<registry_server>/<user_name>/<image_name>:<tag>
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Managing Images
Overview
An image stream comprises any number of container images identified by tags. It presents a single virtual view of related images, similar to a Docker image repository.
By watching an image stream, builds and deployments can receive notifications when new images are added or modified and react by performing a build or deployment, respectively.
There are many ways you can interact with images and set up image streams, depending on where the images' registries are located, any authentication requirements around those registries, and how you want your builds and deployments to behave. The following sections cover a range of these topics.
Tagging Images
Before working with OpenShift Container Platform image streams and their tags, it helps to first understand image tags in the context of container images generally.
Container images can have names added to them that make it more intuitive to determine what they contain, called a tag. Using a tag to specify the version of what is contained in the image is a common use case. If you have an image named ruby, you could have a tag named 2.0 for 2.0 version of Ruby, and another named latest to indicate literally the latest built image in that repository overall.
When interacting directly with images using the docker CLI, the docker tag
command can add tags, which essentially adds an alias to an image that can
consist of several parts. Those parts can include:
The <user_name> part in the above could also refer to a
project or
namespace
if the image is being stored in an OpenShift Container Platform environment with an internal
registry (the OpenShift Container Registry).
OpenShift Container Platform provides the oc tag command, which is similar to the docker
tag command, but operates on image streams instead of directly on images.
|
See Red Hat enterprise Linux 7’s
Getting
Started with Containers documentation for more about tagging images directly
using the |
Adding Tags to Image Streams
Keeping in mind that an image stream in OpenShift Container Platform comprises zero or more
container images identified by tags, you can add tags to an image stream using the
oc tag command:
$ oc tag <source> <destination>
For example, to configure the ruby imagestream’s static-2.0 tag to always refer to the current image for the ruby imagestream’s 2.0 tag:
$ oc tag ruby:2.0 ruby:static-2.0
This creates a new imagestream tag named static-2.0 in the ruby imagestream. The
new tag directly reference the image id that the ruby:2.0 imagestream tag pointed
to at the time oc tag was run, and the image it points to never changes.
There are different types of tags available. The default behavior uses a permanent tag, which points to a specific image in time; even when the source changes, the new (destination) tag does not change.
A tracking tag means the destination tag’s metadata is updated during
the import of the source tag. To ensure the destination tag is updated whenever the
source tag changes, use the --alias=true flag:
$ oc tag --alias=true <source> <destination>
You can also add the --scheduled=true flag to have the destination tag be
refreshed (i.e., re-imported) periodically. The period is configured globally at
the system level.
See Importing Tag and Image Metadata for more details.
If you want to instruct Docker to always fetch the tagged image from the
integrated registry, use --reference-policy=local. The registry uses the
pull-through feature
to serve the image to the client. By default, the image blobs are
mirrored locally by the registry. As a result, they can be pulled more quickly
the next time they are needed. The flag also allows for pulling from
insecure registries without a need to supply --insecure-registry to the Docker
daemon as long as the image stream has an insecure annotation
or the tag has an insecure import policy.
Recommended Tagging Conventions
Images evolve over time and their tags reflect this. An image tag always points to the latest image built.
If there is too much information embedded in a tag name (for example,
v2.0.1-may-2016), the tag points to just one revision of an image and is
never updated. Using default image pruning options, such an image is never
removed.
In very large clusters, the schema of creating new tags for every revised image
could eventually fill up the etcd datastore with excess tag metadata for images
that are long outdated.
Instead, if the tag is named v2.0, more image revisions are more likely. This
results in longer
tag history and, therefore, the image pruner is more likely to remove old and unused images.
Refer to Pruning Images for more information.
Although tag naming convention is up to you, here are a few examples in the
format <image_name>:<image_tag>:
| Description | example |
|---|---|
Revision |
|
Architecture |
|
Base image |
|
Latest (potentially unstable) |
|
Latest stable |
|
If you require dates in tag names, periodically inspect old and unsupported
images and istags and remove them. Otherwise, you might experience increasing
resource usage caused by old images.
