Docker镜像列表中的none:none是什么

华为云 2022-09-23 09:22:49 阅读数:317

docker镜像是什么列表

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本篇概览

  • 在构建过Docker镜像的电脑上查看本地镜像列表,有可能看到下图红框中的镜像,在列表中展示为<none>:<none>
    在这里插入图片描述

  • 这种镜像在Docker官方文档中被称作dangling images,指的是没有标签并且没有被容器使用的镜像。

官方解释

怎么来的

  • 结合第一幅图,梳理一下dangling images怎么产生的:
  1. 第一次构建镜像时生成的镜像ID为079dbd67f9f4,此镜像会被构建工具加上标签bolingcavalry/eureka-server:0.0.1-SNAPSHOT;
  2. 第二次构建镜像时生成的镜像ID为e40a97f764ef,此镜像会被构建工具加上标签bolingcavalry/eureka-server:0.0.1-SNAPSHOT,
  3. Docker会移除079dbd67f9f4的标签,此时079dbd67f9f4就变成了dangling images,在镜像列表中展示为<none>:<none>

准备实战

  • 接下来通过实际操作来复现此问题,并做一些有趣的测试;

  • 操作的主要内容是将一个maven工程构建成Docker镜像,以下是环境信息:

  1. 操作系统:Ubuntu 18.04.2 LTS
  2. Docker:18.06.1-ce
  3. Java:1.8.0_191
  4. Maven:3.6.0

实战源码下载

  • 如果您不想写代码,也可以在Github下载整个maven工程,地址和链接信息如下表所示:
名称链接备注
项目主页https://github.com/zq2599/blog_demos该项目在GitHub上的主页
git仓库地址(https)https://github.com/zq2599/blog_demos.git该项目源码的仓库地址,https协议
git仓库地址(ssh)[email protected]:zq2599/blog_demos.git该项目源码的仓库地址,ssh协议
  • 这个git项目中有多个文件夹,本章源码在springcloudscaledemo这个文件夹下,如下图红框所示:
    在这里插入图片描述

  • springcloudscaledemo文件夹内有三个工程,本次实战用到的是eureka-server,如下图:
    在这里插入图片描述

实战操作

  • 接下来一起开发一个简单的java项目:

  • 基于Maven创建一个springboot工程,pom.xml内容如下,主要注意plugins节点中的插件,该插件是用来构建镜像的:

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.bolingcavalry</groupId> <artifactId>eureka-server</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>eureka-server</name> <description>Demo project for Spring Boot</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.5.9.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> <spring-cloud.version>Edgware.SR1</spring-cloud.version> </properties> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-eureka-server</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> </dependencies> <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>${spring-cloud.version}</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> <!--新增的docker maven插件--> <plugin> <groupId>com.spotify</groupId> <artifactId>docker-maven-plugin</artifactId> <version>0.4.12</version> <!--docker镜像相关的配置信息--> <configuration> <!--镜像名,这里用工程名--> <imageName>bolingcavalry/${project.artifactId}</imageName> <!--TAG,这里用工程版本号--> <imageTags> <imageTag>${project.version}</imageTag> </imageTags> <!--镜像的FROM,使用java官方镜像--> <baseImage>java:8u111-jdk</baseImage> <!--该镜像的容器启动后,直接运行spring boot工程--> <entryPoint>["java", "-jar", "/${project.build.finalName}.jar"]</entryPoint> <!--构建镜像的配置信息--> <resources> <resource> <targetPath>/</targetPath> <directory>${project.build.directory}</directory> <include>${project.build.finalName}.jar</include> </resource> </resources> </configuration> </plugin> </plugins> </build></project>
  • application.properties内容如下,可见该应用其实就是springcloud中的eureka身份:
server.port=8080eureka.instance.hostname=localhosteureka.client.register-with-eureka=falseeureka.client.fetch-registry=falseeureka.client.serviceUrl.defaultZone=http://${eureka.instance.hostname}:${server.port}/eureka/
  • 启动类是EurekaServerApplication,内容如下:
@SpringBootApplication@EnableEurekaServerpublic class EurekaServerApplication { public static void main(String[] args) { SpringApplication.run(EurekaServerApplication.class, args); }}
  • 现在工程已经创建好了,可以开始构建了;

构建镜像

  • 在pom.xml所在目录执行以下命令即可构建镜像:
mvn clean package -U -DskipTests docker:dockerBuild
  • 构建成功后,用docker images命令查看本地镜像列表如下,新增了ID为90b736eb388e的镜像:
[INFO] Built bolingcavalry/eureka-server[INFO] Tagging bolingcavalry/eureka-server with 0.0.1-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 10.918 s[INFO] Finished at: 2019-06-01T08:36:59Z[INFO] -------------[email protected]hedy:/home/willzhao/temp/201906/01/eureka-server# docker imagesREPOSITORY TAG IMAGE ID CREATED SIZEbolingcavalry/eureka-server 0.0.1-SNAPSHOT 90b736eb388e 5 seconds ago 683MBbolingcavalry/eureka-server latest 90b736eb388e 5 seconds ago 683MBjava 8u111-jdk d23bdf5b1b1b 2 years ago 643MB
  • 再次执行命令mvn clean package -U -DskipTests docker:build,也就是再构建一次;
  • 构建完成后查看镜像列表,ID为90b736eb388e的镜像已经成为dangling images,标签bolingcavalry/eureka-server:0.0.1-SNAPSHOT已经被新镜像be262f101e2c占有:
[INFO] Built bolingcavalry/eureka-server[INFO] Tagging bolingcavalry/eureka-server with 0.0.1-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 10.985 s[INFO] Finished at: 2019-06-01T08:44:49Z[INFO] -------------[email protected]hedy:/home/willzhao/temp/201906/01/eureka-server# docker imagesREPOSITORY TAG IMAGE ID CREATED SIZEbolingcavalry/eureka-server 0.0.1-SNAPSHOT be262f101e2c About a minute ago 683MBbolingcavalry/eureka-server latest be262f101e2c About a minute ago 683MB<none> <none> 90b736eb388e 9 minutes ago 683MBjava 8u111-jdk d23bdf5b1b1b 2 years ago 643MB
  • 此时,如果您的镜像列表出现<none>:<none>,您也能分析出此现象的来源了,接下来试试如何清理dangling images。

