skopeo

Please be aware skopeo is still work in progress

skopeo is a command line utility which is able to inspect a repository on a Docker registry. By inspect I mean it fetches the repository's manifest and it is able to show you a docker inspect-like json output about a whole repository or a tag. This tool, in constrast to docker inspect, helps you gather useful information about a repository or a tag before pulling it (using disk space) - e.g. - which tags are available for the given repository? which labels the image has?

Examples:

# show repository's labels of rhel7:latest
$ skopeo registry.access.redhat.com/rhel7 | jq '.Config.Labels'
{
  "Architecture": "x86_64",
  "Authoritative_Registry": "registry.access.redhat.com",
  "BZComponent": "rhel-server-docker",
  "Build_Host": "rcm-img04.build.eng.bos.redhat.com",
  "Name": "rhel7/rhel",
  "Release": "38",
  "Vendor": "Red Hat, Inc.",
  "Version": "7.2"
}

# show repository's tags
$ skopeo docker.io/fedora | jq '.RepoTags'
[
  "20",
  "21",
  "22",
  "23",
  "heisenbug",
  "latest",
  "rawhide"
]

# show image's digest
$ skopeo docker.io/fedora:rawhide | jq '.Digest'
"sha256:905b4846938c8aef94f52f3e41a11398ae5b40f5855fb0e40ed9c157e721d7f8"

Private registries with authentication

When interacting with private registries, skopeo first looks for the Docker's cli config file (usually located at $HOME/.docker/config.json) to get the credentials needed to authenticate. When the file isn't available it falls back looking for --username and --password flags. The ultimate fallback, as Docker does, is to provide an empty authentication when interacting with those registries.

Examples:

# on my system
$ skopeo --help | grep docker-cfg
   --docker-cfg "/home/runcom/.docker"	Docker's cli config for auth

$ cat /home/runcom/.docker/config.json
{
	"auths": {
		"myregistrydomain.com:5000": {
			"auth": "dGVzdHVzZXI6dGVzdHBhc3N3b3Jk",
			"email": "stuf@ex.cm"
		}
	}
}

# we can see I'm already authenticated via docker login so everything will be fine
$ skopeo myregistrydomain.com:5000/busybox
{"Tag":"latest","Digest":"sha256:473bb2189d7b913ed7187a33d11e743fdc2f88931122a44d91a301b64419f092","RepoTags":["latest"],"Comment":"","Created":"2016-01-15T18:06:41.282540103Z","ContainerConfig":{"Hostname":"aded96b43f48","Domainname":"","User":"","AttachStdin":false,"AttachStdout":false,"AttachStderr":false,"Tty":false,"OpenStdin":false,"StdinOnce":false,"Env":null,"Cmd":["/bin/sh","-c","#(nop) CMD [\"sh\"]"],"Image":"9e77fef7a1c9f989988c06620dabc4020c607885b959a2cbd7c2283c91da3e33","Volumes":null,"WorkingDir":"","Entrypoint":null,"OnBuild":null,"Labels":null},"DockerVersion":"1.8.3","Author":"","Config":{"Hostname":"aded96b43f48","Domainname":"","User":"","AttachStdin":false,"AttachStdout":false,"AttachStderr":false,"Tty":false,"OpenStdin":false,"StdinOnce":false,"Env":null,"Cmd":["sh"],"Image":"9e77fef7a1c9f989988c06620dabc4020c607885b959a2cbd7c2283c91da3e33","Volumes":null,"WorkingDir":"","Entrypoint":null,"OnBuild":null,"Labels":null},"Architecture":"amd64","Os":"linux"}

# let's try now to fake a non existent Docker's config file
$ skopeo --docker-cfg="" myregistrydomain.com:5000/busybox
INFO[0000] Docker cli config file not found: stat : no such file or directory, falling back to --username and --password
FATA[0000] unable to ping registry endpoint http://myregistrydomain.com:5000/v0/
v2 ping attempt failed with error: Get http://myregistrydomain.com:5000/v2/: malformed HTTP response "\x15\x03\x01\x00\x02\x02"
 v1 ping attempt failed with error: Get http://myregistrydomain.com:5000/v1/_ping: malformed HTTP response "\x15\x03\x01\x00\x02\x02"

# we can see the cli config isn't found so it looks for --username and --password
# but because I didn't provide them I can't auth to the registry and I receive the above error
INFO[0000] Docker cli config file not found: stat : no such file or directory, falling back to --username and --password

# passing --username and --password - we can see that everything goes fine despite an info showing
# cli config can't be found
$ skopeo --docker-cfg="" --username=testuser --password=testpassword myregistrydomain.com:5000/busybox
INFO[0000] Docker cli config file not found: stat : no such file or directory, falling back to --username and --password
{"Tag":"latest","Digest":"sha256:473bb2189d7b913ed7187a33d11e743fdc2f88931122a44d91a301b64419f092","RepoTags":["latest"],"Comment":"","Created":"2016-01-15T18:06:41.282540103Z","ContainerConfig":{"Hostname":"aded96b43f48","Domainname":"","User":"","AttachStdin":false,"AttachStdout":false,"AttachStderr":false,"Tty":false,"OpenStdin":false,"StdinOnce":false,"Env":null,"Cmd":["/bin/sh","-c","#(nop) CMD [\"sh\"]"],"Image":"9e77fef7a1c9f989988c06620dabc4020c607885b959a2cbd7c2283c91da3e33","Volumes":null,"WorkingDir":"","Entrypoint":null,"OnBuild":null,"Labels":null},"DockerVersion":"1.8.3","Author":"","Config":{"Hostname":"aded96b43f48","Domainname":"","User":"","AttachStdin":false,"AttachStdout":false,"AttachStderr":false,"Tty":false,"OpenStdin":false,"StdinOnce":false,"Env":null,"Cmd":["sh"],"Image":"9e77fef7a1c9f989988c06620dabc4020c607885b959a2cbd7c2283c91da3e33","Volumes":null,"WorkingDir":"","Entrypoint":null,"OnBuild":null,"Labels":null},"Architecture":"amd64","Os":"linux"}

If your cli config is found but it doesn't contain the necessary credentials for the queried registry you'll get an error. You can fix this by either logging in (via docker login) or providing --username and --password. Building

$ git clone https://github.com/runcom/skopeo
$ make

Installing

$ sudo make install

TODO

• show repo tags via flag or when reference isn't tagged or digested
• add tests (integration with deployed registries in container - Docker-like)

NOT TODO

• provide a format flag - just use the awesome jq

License

MIT