Removing Tags from Image Streams
To remove a tag completely from an image stream run:
$ oc delete istag/ruby:latest
or:
$ oc tag -d ruby:latest
Referencing Images in Image Streams
Images can be referenced in image streams using the following reference types:
-
An
ImageStreamTagis used to reference or retrieve an image for a given image stream and tag. It uses the following convention for its name:<image_stream_name>:<tag>
-
An
ImageStreamImageis used to reference or retrieve an image for a given image stream and image name. It uses the following convention for its name:<image_stream_name>@<id>
The
<id>is an immutable identifier for a specific image, also called a digest. -
A
DockerImageis used to reference or retrieve an image for a given external registry. It uses standard Docker pull specification for its name, e.g.:openshift/ruby-20-centos7:2.0
When no tag is specified, it is assumed the latest tag is used.
You can also reference a third-party registry:
registry.access.redhat.com/rhel7:latest
Or an image with a digest:
centos/ruby-22-centos7@sha256:3a335d7d8a452970c5b4054ad7118ff134b3a6b50a2bb6d0c07c746e8986b28e
When viewing example image stream definitions, such as the
example
CentOS image streams, you may notice they contain definitions of
ImageStreamTag and references to DockerImage, but nothing related to
ImageStreamImage.
This is because the ImageStreamImage objects are automatically created in
OpenShift Container Platform whenever you import or tag an image into the image stream. You
should never have to explicitly define an ImageStreamImage object in any
image stream definition that you use to create image streams.
You can view an image’s object definition by retrieving an ImageStreamImage
definition using the image stream name and ID:
$ oc export isimage <image_stream_name>@<id>
|
You can find valid $ oc describe is <image_stream_name> |
For example, from the ruby image stream asking for the ImageStreamImage
with the name and ID of ruby@3a335d7:
example 1. Definition of an Image Object Retrieved via ImageStreamImage
$ oc export isimage ruby@3a335d7
apiVersion: v1
image:
dockerImageLayers:
- name: sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
size: 0
- name: sha256:ee1dd2cb6df21971f4af6de0f1d7782b81fb63156801cfde2bb47b4247c23c29
size: 196634330
- name: sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
size: 0
- name: sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
size: 0
- name: sha256:ca062656bff07f18bff46be00f40cfbb069687ec124ac0aa038fd676cfaea092
size: 177723024
- name: sha256:63d529c59c92843c395befd065de516ee9ed4995549f8218eac6ff088bfa6b6e
size: 55679776
dockerImageMetadata:
Architecture: amd64
Author: SoftwareCollections.org <sclorg@redhat.com>
Config:
Cmd:
- /bin/sh
- -c
- $STI_SCRIPTS_PATH/usage
entrypoint:
- container-entrypoint
env:
- PATH=/opt/app-root/src/bin:/opt/app-root/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
- STI_SCRIPTS_URL=image:///usr/libexec/s2i
- STI_SCRIPTS_PATH=/usr/libexec/s2i
- HOMe=/opt/app-root/src
- BASH_eNV=/opt/app-root/etc/scl_enable
- eNV=/opt/app-root/etc/scl_enable
- PROMPT_COMMAND=. /opt/app-root/etc/scl_enable
- RUBY_VeRSION=2.2
exposedPorts:
8080/tcp: {}
Image: d9c3abc5456a9461954ff0de8ae25e0e016aad35700594714d42b687564b1f51
Labels:
build-date: 2015-12-23
io.k8s.description: Platform for building and running Ruby 2.2 applications
io.k8s.display-name: Ruby 2.2
io.openshift.builder-base-version: 8d95148
io.openshift.builder-version: 8847438ba06307f86ac877465eadc835201241df
io.openshift.s2i.scripts-url: image:///usr/libexec/s2i
io.openshift.tags: builder,ruby,ruby22
io.s2i.scripts-url: image:///usr/libexec/s2i
license: GPLv2
name: CentOS Base Image
vendor: CentOS
User: "1001"
WorkingDir: /opt/app-root/src
ContainerConfig: {}
Created: 2016-01-26T21:07:27Z
DockerVersion: 1.8.2-el7
Id: 57b08d979c86f4500dc8cad639c9518744c8dd39447c055a3517dc9c18d6fccd
Parent: d9c3abc5456a9461954ff0de8ae25e0e016aad35700594714d42b687564b1f51
Size: 430037130
apiVersion: "1.0"
kind: DockerImage
dockerImageMetadataVersion: "1.0"
dockerImageReference: centos/ruby-22-centos7@sha256:3a335d7d8a452970c5b4054ad7118ff134b3a6b50a2bb6d0c07c746e8986b28e
metadata:
creationTimestamp: 2016-01-29T13:17:45Z
name: sha256:3a335d7d8a452970c5b4054ad7118ff134b3a6b50a2bb6d0c07c746e8986b28e
resourceVersion: "352"
uid: af2e7a0c-c68a-11e5-8a99-525400f25e34
kind: ImageStreamImage
metadata:
creationTimestamp: null
name: ruby@3a335d7
namespace: openshift
selflink: /oapi/v1/namespaces/openshift/imagestreamimages/ruby@3a335d7
Image Pull Policy
each container in a pod has a container image. Once you have created an image and pushed it to a registry, you can then refer to it in the pod.
