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NAME
containers-registries.conf - Syntax of System Registry Configuration File
DESCRIPTION
The CONTAINERS-REGISTRIES configuration file is a system-wide configuration file for container image
registries. The file format is TOML.
Container engines will use the $HOME/.config/containers/registries.conf if it exists, otherwise they will
use /etc/containers/registries.conf
GLOBAL SETTINGS
unqualified-search-registries
An array of host[:port] registries to try when pulling an unqualified image, in order.
credential-helpers
An array of default credential helpers used as external credential stores. Note that "containers-
auth.json" is a reserved value to use auth files as specified in containers-auth.json(5). The
credential helpers are set to ["containers-auth.json"] if none are specified.
additional-layer-store-auth-helper
A string containing the helper binary name. This enables passing registry credentials to an
Additional Layer Store every time an image is read using the docker:// transport so that it can
access private registries. See the 'Enabling Additional Layer Store to access to private
registries' section below for more details.
NAMESPACED [[registry]] SETTINGS
The bulk of the configuration is represented as an array of [[registry]] TOML tables; the settings may
therefore differ among different registries as well as among different namespaces/repositories within a
registry.
Choosing a [[registry]] TOML table
Given an image name, a single [[registry]] TOML table is chosen based on its prefix field.
prefix: A prefix of the user-specified image name, i.e. using one of the following formats:
- host[:port]
- host[:port]/namespace[/_namespace_…]
- host[:port]/namespace[/_namespace_…]/repo
- host[:port]/namespace[/_namespace_…]/repo(:_tag|@digest)
- [*.]host
The user-specified image name must start with the specified prefix (and continue with the appropriate
separator) for a particular [[registry]] TOML table to be considered; (only) the TOML table with the
longest match is used. It can also include wildcarded subdomains in the format *.example.com. The
wildcard should only be present at the beginning as shown in the formats above. Other cases will not
work. For example, *.example.com is valid but example.*.com, *.example.com/foo and
*.example.com:5000/foo/bar:baz are not. Note that * matches an arbitrary number of subdomains.
*.example.com will hence match bar.example.com, foo.bar.example.com and so on.
As a special case, the prefix field can be missing; if so, it defaults to the value of the location field
(described below).
Per-namespace settings
insecure
true or false. By default, container runtimes require TLS when retrieving images from a registry.
If insecure is set to true, unencrypted HTTP as well as TLS connections with untrusted
certificates are allowed.
blocked
true or false. If true, pulling images with matching names is forbidden.
Remapping and mirroring registries
The user-specified image reference is, primarily, a "logical" image name, always used for naming the
image. By default, the image reference also directly specifies the registry and repository to use, but
the following options can be used to redirect the underlying accesses to different registry servers or
locations (e.g. to support configurations with no access to the internet without having to change
Dockerfiles, or to add redundancy).
location
Accepts the same format as the prefix field, and specifies the physical location of the prefix-
rooted namespace.
By default, this is equal to prefix (in which case prefix can be omitted and the [[registry]] TOML table
can only specify location).
Example: Given
prefix = "example.com/foo"
location = "internal-registry-for-example.com/bar"
requests for the image example.com/foo/myimage:latest will actually work with the internal-registry-for-
example.com/bar/myimage:latest image.
With a prefix containing a wildcard in the format: "*.example.com" for subdomain matching, the location
can be empty. In such a case, prefix matching will occur, but no reference rewrite will occur. The
original requested image string will be used as-is. But other settings like insecure / blocked / mirrors
will be applied to matching images.
Example: Given
prefix = "*.example.com"
requests for the image blah.example.com/foo/myimage:latest will be used as-is. But other settings like
insecure/blocked/mirrors will be applied to matching images
mirror An array of TOML tables specifying (possibly-partial) mirrors for the prefix-rooted namespace
(i.e., the current [[registry]] TOML table).
The mirrors are attempted in the specified order; the first one that can be contacted and contains the
image will be used (and if none of the mirrors contains the image, the primary location specified by the
registry.location field, or using the unmodified user-specified reference, is tried last).
