Docker Identifiers

Identifiers

A Docker Container can be identified in three ways: long form UUID (Universally Unique Identifier), a short form UUID and by Name. Identifiers help prevent naming conflicts and facilitate automation.

• UUID
• Universally Unique Identifier
• Assigned to a container on creation.
• UUIDs come in two forms:
• a 64 character long form, e.g.
• “f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778”
• an abbreviated 12 character short form, e.g.
• “f78375b1c487”
• automatically generated and applied by the Docker daemon
• Identifiers are commonly displayed in a truncated 12-character form
• Name
• A container name is generated and automatically assigned
• Generated name format: <adjective>_<notable names>
• On the left a list of strings, approximately 90 adjectives
• On the right a list of approximately 150 "notable" scientists and hackers
• Manually assign a container name using the --name option

The NAMES column lists the generated and manually assigned names. "testvol" is a manually assigned container name.

• Images can be further identified using: image:[tag] and image@[digest]
• Image:[tag]
• :tag allows you to add a version to an image, e.g. ubuntu:16.04, where ubuntu is the image, 16.04 is the tag (or version)
• Image:[@digest]
• A content addressable identifier, e.g.  sha256:58e1a1bb75db1b5a24a462dd5e2915277ea06438c3f105138f97eb53149673c4
• As long as the makeup of the image is the same, it's DIGEST value is a predictable and referenceable value, i.e. two images with the same DIGEST value can be assumed to be the same image
• docker images --digests to display the DIGEST value of an image
• An image can be pulled using the DIGEST value
• Images and containers may be identified in one of three ways:

Identifier Type	Example Value	Length
UUID long identifier	f78375b1c887e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778	64-character
UUID short identifier	f78375b1c887	12-character
Name	Pseudo-random generated names	Variable
Tag	String identifying a version of an image	Variable
Digest	Calculated SHA value of an image	64-character


References:

• https://docs.docker.com/engine/reference/commandline/pull/
• https://github.com/docker/docker/blob/master/pkg/namesgenerator/names-generator.go

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