When OpenShift Container Platform creates containers, it uses the container’s
imagePullPolicy to determine if the image should be pulled prior to starting
the container. There are three possible values for imagePullPolicy:
-
Always- always pull the image. -
IfNotPresent- only pull the image if it does not already exist on the node. -
Never- never pull the image.
If a container’s imagePullPolicy
parameter is not specified, OpenShift Container Platform sets it based on the image’s tag:
-
If the tag is latest, OpenShift Container Platform defaults
imagePullPolicytoAlways. -
Otherwise, OpenShift Container Platform defaults
imagePullPolicytoIfNotPresent.
Accessing the Internal Registry
You can access OpenShift Container Platform’s internal registry directly to push or pull
images. For example, this could be helpful if you wanted to
create an image
stream by manually pushing an image, or just to docker pull an image
directly.
The internal registry authenticates using the same
tokens
as the OpenShift Container Platform API. To perform a docker login against the internal registry,
you can choose any user name and email, but the password must be a valid
OpenShift Container Platform token.
To log into the internal registry:
-
Log in to OpenShift Container Platform:
$ oc login
-
Get your access token:
$ oc whoami -t
-
Log in to the internal registry using the token. You must have docker installed on your system:
$ docker login -u <user_name> -e <email_address> \ -p <token_value> <registry_server>:<port>Contact your cluster administrator if you do not know the registry IP or host name and port to use.
In order to pull an image, the authenticated user must have get rights on the
requested imagestreams/layers. In order to push an image, the authenticated
user must have update rights on the requested imagestreams/layers.
By default, all service accounts in a project have rights to pull any image in the same project, and the builder service account has rights to push any image in the same project.
Using Image Pull Secrets
Docker registries can be secured to prevent unauthorized parties from accessing certain images. If you are using OpenShift Container Platform’s internal registry and are pulling from image streams located in the same project, then your pod’s service account should already have the correct permissions and no additional action should be required.
However, for other scenarios, such as referencing images across OpenShift Container Platform projects or from secured registries, then additional configuration steps are required. The following sections detail these scenarios and their required steps.
Allowing Pods to Reference Images Across Projects
When using the internal registry, to allow pods in project-a to reference
images in project-b, a service account in project-a must be bound to the
system:image-puller role in project-b:
$ oc policy add-role-to-user \
system:image-puller system:serviceaccount:project-a:default \
--namespace=project-b
After adding that role, the pods in project-a that reference the default service account is able to pull images from project-b.
To allow access for any service account in project-a, use the group:
$ oc policy add-role-to-group \
system:image-puller system:serviceaccounts:project-a \
--namespace=project-b
Allowing Pods to Reference Images from Other Secured Registries
The .dockercfg file (or $HOMe/.docker/config.json for newer Docker clients) is a Docker credentials file that stores your information if you have previously logged into a secured or insecure registry.
To pull a secured container image that is not from OpenShift Container Platform’s internal registry, you must create a pull secret from your Docker credentials and add it to your service account.