Each TOML table in the mirror array can contain the following fields: - location： same semantics as
specified in the [[registry]] TOML table - insecure： same semantics as specified in the [[registry]]
TOML table - pull-from-mirror: all, digest-only or tag-only. If "digest-only"， mirrors will only be
used for digest pulls. Pulling images by tag can potentially yield different images, depending on which
endpoint we pull from. Restricting mirrors to pulls by digest avoids that issue. If "tag-only", mirrors
will only be used for tag pulls. For a more up-to-date and expensive mirror that it is less likely to be
out of sync if tags move, it should not be unnecessarily used for digest references. Default is "all"
(or left empty), mirrors will be used for both digest pulls and tag pulls unless the mirror-by-digest-
only is set for the primary registry. Note that this per-mirror setting is allowed only when mirror-by-
digest-only is not configured for the primary registry.
mirror-by-digest-only
true or false. If true, mirrors will only be used during pulling if the image reference includes
a digest. Note that if all mirrors are configured to be digest-only, images referenced by a tag
will only use the primary registry. If all mirrors are configured to be tag-only, images
referenced by a digest will only use the primary registry.
Referencing an image by digest ensures that the same is always used (whereas referencing an image by a
tag may cause different registries to return different images if the tag mapping is out of sync).
Note: Redirection and mirrors are currently processed only when reading a single image, not when pushing
to a registry nor when doing any other kind of lookup/search on a on a registry. This may change in the
future.
Short-Name Aliasing
The use of unqualified-search registries entails an ambiguity as it is unclear from which registry a
given image, referenced by a short name, may be pulled from.
As mentioned in the note at the end of this man page, using short names is subject to the risk of hitting
squatted registry namespaces. If the unqualified-search registries are set to ["registry1.com",
"registry2.com"] an attacker may take over a namespace of registry1.com such that an image may be pulled
from registry1.com instead of the intended source registry2.com.
While it is highly recommended to always use fully-qualified image references, existing deployments using
short names may not be easily changed. To circumvent the aforementioned ambiguity, so called short-name
aliases can be configured that point to a fully-qualified image reference.
Short-name aliases can be configured in the [aliases] table in the form of "name"="value" with the left-
hand name being the short name (e.g., "image") and the right-hand value being the fully-qualified image
reference (e.g., "registry.com/namespace/image"). Note that neither "name" nor "value" can include a tag
or digest. Moreover, "name" must be a short name and hence cannot include a registry domain or refer to
localhost.
When pulling a short name, the configured aliases table will be used for resolving the short name. If a
matching alias is found, it will be used without further consulting the unqualified-search registries
list. If no matching alias is found, the behavior can be controlled via the short-name-mode option as
described below.
Note that tags and digests are stripped off a user-specified short name for alias resolution. Hence,
"image", "image:tag" and "image@digest" all resolve to the same alias (i.e., "image"). Stripped off tags
and digests are later appended to the resolved alias.
Further note that drop-in configuration files (see containers-registries.conf.d(5)) can override aliases
in the specific loading order of the files. If the "value" of an alias is empty (i.e., ""), the alias
will be erased. However, a given "name" may only be specified once in a single config file.
Short-Name Aliasing: Modes
The short-name-mode option supports three modes to control the behaviour of short-name resolution.
• enforcing: If only one unqualified-search registry is set, use it as there is no ambiguity. If
there is more than one registry and the user program is running in a terminal (i.e., stdout &
stdin are a TTY), prompt the user to select one of the specified search registries. If the
program is not running in a terminal, the ambiguity cannot be resolved which will lead to an
error.
• permissive: Behaves as enforcing but does not lead to an error if the program is not running in
a terminal. Instead, fallback to using all unqualified-search registries.
• disabled: Use all unqualified-search registries without prompting.
If short-name-mode is not specified at all or left empty, default to the permissive mode. If the user-
specified short name was not aliased already, the enforcing and permissive mode if prompted, will record
a new alias after a successful pull. Note that the recorded alias will be written to
/var/cache/containers/short-name-aliases.conf for root to have a clear separation between possibly human-
edited registries.conf files and the machine-generated short-name-aliases-conf. Note that $HOME/.cache
is used for rootless users. If an alias is specified in a registries.conf file and also the machine-
generated short-name-aliases.conf, the short-name-aliases.conf file has precedence.
Normalization of docker.io references
The Docker Hub docker.io is handled in a special way: every push and pull operation gets internally
normalized with /library if no other specific namespace is defined (for example on
docker.io/namespace/image).
(Note that the above-described normalization happens to match the behavior of Docker.)
This means that a pull of docker.io/alpine will be internally translated to docker.io/library/alpine. A
pull of docker.io/user/alpine will not be rewritten because this is already the correct remote path.
Therefore, to remap or mirror the docker.io images in the (implied) /library namespace (or that whole
namespace), the prefix and location fields in this configuration file must explicitly include that
/library namespace. For example prefix = "docker.io/library/alpine" and not prefix = "docker.io/alpine".
