Docker-Extra

The docker-extra branch is based on moby project, it modifies the code to allow docker pull from a extra image storage when downloading images.

Download the package from release page.

Introduction

Pulling a big image from remote registry can be very slow, while a container only needs a little data to boot up accroding to some expriments, so it's effcient that docker have the access to some extra image layer storage, e.g. NFS layer storage, which stores uncompressed image data, then a container can be started just upon the layer storage and the data is requested through wire in a so called "Lazy" way.

docker-extra project provides a way to allow docker work with those extra (may be shared) storage, which speed up the creation of container.

Features

We add some other options to dockerd's config file (/etc/docker/daemon.json):

{
    "extra-storage":{
        "path":"path-to-the-extra-storage-dir-on-host[default:/var/lib/docker/extra]",
        "device":"path-to-the-device-to-be-mount-on-path",
        "type":"mount-type"
    }
}

If the extra storage is just a dir on host, then the path option is enough. If the extra storage is intalled as a device and should be mount on the dir path, users should specify the path of the device (e.g. /dev/sdb0) and also the type of the file system (e.g. ext4)

Once the extra-storage is ready, you can pull the image from extra storage with a "-extra" or "extra" flag at the end of the image tag. For example, pulling centos7 from extra storage:

docker pull centos:7-extra

or pulling the latest version of ubuntu from extra storage:

docker pull ubuntu:extra

Extra Storage Requirment

File structure of extra storage dir should be like the one below

It's easy to create a required extra storage structure, you can just copy the image and overlay2 from /var/lib/docker/.

Build

Merge all the code changes in diff or use fils in full to replace the corresponding files in projcet, then follow the steps here to build this project.

Build rpm packages

1. clone docker-ce-packaging project

git clone https://github.com/docker/docker-ce-packaging.git

2. enter subdir rpm of docker-ce-packaging
3. follow the steps here to create rpm packages for docker.