OCI Registry As Storage

oras can push/pull any files to/from any registry with OCI image support.

Registries with known support:

• Distribution (open source, version 2.7+)
• Azure Container Registry

For more background on this topic, please see this post.

Getting Started

First, you must have access to a registry with OCI image support (see list above).

The simplest way to get started is to run the official Docker registry image locally:

docker run -it --rm -p 5000:5000 registry:2.7.0

This will start a Distribution server at localhost:5000 (with wide-open access and no persistence).

Next, install the oras CLI (see platform-specific installation instructions below).

Push a sample file to the registry:

cd /tmp && echo "hello world" > hi.txt
oras push localhost:5000/hello:latest hi.txt

Pull the file from the registry:

cd /tmp && rm -f hi.txt
oras pull localhost:5000/hello:latest
cat hi.txt  # should print "hello world"

Please see the Go Module section below for how this can be imported and used inside a Go project.

CLI

oras is a CLI that allows you to push and pull files from any registry with OCI image support.

Installation

Install oras using GoFish:

gofish install oras
==> Installing oras...
🐠  oras 0.3.1: installed in 65.131245ms

or install manually from the latest release artifacts:

# Linux
curl -LO https://github.com/shizhMSFT/oras/releases/download/v0.3.1/oras_0.3.1_linux_amd64.tar.gz

# macOS
curl -LO https://github.com/shizhMSFT/oras/releases/download/v0.3.1/oras_0.3.1_darwin_amd64.tar.gz

# unpack, install, dispose
mkdir -p oras/
tar -zxf oras_0.3.1_*.tar.gz -C oras/
mv oras/bin/oras /usr/local/bin/
rm -rf oras_0.3.1_*.tar.gz oras/

Then, to run:

oras help

Docker Image

A public Docker image containing the CLI is available on Docker Hub:

docker run -it --rm -v $(pwd):/workspace ocistorage/oras:v0.3.1 help

Note: the default WORKDIR in the image is /workspace.

Login Credentials

oras uses the local Docker credentials by default. Please run docker login in advance for any private registries.

oras also accepts explicit credentials via options, for example,

oras pull -u username -p password myregistry.io/myimage:latest

Usage

Pushing files to remote registry

oras push localhost:5000/hello:latest hi.txt

The default media type for all files is application/vnd.oci.image.layer.v1.tar.

The push a custom media type, use the format filename[:type]:

oras push localhost:5000/hello:latest hi.txt:application/vnd.me.hi

To push multiple files with different media types:

oras push localhost:5000/hello:latest hi.txt:application/vnd.me.hi bye.txt:application/vnd.me.bye

Pulling files from remote registry

oras pull localhost:5000/hello:latest

By default, only blobs with media type application/vnd.oci.image.layer.v1.tar will be downloaded.

To specify which media types to download, use the --media-type/-t flag:

oras pull localhost:5000/hello:latest -t application/vnd.me.hi

Or to allow all media types, use the --allow-all/-a flag:

oras pull localhost:5000/hello:latest -a

Go Module

The package github.com/shizhMSFT/oras/pkg/oras can quickly be imported in other Go-based tools that wish to benefit from the ability to store arbitrary content in container registries.

Example:

Source

package main

import (
	"context"
	"fmt"

	"github.com/containerd/containerd/remotes/docker"
	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
	"github.com/shizhMSFT/oras/pkg/content"
	"github.com/shizhMSFT/oras/pkg/oras"
)

func check(e error) {
	if e != nil {
		panic(e)
	}
}

func main() {
	ref := "localhost:5000/oras:test"
	fileName := "hello.txt"
	fileContent := []byte("Hello World!\n")
	customMediaType := "my.custom.media.type"

	ctx := context.Background()
	resolver := docker.NewResolver(docker.ResolverOptions{})

	// Push file(s) w custom mediatype to registry
	memoryStore := content.NewMemoryStore()
	desc := memoryStore.Add(fileName, customMediaType, fileContent)
	pushContents := []ocispec.Descriptor{desc}
	fmt.Printf("Pushing %s to %s... ", fileName, ref)
	err := oras.Push(ctx, resolver, ref, memoryStore, pushContents)
	check(err)
	fmt.Println("success!")

	// Pull file(s) from registry and save to disk
	fmt.Printf("Pulling from %s and saving to %s... ", ref, fileName)
	fileStore := content.NewFileStore("")
	allowedMediaTypes := []string{customMediaType}
	_, err = oras.Pull(ctx, resolver, ref, fileStore, allowedMediaTypes...)
	check(err)
	fmt.Println("success!")
	fmt.Printf("Try running 'cat %s'\n", fileName)
}