一步步学KubeVirt CI （2） - 镜像构建
空镜像scratch
scratch是一个空镜像，直接docker hub下载是下不了的，只能在Dockerfile中用FROM
# 不用容器，先用go build & run 执行下看下结果[root@localhost hello]# cat app.go package mainimport "fmt"func main(){
fmt.Printf("Hello World!");}[root@localhost hello]# go build app.go [root@localhost hello]# lsapp app.go[root@localhost hello]# ./app Hello World![root@localhost hello]## Dockerfile （使用了空镜像scratch）[root@localhost hello]# cat DockerfileFROM scratch
ADD app /
CMD ["/app"]# 构建镜像[root@localhost hello]# docker build -t hello .Emulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
STEP 1/3: FROM scratch
STEP 2/3: ADD app /
--> f40b810d4f1
STEP 3/3: CMD ["/app"]COMMIT hello
--> 3b05b3e8edb
Successfully tagged localhost/hello:latest
3b05b3e8edb740b20ed133aa65539217efe8cf2e97816b2912992fb8edb73f6b[root@localhost hello]# docker imagesEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/hello latest 3b05b3e8edb7 3 seconds ago 1.78 MB# 用容器跑的结果 和 不用容器，用go build & run 一致[root@localhost hello]# docker container run -it helloEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
Hello World![root@localhost hello]#虚悬镜像
[root@localhost hello]# docker system dfEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
TYPE TOTAL ACTIVE SIZE RECLAIMABLE
Images 21 5 19.44GB 4.2GB (22%)Containers 10 4 823B 60B (7%)Local Volumes 8 7 23.07GB 22.47GB (97%)[root@localhost hello]# docker imagesEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/hello 2 a37976309a63 16 seconds ago 7.59 MB<none> <none> 19be39c07a76 27 seconds ago 340 MB
localhost/hello latest 3b05b3e8edb7 19 minutes ago 1.78 MB<none> <none> 573a101bae9d 24 minutes ago 29.4 kB
quay.io/kubevirtci/k8s-1.21 2207060141-111fd50 6fa0fcc42f47 31 hours ago 15.2 GB
quay.io/kubevirtci/gocli 2207060141-111fd50 07874ec90d6e 31 hours ago 14.5 MB
quay.io/kubevirt/builder 2206141426-2d31aa580 7ae2a103287f 3 weeks ago 1.98 GB
docker.io/library/golang alpine 155ead2e66ca 5 weeks ago 338 MB
docker.io/library/alpine latest e66264b98777 6 weeks ago 5.82 MB
docker.io/kubevirtci/gocli latest 094672b6ef8e 21 months ago 12.6 MB
quay.io/libpod/registry 2.7 2d4f4b5309b1 2 years ago 26.8 MB
docker.io/backendcloud/example-hook-sidecar mybuild5 0581e298f5bb 52 years ago 211 MB
docker.io/backendcloud/winrmcli mybuild4 91ca4390f858 52 years ago 199 MB
docker.io/backendcloud/winrmcli mybuild5 91ca4390f858 52 years ago 199 MB
docker.io/backendcloud/example-hook-sidecar mybuild6 0581e298f5bb 52 years ago 211 MB上面的镜像列表中，还可以看到一个特殊的镜像，这个镜像既没有仓库名，也没有标签，均为 <none>。
这个镜像原本是有镜像名和标签的，随着官方镜像维护，发布了新版本后，重新 docker pull 时，这个镜像名被转移到了新下载的镜像身上，而旧的镜像上的这个名称则被取消，从而成为了 <none>。除了 docker pull 可能导致这种情况，docker build 也同样可以导致这种现象。由于新旧镜像同名，旧镜像名称被取消，从而出现仓库名、标签均为 <none> 的镜像。这类无标签镜像也被称为 虚悬镜像(dangling image) ，可以用下面的命令专门显示这类镜像：
[root@localhost hello]# docker images ls -f dangling=trueEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
Error: cannot specify an image and a filter(s)#注意：不是images，是image，和docker images命令不同[root@localhost hello]# docker image ls -f dangling=trueEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
REPOSITORY TAG IMAGE ID CREATED SIZE<none> <none> 19be39c07a76 16 hours ago 340 MB<none> <none> 573a101bae9d 16 hours ago 29.4 kB一般来说，虚悬镜像已经失去了存在的价值，是可以随意删除的，可以用下面的命令删除。
[root@localhost hello]# docker image pruneEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
WARNING! This command removes all dangling images.
