a9561eb1b190625c9adb5a9513e72c4dedafc1cb2d4c5236c9a6957ec7dfd5a9.
+ Each layer is given an ID upon its creation.
+ It is represented as a hexadecimal encoding of 256 bits, e.g., a9561eb1b190625c9adb5a9513e72c4dedafc1cb2d4c5236c9a6957ec7dfd5a9.
Image IDs should be sufficiently random so as to be globally unique.
- 32 bytes read from /dev/urandom is sufficient for all
- practical purposes. Alternatively, an image ID may be derived as a
- cryptographic hash of image contents as the result is considered
- indistinguishable from random. The choice is left up to implementors.
+ 32 bytes read from /dev/urandom is sufficient for all practical purposes.
+ Alternatively, an image ID may be derived as a cryptographic hash of image contents as the result is considered indistinguishable from random.
+ The choice is left up to implementors.
parent field which
- refers to the Image from which another directly descends. An image
- contains a separate JSON metadata file and set of changes relative to
- the filesystem of its parent image. Image Ancestor and
- Image Descendant are also common terms.
+ Most layer metadata structs contain a parent field which refers to the Image from which another directly descends.
+ An image contains a separate JSON metadata file and set of changes relative to the filesystem of its parent image.
+ Image Ancestor and Image Descendant are also common terms.
:) is
- often referred to as a tag as well, though it strictly refers to the
- full name of an image. Acceptable values for a tag suffix are
- implementation specific, but they SHOULD be limited to the set of
- alphanumeric characters [a-zA-z0-9], punctuation
- characters [._-], and MUST NOT contain a :
- character.
+ A tag serves to map a descriptive, user-given name to any single image ID.
+ An image name suffix (the name component after :) is often referred to as a tag as well, though it strictly refers to the full name of an image.
+ Acceptable values for a tag suffix are implementation specific, but they SHOULD be limited to the set of alphanumeric characters [a-zA-z0-9], punctuation characters [._-], and MUST NOT contain a : character.
:). For example, in an image tagged with the name
- my-app:3.1.4, my-app is the Repository
- component of the name. Acceptable values for repository name are
- implementation specific, but they SHOULD be limited to the set of
- alphanumeric characters [a-zA-z0-9], and punctuation
- characters [._-], however it MAY contain additional
- / and : characters for organizational
- purposes, with the last : character being interpreted
- dividing the repository component of the name from the tag suffix
- component.
+ A collection of tags grouped under a common prefix (the name component before :).
+ For example, in an image tagged with the name my-app:3.1.4, my-app is the Repository component of the name.
+ Acceptable values for repository name are implementation specific, but they SHOULD be limited to the set of alphanumeric characters [a-zA-z0-9], and punctuation characters [._-], however it MAY contain additional / and : characters for organizational purposes, with the last : character being interpreted dividing the repository component of the name from the tag suffix component.
string
string
string
string
@@ -198,15 +160,14 @@ Here is an example image JSON file:
architecture string
string
@@ -226,24 +187,20 @@ Here is an example image JSON file:
checksum string
integer
struct
null, in
- which case any execution parameters should be specified at creation of
- the container.
+ The execution parameters which should be used as a base when running a container using the image.
+ This field can be null, in which case any execution parameters should be specified at creation of the container.
string
The username or UID which the process in the container should - run as. This acts as a default value to use when the value is - not specified when creating a container.
++ The username or UID which the process in the container should run as. + This acts as a default value to use when the value is not specified when creating a container. +
All of the following are valid:
@@ -267,44 +225,38 @@ Here is an example image JSON file:user:gidIf group/gid is not specified, the
- default group and supplementary groups of the given
- user/uid in /etc/passwd
- from the container are applied.
+ If group/gid is not specified, the default group and supplementary groups of the given user/uid in /etc/passwd from the container are applied.
+
integer
integer
-1 to
- disable swap. This acts as a default value to use when the
- value is not specified when creating a container.
+ Total memory usage (memory + swap); set to -1 to disable swap.
+ This acts as a default value to use when the value is not specified when creating a container.
integer
struct
map[string]struct{} and is represented in JSON as
- an object mapping its keys to an empty object. Here is an
- example:
+ This JSON structure value is unusual because it is a direct JSON serialization of the Go type map[string]struct{} and is represented in JSON as an object mapping its keys to an empty object.
+ Here is an example:
{
"8080": {},
@@ -324,48 +276,39 @@ Here is an example image JSON file:
"port"
- with the default protocol being "tcp" if not
- specified.
+ with the default protocol being "tcp" if not specified.
- These values act as defaults and are merged with any specified
- when creating a container.
+ These values act as defaults and are merged with any specified when creating a container.
array of strings
VARNAME="var value".
- These values act as defaults and are merged with any specified
- when creating a container.
+ These values act as defaults and are merged with any specified when creating a container.
array of strings
array of strings
Entrypoint value is
- not specified, then the first entry of the Cmd
- array should be interpreted as the executable to run.
+ Default arguments to the entry point of the container.
+ These values act as defaults and are replaced with any specified when creating a container.
+ If an Entrypoint value is not specified, then the first entry of the Cmd array should be interpreted as the executable to run.
struct
map[string]struct{} and is represented in
- JSON as an object mapping its keys to an empty object. Here is
- an example:
+ A set of directories which should be created as data volumes in a container running this image.
+ This JSON structure value is unusual because it is a direct JSON serialization of the Go type map[string]struct{} and is represented in JSON as an object mapping its keys to an empty object.
+ Here is an example:
{
"/var/my-app-data/": {},
"/etc/some-config.d/": {},
@@ -375,28 +318,22 @@ Here is an example image JSON file:
WorkingDir string