清理dangling images

  • 如下所示,执行命令docker image prune即可删除dangling images:
[email protected]:/home/willzhao/temp/201906/01/eureka-server# docker imagesREPOSITORY TAG IMAGE ID CREATED SIZEbolingcavalry/eureka-server 0.0.1-SNAPSHOT be262f101e2c About a minute ago 683MBbolingcavalry/eureka-server latest be262f101e2c About a minute ago 683MB<none> <none> 90b736eb388e 9 minutes ago 683MBjava 8u111-jdk d23bdf5b1b1b 2 years ago [email protected]:/home/willzhao/temp/201906/01/eureka-server# docker image pruneWARNING! This will remove all dangling images.Are you sure you want to continue? [y/N] yDeleted Images:deleted: sha256:90b736eb388e42df2e4bc2ab3c8770a9a5f7563bb5af2493b88428c610f14f6bdeleted: sha256:db3657b5e27b7bf6c780e3280d6f2e24ffc26592a14b4efa651000130294b429deleted: sha256:afd10ec003e3132ea5e1c489ba5e51f53b0759351bdc175184ba82daaac178d1Total reclaimed space: 39.94MB
  • 再次查看,发现90b736eb388e已经不在列表中:
[email protected]:/home/willzhao/temp/201906/01/eureka-server# docker imagesREPOSITORY TAG IMAGE ID CREATED SIZEbolingcavalry/eureka-server 0.0.1-SNAPSHOT be262f101e2c 39 minutes ago 683MBbolingcavalry/eureka-server latest be262f101e2c 39 minutes ago 683MBjava 8u111-jdk d23bdf5b1b1b 2 years ago 643MB

一点疑问

  • 再来看看官方对dangling images的解释,如下所示,有两个条件:没有标签、并且不再被容器使用:
    在这里插入图片描述

  • 我的疑问:如果没有标签,但是正在被容器使用的镜像,应该不算dangling images吧,此时如果执行命令docker image prune会怎么样呢?

  • 我的猜测:docker image prune是用来清理dangling images的,如果镜像正在被使用那就不算dangling images,那就不会被清理掉;

  • 还是动手来试试吧:

  • 执行以下命令会用镜像bolingcavalry/eureka-server:0.0.1-SNAPSHOT创建一个容器:

docker run -idt bolingcavalry/eureka-server:0.0.1-SNAPSHOT
  • 再次执行命令mvn clean package -U -DskipTests docker:build,也就是再构建一次;
  • 查看镜像信息如下,此时be262f101e2c在列表中已经显示成了<none>:<none>
[email protected]:/home/willzhao/temp/201906/01/eureka-server# docker imagesREPOSITORY TAG IMAGE ID CREATED SIZEbolingcavalry/eureka-server 0.0.1-SNAPSHOT f83762738051 4 seconds ago 683MBbolingcavalry/eureka-server latest f83762738051 4 seconds ago 683MB<none> <none> be262f101e2c About an hour ago 683MBjava 8u111-jdk d23bdf5b1b1b 2 years ago 643MB
  • 执行命令docker ps查看容器,发现IMAGE字段已经变成了ID(之前是bolingcavalry/eureka-server:0.0.1-SNAPSHOT):
[email protected]:/home/willzhao/temp/201906/01/eureka-server# docker psCONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMESf4e9b7aa6d25 be262f101e2c "java -jar /eureka-s…" 7 minutes ago Up 7 minutes gallant_bell
  • 执行命令docker image prune,再查看镜像列表,如下,可见be262f101e2c依旧在列表中,没有被清理掉,符合之前的猜测:被容器用到的镜像不是dangling images,用命令docker image prune无法清除:
[email protected]:/home/willzhao/temp/201906/01/eureka-server# docker image pruneWARNING! This will remove all dangling images.Are you sure you want to continue? [y/N] yTotal reclaimed space: [email protected]:/home/willzhao/temp/201906/01/eureka-server# docker imagesREPOSITORY TAG IMAGE ID CREATED SIZEbolingcavalry/eureka-server 0.0.1-SNAPSHOT f83762738051 5 minutes ago 683MBbolingcavalry/eureka-server latest f83762738051 5 minutes ago 683MB<none> <none> be262f101e2c About an hour ago 683MBjava 8u111-jdk d23bdf5b1b1b 2 years ago 643MB
  • 至此,对Docker镜像列表中的none:none已经了解,希望在您有类似疑惑时本文可以提供一些参考。

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