If you already have a .dockercfg file for the secured registry, you can create a secret from that file by running:
$ oc secrets new <pull_secret_name> .dockercfg=<path/to/.dockercfg>
Or if you have a $HOMe/.docker/config.json file:
$ oc secrets new <pull_secret_name> .dockerconfigjson=<path/to/.docker/config.json>
If you do not already have a Docker credentials file for the secured registry, you can create a secret by running:
$ oc secrets new-dockercfg <pull_secret_name> \
--docker-server=<registry_server> --docker-username=<user_name> \
--docker-password=<password> --docker-email=<email>
To use a secret for pulling images for pods, you must add the secret to your service account. The name of the service account in this example should match the name of the service account the pod uses; default is the default service account:
$ oc secrets link default <pull_secret_name> --for=pull
To use a secret for pushing and pulling build images, the secret must be mountable inside of a pod. You can do this by running:
$ oc secrets link builder <pull_secret_name>
Importing Tag and Image Metadata
An image stream can be configured to import tag and image metadata from an image repository in an external Docker image registry. You can do this using a few different methods.
-
You can manually import tag and image information with the
oc import-imagecommand using the--fromoption:$ oc import-image <image_stream_name>[:<tag>] --from=<docker_image_repo> --confirm
For example:
$ oc import-image my-ruby --from=docker.io/openshift/ruby-20-centos7 --confirm The import completed successfully. Name: my-ruby Created: Less than a second ago Labels: <none> Annotations: openshift.io/image.dockerRepositoryCheck=2016-05-06T20:59:30Z Docker Pull Spec: 172.30.94.234:5000/demo-project/my-ruby Tag Spec Created PullSpec Image latest docker.io/openshift/ruby-20-centos7 Less than a second ago docker.io/openshift/ruby-20-centos7@sha256:772c5bf9b2d1e8... <same>
You can also add the
--allflag to import all tags for the image instead of just latest. -
Like most objects in OpenShift Container Platform, you can also write and save a JSON or YAML definition to a file then create the object using the CLI. Set the
spec.dockerImageRepositoryfield to the Docker pull spec for the image:apiVersion: "v1" kind: "ImageStream" metadata: name: "my-ruby" spec: dockerImageRepository: "docker.io/openshift/ruby-20-centos7"
Then create the object:
$ oc create -f <file>
When you create an image stream that references an image in an external Docker registry, OpenShift Container Platform communicates with the external registry within a short amount of time to get up to date information about the image.
After the tag and image metadata is synchronized, the image stream object would look similar to the following:
apiVersion: v1
kind: ImageStream
metadata:
name: my-ruby
namespace: demo-project
selflink: /oapi/v1/namespaces/demo-project/imagestreams/my-ruby
uid: 5b9bd745-13d2-11e6-9a86-0ada84b8265d
resourceVersion: '4699413'
generation: 2
creationTimestamp: '2016-05-06T21:34:48Z'
annotations:
openshift.io/image.dockerRepositoryCheck: '2016-05-06T21:34:48Z'
spec:
dockerImageRepository: docker.io/openshift/ruby-20-centos7
tags:
-
name: latest
annotations: null
from:
kind: DockerImage
name: 'docker.io/openshift/ruby-20-centos7:latest'
generation: 2
importPolicy: { }
status:
dockerImageRepository: '172.30.94.234:5000/demo-project/my-ruby'
tags:
-
tag: latest
items:
-
created: '2016-05-06T21:34:48Z'
dockerImageReference: 'docker.io/openshift/ruby-20-centos7@sha256:772c5bf9b2d1e8e80742ed75aab05820419dc4532fa6d7ad8a1efddda5493dc3'
image: 'sha256:772c5bf9b2d1e8e80742ed75aab05820419dc4532fa6d7ad8a1efddda5493dc3'
generation: 2
You can set a tag to query external registries at a scheduled interval to
synchronize tag and image metadata by setting the --scheduled=true flag with
the oc tag command as mentioned in Adding Tags to Image
Streams.
Alternatively, you can set importPolicy.scheduled to true in the tag’s
definition:
apiVersion: v1
kind: ImageStream
metadata:
name: ruby
spec:
tags:
- from:
kind: DockerImage
name: openshift/ruby-20-centos7
name: latest
importPolicy:
scheduled: true
Importing Images from Insecure Registries
An image stream can be configured to import tag and image metadata from insecure image registries, such as those signed with a self-signed certificate or using plain HTTP instead of HTTPS.