Are you sure you want to continue? [y/N] y
19be39c07a766503753c91261bfd2dd786f536db69402ccbc12bdaea054e3047
6220efe05008da6279e95d7a377993b035e59833dfd75f66184a24fcf2c8a85d
906f367739194e499b1baf1459fa7c0eca2cf8249fc466e671315c1f2a13b369[root@localhost hello]# docker image ls -f dangling=trueEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
REPOSITORY TAG IMAGE ID CREATED SIZE<none> <none> 573a101bae9d 16 hours ago 29.4 kB[root@localhost hello]# docker image ls -f dangling=trueEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
REPOSITORY TAG IMAGE ID CREATED SIZE<none> <none> 573a101bae9d 16 hours ago 29.4 kB[root@localhost hello]# docker imagesEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/hello 2 a37976309a63 16 hours ago 7.59 MB
localhost/hello latest 3b05b3e8edb7 16 hours ago 1.78 MB<none> <none> 573a101bae9d 16 hours ago 29.4 kB
quay.io/kubevirtci/k8s-1.21 2207060141-111fd50 6fa0fcc42f47 47 hours ago 15.2 GB
quay.io/kubevirtci/gocli 2207060141-111fd50 07874ec90d6e 2 days ago 14.5 MB
quay.io/kubevirt/builder 2206141426-2d31aa580 7ae2a103287f 3 weeks ago 1.98 GB
docker.io/library/golang alpine 155ead2e66ca 5 weeks ago 338 MB
docker.io/library/alpine latest e66264b98777 6 weeks ago 5.82 MB
docker.io/kubevirtci/gocli latest 094672b6ef8e 21 months ago 12.6 MB
quay.io/libpod/registry 2.7 2d4f4b5309b1 2 years ago 26.8 MB
docker.io/backendcloud/winrmcli mybuild4 91ca4390f858 52 years ago 199 MB
docker.io/backendcloud/winrmcli mybuild5 91ca4390f858 52 years ago 199 MB
docker.io/backendcloud/example-hook-sidecar mybuild6 0581e298f5bb 52 years ago 211 MB
docker.io/backendcloud/example-hook-sidecar mybuild5 0581e298f5bb 52 years ago 211 MB# 发现还有一个虚悬镜像，再删了一遍，还是没删掉，用docker rmi删除，提示有容器在使用该镜像。docker image prune这里做得不友好，一点warning信息没有。[root@localhost hello]# docker image pruneEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
WARNING! This command removes all dangling images.
Are you sure you want to continue? [y/N] y[root@localhost hello]# docker imagesEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/hello 2 a37976309a63 16 hours ago 7.59 MB
localhost/hello latest 3b05b3e8edb7 16 hours ago 1.78 MB<none> <none> 573a101bae9d 16 hours ago 29.4 kB
quay.io/kubevirtci/k8s-1.21 2207060141-111fd50 6fa0fcc42f47 47 hours ago 15.2 GB
quay.io/kubevirtci/gocli 2207060141-111fd50 07874ec90d6e 2 days ago 14.5 MB
quay.io/kubevirt/builder 2206141426-2d31aa580 7ae2a103287f 3 weeks ago 1.98 GB
docker.io/library/golang alpine 155ead2e66ca 5 weeks ago 338 MB
docker.io/library/alpine latest e66264b98777 6 weeks ago 5.82 MB
docker.io/kubevirtci/gocli latest 094672b6ef8e 21 months ago 12.6 MB
quay.io/libpod/registry 2.7 2d4f4b5309b1 2 years ago 26.8 MB
docker.io/backendcloud/winrmcli mybuild4 91ca4390f858 52 years ago 199 MB
docker.io/backendcloud/winrmcli mybuild5 91ca4390f858 52 years ago 199 MB
docker.io/backendcloud/example-hook-sidecar mybuild6 0581e298f5bb 52 years ago 211 MB
docker.io/backendcloud/example-hook-sidecar mybuild5 0581e298f5bb 52 years ago 211 MB[root@localhost hello]# docker rmi 573a101bae9dEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
Error: Image used by 095dff22c8f728ba34ead410db4c8a61b94f4e1119d7b9ec8c0d53140998e158: image is in use by a container多阶段构建
构建镜像和运行镜像分开，有两个好处
- 镜像很小
- 源代码分离，安全
# 多阶段构建Dockerfile[root@localhost hello]# cat Dockerfile FROM golang:alpine as builder
WORKDIR /go/src/
COPY app.go .RUN go build -o app app.go
FROM alpine:latest as prod
WORKDIR /root/
COPY --from=0 /go/src/app .CMD ["./app"]# 生成镜像（第一个跑完会被自动销毁，只保留第二个镜像）[root@localhost hello]# docker build -t hello:2 .Emulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.[1/2] STEP 1/4: FROM golang:alpine AS builder[1/2] STEP 2/4: WORKDIR /go/src/
--> Using cache 906f367739194e499b1baf1459fa7c0eca2cf8249fc466e671315c1f2a13b369
--> 906f3677391[1/2] STEP 3/4: COPY app.go .--> Using cache 6220efe05008da6279e95d7a377993b035e59833dfd75f66184a24fcf2c8a85d
--> 6220efe0500[1/2] STEP 4/4: RUN go build -o app app.go
--> 19be39c07a7[2/2] STEP 1/4: FROM alpine:latest AS prod
Resolved "alpine" as an alias (/etc/containers/registries.conf.d/000-shortnames.conf)Trying to pull docker.io/library/alpine:latest...
Getting image source signatures
Copying blob 2408cc74d12b skipped: already exists
Copying config e66264b987 done Writing manifest to image destination
Storing signatures[2/2] STEP 2/4: WORKDIR /root/
--> 9f975764a6d[2/2] STEP 3/4: COPY --from=0 /go/src/app .--> 22fd24c9b9d[2/2] STEP 4/4: CMD ["./app"][2/2] COMMIT hello:2
--> a37976309a6
Successfully tagged localhost/hello:2
a37976309a6375e3107bf0c89cc373d6c0b953b6596238006aabf0ac3bcfa762[root@localhost hello]# docker imagesEmulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/hello 2 a37976309a63 16 seconds ago 7.59 MB[root@localhost hello]# docker container run -it hello:2Emulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
Hello World![root@localhost hello]# # 镜像运行符合预期（将镜像从alpine换成上一小节的scratch空镜像也可以）本文参与 腾讯云自媒体同步曝光计划，分享自微信公众号。
原始发表：2022-07-13，如有侵权请联系 cloudcommunity@tencent.com 删除
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