什么是ImageStream
Image Stream是OpenShift中的一种对象，它并不是用来存储Image的，而是用来记录并管理Image信息的。它就像是所有Image的虚拟视图，可以通过它访问存放在不同Image Registry（OpenShift外部独立运行的Registry、或是OpenShift内置的Registry）上的Image。通过这个视图可以简化对那些来自不同Registry的Image的访问。Image Stream中会记录需要访问的Image的访问标识（Image Stream Tag），并通过指针（Image Stream Image）记录它们的实际保存位置，其中指向Image的指针是由Image Stream name和Image ID构成的。
根据Image Stream所在项目，可将其分为集群级和项目级的Image Stream。无论当前在哪个项目中，任何用户都可访问到集群级的Image Stream；而项目级Image Stream只能该项目用户或被授权用户才可访问。
从Image生成ImageStream
如果我们跟随《OpenShift 4 Hands-on Lab (1) - 部署应用》成功创建应用后可以通过以下命令发现OpenShift会自动生成ImageStream对象，这就说明在运行应用前，OpenShift要创建ImageStream并建立App Image的指向关系。
oc get is
OpenShift除了可以自动创建ImageStream外，我们还可以从定义ImageStream的YAML文件创建它，但是我们通常用以下两种方法手工从Image生成ImageStream：
- 首选创建名为imagestream-lab1的OpenShift项目，以下所有操作都缺省在该项目中进行。
$ oc new-project imagestream-lab1
- 通过import-image导入镜像的信息并生成ImageStream。以下将docker.io/openshift/deployment-example:v1的镜像信息导入到名为is-example的ImageStream中，并用v1指向该远程镜像。
$ oc import-image --from=docker.io/openshift/deployment-example:v1 is-example:v1 --confirm
Name: is-example
Namespace: imagestream-lab1
Created: Less than a second ago
Labels: <none>
Annotations: openshift.io/image.dockerRepositoryCheck=2020-02-02T04:27:15Z
Image Repository: image-registry.openshift-image-registry.svc:5000/imagestream-lab1/is-example
Image Lookup: local=false
Unique Images: 1
Tags: 1
v1
tagged from docker.io/openshift/deployment-example:v1
** docker.io/openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
Less than a second ago
Image Name: is-example:v1
Docker Image: docker.io/openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
Name: sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
Created: Less than a second ago
Annotations: image.openshift.io/dockerLayersOrder=ascending
Image Size: 5.77MB in 6 layers
Layers: 0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
5.77MB sha256:50438f3701c47319ff1c8189ff19f5a8c779f2479aa2066979b930c7dbb3bde8
0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
Image Created: 4 years ago
Author: Clayton Coleman <ccoleman@redhat.com>
Arch: amd64
Entrypoint: /deployment v1
Working Dir: <none>
User: <none>
Exposes Ports: 8080/tcp
Docker Labels: <none>
Environment: COLOR=#006e9c
- 通过tag对执行镜像打标签。下面是将docker上的openshift/deployment-example:v2打标签为v2，并保存到名为is-example的ImageStream中。
$ oc tag --source=docker openshift/deployment-example:v2 is-example:v2
Tag is-example:v2 set to openshift/deployment-example:v2.
ImageStream的操作
- 查看ImageStream列表
$ oc get is
NAME IMAGE REPOSITORY TAGS UPDATED
is-example default-route-openshift-image-registry.apps.cluster-beijing-c70a.beijing-c70a.example.opentlc.com/imagestream-lab1/is-example v2,v1 9 minutes ag
- 查看ImageStream配置
Name: is-example
Namespace: imagestream-lab1
Created: 12 minutes ago
Labels: <none>
Annotations: openshift.io/image.dockerRepositoryCheck=2020-02-02T04:33:29Z
Image Repository: default-route-openshift-image-registry.apps.cluster-beijing-c70a.beijing-c70a.example.opentlc.com/imagestream-lab1/is-example
Image Lookup: local=false
Unique Images: 2
Tags: 2
v1
tagged from docker.io/openshift/deployment-example:v1
**. docker.io/openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
12 minutes ago
v2
tagged from openshift/deployment-example:v2
**. openshift/deployment-example@sha256:1318f08b141aa6a4cdca8c09fe8754b6c9f7802f8fc24e4e39ebf93e9d58472b
12 minutes ago
- 查看ImageStreamTag列表
$ oc get istag
NAME IMAGE REF UPDATED
is-example:v1 docker.io/openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b 10 minutes ago
is-example:v2 openshift/deployment-example@sha256:1318f08b141aa6a4cdca8c09fe8754b6c9f7802f8fc24e4e39ebf93e9d58472b 10 minutes ago
- 查看ImageStreamTag配置
$ oc describe istag is-example:v1
Image Name: sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
Docker Image: docker.io/openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
Name: sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
Created: 2 hours ago
Annotations: image.openshift.io/dockerLayersOrder=ascending
Image Size: 5.77MB in 6 layers
Layers: 0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
5.77MB sha256:50438f3701c47319ff1c8189ff19f5a8c779f2479aa2066979b930c7dbb3bde8
0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
0B sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
Image Created: 4 years ago
Author: Clayton Coleman <ccoleman@redhat.com>
