OK	Live reload on save.
file	file	Rename	KO	OK	First event receive then nothing. All local changes (in container) are detected
file	directory	Write	KO	OK	Edition works only from container to host
file	directory	Rename	KO	OK	Edition works only from container to host
file	both	Write	OK	OK
file	both	Rename	KO	OK	Have the first event then the link is broken
file	both + reload	Rename	KO	OK
directory	file	Write	OK	OK
directory	file	Rename	KO	KO	The link is broken in the two directions
directory	directory	Write	OK	OK
directory	directory	Rename	OK	OK
directory	both	Write	OK	OK
directory	both	Rename	OK	OK

Conclusion

The main issue occurred with the Rename event, the link between the host and the container file is broken and no more event are shared. The other issue occurred with the Write event only when we watch for directory event on a mounted file.

App Usage

The simple app using fsnotify has two options that are available via flags.

--target

The watcher target, could be one of the following elements :

• file watch the file (default value)
• dir watch the file parent directory
• both watch the file and its parent directory

--reload

If true, try to create a new watcher on the file when a rename event occurred. The default value is false.