如何搭建及使用docker registry

registry是什么？
registry是Docker的镜像存储服务，docker hub上的registry镜像见Registry官方镜像，更多详细信息请参见源码。
搭建registry
在服务器上执行如下命令安装docker，这里选择腾讯云（Ubuntu Server 14.04.1 LTS 64位）镜像来创建服务器
curl -fsSL https://get.docker.com/ | sh

安装docker-compose Docker Compose是一个定义及运行多个Docker容器的工具。使用Docker Compose只需要在一个配置文件中定义多个Docker容器，然后使用一条命令将多个容器启动，Docker Compose会通过解析容器间的依赖关系，按先后顺序启动所定义的容器。详见Docker Compose
curl -L https://github.com/docker/compose/releases/download/1.8.0/docker-compose-$(uname -s)-$(uname -m) > /usr/local/bin/docker-compose
chmod a+x /usr/local/bin/docker-compose

启动registry服务，此例中包含nginx和registry两个容器，涉及的包及配置文件请参见附件，解压后，直接执行如下命令即可创建服务。
docker-compose up -d

停止服务
docker-compose stop

重启服务
docker-compose restart

下线服务
docker-compose down

上传镜像
因为上面搭建的registry服务是http的，所以docker启动参数需要配置--insecure-registry localhost选项，修改/etc/default/docker文件
DOCKER_OPTS="--insecure-registry localhost"

重启docker
service docker restart

拉取上传镜像 docker pull;docker tag;docker push(tag默认为latest)
docker pull hello-world
docker tag hello-world localhost/library/hello-world
docker push localhost/library/hello-world

下载镜像
docker pull localhost/library/hello-world

删除镜像
docker rmi localhost/library/hello-world

获取镜像仓库列表
# curl http://localhost/v2/_catalog
{"repositories":["library/hello-world"]}

未上传镜像前的输出如下：
# curl http://localhost/v2/_catalog
{"repositories":[]}

获取镜像tag列表
# curl -X GET http://localhost/v2/library/hello-world/tags/list
{"name":"library/hello-world","tags":["latest"]}

获取镜像manifests信息
# curl -H "Accept: application/vnd.docker.distribution.manifest.v2+json" -X GET http://localhost/v2/library/hello-world/manifests/latest
{
"schemaVersion": 2,
"mediaType": "application/vnd.docker.distribution.manifest.v2+json",
"config": {
"mediaType": "application/vnd.docker.container.image.v1+json",
"size": 1473,
"digest": "sha256:c54a2cc56cbb2f04003c1cd4507e118af7c0d340fe7e2720f70976c4b75237dc"
},
"layers": [
{
"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
"size": 974,
"digest": "sha256:c04b14da8d1441880ed3fe6106fb2cc6fa1c9661846ac0266b8a5ec8edf37b7c"
}
]
}

其中c54a2cc56cbb2f04003c1cd4507e118af7c0d340fe7e2720f70976c4b75237dc即为执行docker images时看到的IMAGE ID。 layers表示了镜像的层次关系，可以通过layers中的digest来拉取blob，见下面获取镜像blob
获取镜像blob
在上面获取hello-world:latest镜像的manifests信息中可以看到其只有一个layer，以此为例来看如何获取镜像blob。从拉取的结果可以看到获取的blob与文件sha256是一致的。执行docker pull实际上就是首先获取到镜像的manifests信息后，再拉取blob的。
# curl -s -X GET http://localhost/v2/library/hello-world/blobs/sha256:c04b14da8d1441880ed3fe6106fb2cc6fa1c9661846ac0266b8a5ec8edf37b7c -o hello-world.blob
# ls -l hello-world.blob
-rw-r--r-- 1 root root 974 Nov 23 09:56 hello-world.blob
# sha256sum hello-world.blob
c04b14da8d1441880ed3fe6106fb2cc6fa1c9661846ac0266b8a5ec8edf37b7c hello-world.blob

##删除镜像(soft delete)
首先通过curl -i 参数获取到镜像的Docker-Content-Digest，registry 2.3及以后的版本必须在header中指定Accept: application/vnd.docker.distribution.manifest.v2+json，否则默认返回的是schema1的digest，其与schema2的digest不同，使用不指定上述头信息返回的digest删除时会返回404。
# curl -i -H "Accept: application/vnd.docker.distribution.manifest.v2+json" -X GET http://localhost/v2/library/hello-world/manifests/latest

HTTP/1.1 200 OK
Server: nginx/1.11.5
Date: Wed, 23 Nov 2016 02:17:51 GMT
Content-Type: application/vnd.docker.distribution.manifest.v2+json
Content-Length: 524
Connection: keep-alive
Docker-Content-Digest: sha256:a18ed77532f6d6781500db650194e0f9396ba5f05f8b50d4046b294ae5f83aa4
Docker-Distribution-Api-Version: registry/2.0
Etag: "sha256:a18ed77532f6d6781500db650194e0f9396ba5f05f8b50d4046b294ae5f83aa4"

{
"schemaVersion": 2,
"mediaType": "application/vnd.docker.distribution.manifest.v2+json",
"config": {
"mediaType": "application/vnd.docker.container.image.v1+json",
"size": 1473,
"digest": "sha256:c54a2cc56cbb2f04003c1cd4507e118af7c0d340fe7e2720f70976c4b75237dc"
},
"layers": [
{
"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
"size": 974,
"digest": "sha256:c04b14da8d1441880ed3fe6106fb2cc6fa1c9661846ac0266b8a5ec8edf37b7c"
}
]
}

根据上一步返回的Docker-Content-Digest删除，返回202表示删除成功
# curl -k -v -s -X DELETE http://localhost/v2/library/hello-world/manifests/sha256:a18ed77532f6d6781500db650194e0f9396ba5f05f8b50d4046b294ae5f83aa4

* Hostname was NOT found in DNS cache
* Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 80 (#0)
> DELETE /v2/library/hello-world/manifests/sha256:a18ed77532f6d6781500db650194e0f9396ba5f05f8b50d4046b294ae5f83aa4 HTTP/1.1
> User-Agent: curl/7.35.0
> Host: localhost
> Accept: */*
>
< **HTTP/1.1 202 Accepted**
* Server nginx/1.11.5 is not blacklisted
< Server: nginx/1.11.5
< Date: Wed, 23 Nov 2016 02:29:59 GMT
< Content-Type: text/plain; charset=utf-8
< Content-Length: 0
< Connection: keep-alive
< Docker-Distribution-Api-Version: registry/2.0
<
* Connection #0 to host localhost left intact

确认结果
# curl -X GET http://localhost/v2/library/hello-world/tags/list
{"name":"library/hello-world","tags":null}

删除镜像(hard delete)
在上一步中，只是删除了镜像的manifests信息，解引用的blob还在占用磁盘空间，执行如下命令可以查看可以删除的blob
docker exec -it myregistry_registry_1 /bin/registry garbage-collect --dry-run /etc/registry/config.yml

要删除blob，释放磁盘空间，需要执行下面的命令。需要特别注意的是在执行下面的命令时registry必须是只读模式（只读模式可在registry配置文件中设置），否则可能会导致数据不一致。
docker exec -it myregistry_registry_1 /bin/registry garbage-collect /etc/registry/