Скачать или смотреть Docker Architecture|Copy-on-write|Union Filesystem

Hello Everyone

So in the last video, we started talking about Docker Architecture and will continue to do so in this video as well.
Let's pick up from where we left and talk about Union FS, so I told you that

UnionFS enables docker to efficiently manage the storage of image layers and it presents multiple filesystems as a single mount.

Here we are specifically going to talk about overlay2, which is the docker storage driver that implements unionFS

Overlay2 has few layers

The base layer - this is the root layer of an image and is read-only - this is similar to the root filesystem of Linux. This is what you download when you fetch an image from docker hub

Next, we have an

Overlay layer - This you can consider as a working directory for users. So when you run a container, this layer gives the union view of base and diff layer

Last we have a diff layer: So when you change or modify a file in the base layer, those automatically stored in this layer.

when you make a change to file that is present in the base layer, overlayfs will copy that file to diff layer and make the modifications. This is called copy on write.

UnionFs present a lot of benefits
1) efficient storage management - it is because of this you can run several containers from a single image without exhausting your disk space.

2) Isolation of changes to container filesystem - this lets you start and stop containers with each container preserving its content.