The latter would match the docker.io/alpine/* repositories but not the docker.io/[library/]alpine image).
EXAMPLE
unqualified-search-registries = ["example.com"]
[[registry]]
prefix = "example.com/foo"
insecure = false
blocked = false
location = "internal-registry-for-example.com/bar"
[[registry.mirror]]
location = "example-mirror-0.local/mirror-for-foo"
[[registry.mirror]]
location = "example-mirror-1.local/mirrors/foo"
insecure = true
[[registry]]
location = "registry.com"
[[registry.mirror]]
location = "mirror.registry.com"
Given the above, a pull of example.com/foo/image:latest will try:
1. example-mirror-0.local/mirror-for-foo/image:latest
2. example-mirror-1.local/mirrors/foo/image:latest
3. internal-registry-for-example.com/bar/image:latest
in order, and use the first one that exists.
Note that a mirror is associated only with the current [[registry]] TOML table. If using the example
above, pulling the image registry.com/image:latest will hence only reach out to mirror.registry.com, and
the mirrors associated with example.com/foo will not be considered.
Enabling Additional Layer Store to access to private registries
The additional-layer-store-auth-helper option enables passing registry credentials to an Additional Layer
Store so that it can access private registries.
When accessing a private registry via an Additional Layer Store, a helper binary needs to be provided.
This helper binary is registered via the additional-layer-store-auth-helper option. Every time an image
is read using the docker:// transport, the specified helper binary is executed and receives registry
credentials from stdin in the following format.
{
"$image_reference": {
"username": "$username",
"password": "$password",
"identityToken": "$identityToken"
}
}
The format of $image_reference is $repo{:$tag|@$digest}.
Additional Layer Stores can use this helper binary to access the private registry.
VERSION 1 FORMAT - DEPRECATED
VERSION 1 format is still supported but it does not support using registry mirrors, longest-prefix
matches, or location rewriting.
The TOML format is used to build a simple list of registries under three categories: registries.search,
registries.insecure, and registries.block. You can list multiple registries using a comma separated
list.
Search registries are used when the caller of a container runtime does not fully specify the container
image that they want to execute. These registries are prepended onto the front of the specified
container image until the named image is found at a registry.
Note that insecure registries can be used for any registry, not just the registries listed under search.
The registries.insecure and registries.block lists have the same meaning as the insecure and blocked
fields in the current version.
EXAMPLE
The following example configuration defines two searchable registries, one insecure registry, and two
blocked registries.
[registries.search]
registries = ['registry1.com', 'registry2.com']
[registries.insecure]
registries = ['registry3.com']
[registries.block]
registries = ['registry.untrusted.com', 'registry.unsafe.com']
NOTE: RISK OF USING UNQUALIFIED IMAGE NAMES
We recommend always using fully qualified image names including the registry server (full dns name),
namespace, image name, and tag (e.g., registry.redhat.io/ubi8/ubi:latest). When using short names, there
is always an inherent risk that the image being pulled could be spoofed. For example, a user wants to
pull an image named foobar from a registry and expects it to come from myregistry.com. If myregistry.com
is not first in the search list, an attacker could place a different foobar image at a registry earlier
in the search list. The user would accidentally pull and run the attacker's image and code rather than
the intended content. We recommend only adding registries which are completely trusted, i.e. registries
which don't allow unknown or anonymous users to create accounts with arbitrary names. This will prevent
an image from being spoofed, squatted or otherwise made insecure. If it is necessary to use one of these
registries, it should be added at the end of the list.
It is recommended to use fully-qualified images for pulling as the destination registry is unambiguous.
Pulling by digest (i.e., quay.io/repository/name@digest) further eliminates the ambiguity of tags.
SEE ALSO
containers-auth.json(5) containers-certs.d(5)
HISTORY
Dec 2019, Warning added for unqualified image names by Tom Sweeney tsweeney@redhat.com
⟨mailto:tsweeney@redhat.com⟩
Mar 2019, Added additional configuration format by Sascha Grunert sgrunert@suse.com
⟨mailto:sgrunert@suse.com⟩
Aug 2018, Renamed to containers-registries.conf(5) by Valentin Rothberg vrothberg@suse.com
⟨mailto:vrothberg@suse.com⟩
Jun 2018, Updated by Tom Sweeney tsweeney@redhat.com ⟨mailto:tsweeney@redhat.com⟩
Aug 2017, Originally compiled by Brent Baude bbaude@redhat.com ⟨mailto:bbaude@redhat.com⟩
registry System-wide CONTAINERS-REGISTRIES.CONF(5)