To configure this, add the openshift.io/image.insecureRepository annotation
and set it to true. This setting bypasses certificate validation when
connecting to the registry:
kind: ImageStream
apiVersion: v1
metadata:
name: ruby
annotations:
openshift.io/image.insecureRepository: "true" (1)
spec:
dockerImageRepository: my.repo.com:5000/myimage| 1 | Set the openshift.io/image.insecureRepository annotation to true |
|
This option instructs integrated registry to fall back to an insecure transport
for any external image tagged in the image stream when serving it, which is
dangerous. If possible, avoid this risk by
marking just an |
|
The above definition only affects importing tag and image metadata. For this
image to be used in the cluster (e.g., to be able to do a
|
ImageStream Tag Policies
Insecure Tag Import Policy
The above annotation applies to all images and tags of a particular
ImageStream. For a finer-grained control, policies may be set on
istags.
Set importPolicy.insecure in the tag’s definition to true to allow a
fall-back to insecure transport just for images under this tag.
|
The fall-back to insecure transport for an image under particular |
Reference Policy
The Reference Policy allows you to specify where the image consumers pulls
from. It is only applicable to remote images (those imported from external
registries). There are two options to choose from, Local and Source.
The Source policy instructs clients to pull directly from the source registry
of the image. The integrated registry is not involved unless the image is
managed by the cluster. (It is not an external image.) This is the default
policy.
The Local policy instructs clients to always pull from the integrated
registry. This is useful if you want to pull from external insecure registries
without modifying Docker daemon settings.
The pull-through feature pull-through feature of the registry serves the remote image to the client. Additionally, all the blobs are mirrored for faster access later.
You can set the policy in a specification of image stream tag as
referencePolicy.type.
example 2. example of Insecure Tag with a Local Reference Policy
kind: ImageStream
apiVersion: v1
metadata:
name: ruby
tags:
- from:
kind: DockerImage
name: my.repo.com:5000/myimage
name: mytag
importPolicy:
insecure: true (1)
referencePolicy:
type: Local (2)| 1 | Set tag mytag to use an insecure connection to that registry. |
| 2 | Set tag mytag to use integrated registry for pulling external images. If
the reference policy type is set to Source, clients fetch the image
directly from my.repo.com:5000/myimage. |
Importing Images from Private Registries
An image stream can be configured to import tag and image metadata from private image registries, requiring authentication.
To configure this, you need to create a
secret, which is used to store
your credentials. See
Allowing
Pods to Reference Images from Other Secured Registries for instructions on
creating a secret using oc create secret command.
After the secret is configured, proceed with creating the new image stream or
using the oc import-image command. During the import process, OpenShift Container Platform
picks up the secrets and provide them to the remote party.
|
When importing from an insecure registry, the registry URL defined in the secret
must include the |
Adding Trusted Certificates for external Registries
If the registry you are importing from is using a certificate that is not signed by a standard certificate authority, you need to explicitly configure the system to trust the registry’s certificate or signing authority. This can be done by adding the CA certificate or registry certificate to the host system running the registry import controller (typically the master node).
The certificate or CA certificate must be added to /etc/pki/tls/certs or /etc/pki/ca-trust,
respectively, on the host system. The update-ca-trust command also needs to be
run on Red Hat distributions followed by a restart of the master service to pick up
the certificate changes.
Importing Images Across Projects
An image stream can be configured to import tag and image metadata from the
internal registry, but from a different project. The recommended method for
this is to use the oc tag command as shown in Adding Tags to
Image Streams:
$ oc tag <source_project>/<image_stream>:<tag> <new_image_stream>:<new_tag>
Another method is to import the image from the other project manually using the pull spec:
|
The following method is strongly discouraged and should be used only if the
former using |
-
First, add the necessary policy to access the other project:
$ oc policy add-role-to-group \ system:image-puller \ system:serviceaccounts:<destination_project> \ -n <source_project>This allows
<destination_project>to pull images from<source_project>. -
With the policy in place, you can import the image manually:
$ oc import-image <new_image_stream> --confirm \ --from=<docker_registry>/<source_project>/<image_stream>
Creating an Image Stream by Manually Pushing an Image
An image stream can also be automatically created by manually pushing an image to the internal registry. This is only possible when using an OpenShift Container Platform internal registry.