Arch: amd64
Entrypoint: /deployment v1
Working Dir: <none>
User: <none>
Exposes Ports: 8080/tcp
Docker Labels: <none>
Environment: COLOR=#006e9c
- 按大小排序查看imagestream-lab1项目中的imagestreams
$ oc adm top imagestreams -n imagestream-lab1
NAME STORAGE IMAGES LAYERS
imagestream-lab1/is-example 5.503MiB 2 12
- 执行命令，将“is-example:v1”指向“docker openshift/deployment-example:v2”
$ oc tag --source=docker openshift/deployment-example:v2 is-example:v1
- 查看is-example，其中v1的指向的ImageStreamImage记录为2条，当前v1和v2指向的是同一个Image。而v1以前指向的是另一个Image。
$ oc describe is is-example
Name: is-example
Namespace: imagestream-lab1
Created: 4 minutes ago
Labels: <none>
Annotations: openshift.io/image.dockerRepositoryCheck=2020-02-02T14:07:48Z
Image Repository: default-route-openshift-image-registry.apps.cluster-beijing-c70a.beijing-c70a.example.opentlc.com/imagestream-lab1/is-example
Image Lookup: local=false
Unique Images: 2
Tags: 2
v1
tagged from openshift/deployment-example:v2
* openshift/deployment-example@sha256:1318f08b141aa6a4cdca8c09fe8754b6c9f7802f8fc24e4e39ebf93e9d58472b
About a minute ago
docker.io/openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
4 minutes ago
v2
tagged from openshift/deployment-example:v2
* openshift/deployment-example@sha256:1318f08b141aa6a4cdca8c09fe8754b6c9f7802f8fc24e4e39ebf93e9d58472b
3 minutes ago
生成ImageStream过程的选项
在使用“oc tag”和“oc import-image”命令生成ImageStream的时候，可以使用参数“–reference-policy=local”让OpenShift只在本地（其内部的Image Registry）找镜像；另外还可以用“–reference”参数让OpenShift只创建一个非导入的ImageStreamTag，即不导入目标Image的元数据。下面我们看看这两个选项对ImageStream有什么影响？
- 新建imagestream-lab2项目。
$ oc new-project imagestream-lab2
- 执行以下命令，使用不同选项生从“openshift/deployment-example:v1”成相关ImageStream资源。
$ oc tag --source=docker openshift/deployment-example:v1 is-example:v1
$ oc tag --source=docker openshift/deployment-example:v1 is-example:v2 --reference-policy=local
$ oc tag --source=docker openshift/deployment-example:v1 is-example:v3 --reference=true
- 查看ImageStream的信息，注意3个Tags它们之间的差异，其中v3没有相应的镜像ID（说明当使用–reference=true，OpenShift不会主动获取镜像元数据）。
$ oc describe is is-example
Name: is-example
Namespace: imagestream-lab2
Created: 2 minutes ago
Labels: <none>
Annotations: openshift.io/image.dockerRepositoryCheck=2020-02-02T11:14:02Z
Image Repository: default-route-openshift-image-registry.apps.cluster-beijing-c70a.beijing-c70a.example.opentlc.com/imagestream-lab2/is-example
Image Lookup: local=false
Unique Images: 2
Tags: 3
v1
tagged from openshift/deployment-example:v1
** openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
2 minutes ago
v2
tagged from openshift/deployment-example:v1
prefer registry pullthrough when referencing this tag
** openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b
2 minutes ago
v3
reference to registry openshift/deployment-example:v1
** openshift/deployment-example:v1
2 minutes ago
- 查看ImageStreamTag列表，确认没有“is-example:v3”，说明它是无效的。
$ oc get istag
NAME IMAGE REF UPDATED
is-example:v1 openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b 2 minutes ago
is-example:v2 image-registry.openshift-image-registry.svc:5000/imagestream-lab2/is-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b 2 minutes ago
- 在OpenShift控制台也可看出“is-example:v3”的错误提示。
- 执行以下命令，根据已有的ImageSteamTag生成新的ImageSteamTag，这次使用了“–reference=true”参数。
oc tag --source=istag is-example:v1 is-example:v4 --reference=true
- 再次查看ImageStreamTag，确认“is-example:v4”是正常的。虽然这次使用了“–reference=true”参数，即OpenShift不会主动获取镜像元数据，但是这些信息已经在本地有了（是在创建“is-example:v1”的步骤有的）。
$ oc get istag
NAME IMAGE REF UPDATED
is-example:v1 openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b 22 minutes ago
is-example:v2 image-registry.openshift-image-registry.svc:5000/imagestream-lab2/is-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b 22 minutes ago
is-example:v4 openshift/deployment-example@sha256:c505b916f7e5143a356ff961f2c21aee40fbd2cd906c1e3feeb8d5e978da284b About a minute ago
常见问题
- 根据远程的Image创建ImageStream的时候，Image是否会下载到本地？
说明：不会。只有第一次基于这个Image运行应用的时候才去下载这个Image。 - 当使用“–reference-policy=local”参数和不使用它的时候，对使用Image有什么影响？
说明：当使用“–reference-policy=local”后，OpenShift就不会访问其外部的Registry获得Image了，只会使用其内置的Registry获取Image了。因此需要手动将Image提前push到其内置的Registry才可 使用这些Image。 - 删除了ImageStreamTag后，对应的本地Image有影响么？
说明：没有。两者是若关联关系，删除任何一个不会自动删除相关的另一方。
来源：CSDN
作者：dawnsky.liu
链接：https://blog.csdn.net/weixin_43902588/article/details/104138965