Before performing this procedure, the following must be satisfied:
-
The destination project you push to must already exist.
-
The user must be authorized to
{get, update} "imagestream/layers"in that project. In addition, since the image stream does not already exist, the user must be authorized to{create} "imagestream"in that project. If you are a project administrator, then you would have these permissions.
|
The system:image-pusher role does not grant permission to create new image streams, only to push images to existing image streams, so it cannot be used to push images to image streams that do not yet exist unless additional permissions are also granted to the user. |
To create an image stream by manually pushing an image:
-
First, log in to the internal registry.
-
Then, tag your image using the appropriate internal registry location. For example, if you had already pulled the docker.io/centos:centos7 image locally:
$ docker tag docker.io/centos:centos7 172.30.48.125:5000/test/my-image
-
Finally, push the image to your internal registry. For example:
$ docker push 172.30.48.125:5000/test/my-image The push refers to a repository [172.30.48.125:5000/test/my-image] (len: 1) c8a648134623: Pushed 2bf4902415e3: Pushed latest: digest: sha256:be8bc4068b2f60cf274fc216e4caba6aa845fff5fa29139e6e7497bb57e48d67 size: 6273
-
Verify that the image stream was created:
$ oc get is NAMe DOCKeR RePO TAGS UPDATeD my-image 172.30.48.125:5000/test/my-image latest 3 seconds ago
Writing Image Stream Definitions
You can define image streams by writing the image stream definition for the entire image stream. This allows you to distribute
the definition to different clusters without running oc commands.
An image stream definition specifies information about the image stream and the specific tags to be imported.
Definition of an Image Stream Object
apiVersion: v1
kind: ImageStream
metadata:
name: ruby
annotations:
openshift.io/display-name: Ruby (1)
spec:
tags:
- name: '2.0' (2)
annotations:
openshift.io/display-name: Ruby 2.0 (3)
description: >- (4)
Build and run Ruby 2.0 applications on CentOS 7. For more information
about using this builder image, including OpenShift considerations,
see
https://github.com/sclorg/s2i-ruby-container/tree/master/2.0/ReADMe.md.
iconClass: icon-ruby (5)
sampleRepo: 'https://github.com/sclorg/ruby-ex.git' (6)
tags: 'builder,ruby' (7)
version: '2.0' (8)
from:
kind: DockerImage (10)
name: 'docker.io/openshift/ruby-20-centos7:latest' (11)
| 1 | A brief, user-friendly name for the whole image stream. |
| 2 | The tag is referred to as the version. Tags appear in a drop-down menu. |
| 3 | A user-friendly name for this tag within the image stream. This should be brief and include version information when appropriate. |
| 4 | A description of the tag, which includes enough detail for users to understand what the image is providing. It can include links to additional instructions. Limit the description to a few sentences. |
| 5 | The icon to show for this tag. Pick from our existing logo icons when possible. Icons from FontAwesome and Patternfly can also be used. Alternatively, provide icons through CSS customizations that can be added to an OpenShift Container Platform cluster that uses your image stream. You must specify an icon class that exists, or it prevents falling back to the generic icon. |
| 6 | A URL to a source repository that works with this builder image tag and results in a sample running application. |
| 7 | Categories that the image stream tag is associated with. The builder tag is
required for it to show up in the catalog. Add tags that associates it with one
of the provided catalog categories. Refer to the id and categoryAliases in
CATALOG_CATeGORIeS in the console’s
constants
file. The categories can also be
customized
for the whole cluster. |
| 8 | Languages this image supports. This value is used during oc new-app invocations to try to match potential
builder images to the provided source repository. |
| 9 | Version information for this tag. |
| 10 | The type of object this image stream tag is referencing. Valid values are: DockerImage, ImageStreamTag, and ImageStreamImage. |
| 11 | The object this image stream tag imports. |