“什么是Docker“？，”为什么要使用Docker”？
官方定义：
Docker是一个开源的应用容器引擎，让开发者可以打包他们的应用及依赖到一个可移植的容器中，然后发布到任何流行的Linux机器或Windows机器上，也可以实现虚拟化，容器是完全使用沙箱机制，相互之间不会有任何接口；
通俗解释：
一款产品从开发到上线，到操作系统，到运行环境，再到应用配置，我们需要关注很多东西，这是大多数互联网不得不面对的问题，特别是版本的迭代，不同版本环境的兼容等等；Docker给出了一个标准化的解决方案，“从搬家，到搬楼”，即之前我们配置一个应用的运行环境，要安装很多软件，如：Java/Tomcat/Mysql/Jdbc驱动等等，安装配置麻烦，而且不能跨平台，换个服务器还要重新配置以便，移植性差，而Docker做到了“一次构建，处处运行”，将这些配置完的软件生成镜像，在别的服务器上直接调用即可，不需要重新去配置；
Docker核心概念：
docker主机（Host）：安装了docker程序的机器（docker直接安装在操作系统之上的）；
docker客户端（Client）：连接docker主机进行操作的程序；
docker仓库（Registry）：用来保存各种打包好的软件镜像；
docker镜像（Images）：软件打包好的镜像，放在docker仓库中；
docker容器（Container）：镜像启动后的实例称为一个容器；容器是一个独立运行的一个或一组应用；
Docker安装：
在Linux操作系统上安装docker，本人是通过虚拟机来完成的，涉及到的虚拟机的安装，本文中不做说明。
1.检查Linux内核版本（docker安装要求内核版本是3.10及以上）
[root@localhost /]# uname -r
3.10.0-1160.el7.x86_64
[root@localhost /]# 2.安装docker（CentOS7和CentOS8安装的结果好像是不一样的，此处以CentOS7来说明）
yum install docker3.安装完成之后，可通过下面命令来操作
#启动docker
[root@localhost /]# systemctl start docker
#查看docker版本
[root@localhost /]# docker -v
Docker version 1.13.1, build 7d71120/1.13.1
#查看docker状态
[root@localhost /]# systemctl status docker
● docker.service - Docker Application Container Engine
Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
Active: active (running) since 二 2021-10-19 18:01:03 CST; 20s ago
Docs: http://docs.docker.com
Main PID: 4984 (dockerd-current)
Tasks: 17
Memory: 22.5M
CGroup: /system.slice/docker.service
├─4984 /usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current --default-runtime=docker-runc --exec-opt native.cgroupdriver...
└─4989 /usr/bin/docker-containerd-current -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeout 2m --state-dir /...
10月 19 18:01:01 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:01.764522960+08:00" level=info msg="libcontainerd: new containerd process, pid: 4989"
10月 19 18:01:03 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:03.169740757+08:00" level=info msg="Graph migration to content-addressabili...seconds"
10月 19 18:01:03 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:03.171913151+08:00" level=info msg="Loading containers: start."
10月 19 18:01:03 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:03.187520490+08:00" level=info msg="Firewalld running: false"
10月 19 18:01:03 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:03.363977682+08:00" level=info msg="Default bridge (docker0) is assigned wi...address"
10月 19 18:01:03 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:03.765296618+08:00" level=info msg="Loading containers: done."
10月 19 18:01:03 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:03.862231739+08:00" level=info msg="Daemon has completed initialization"
10月 19 18:01:03 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:03.862256098+08:00" level=info msg="Docker daemon" commit="7d71120/1.13.1" ...n=1.13.1
10月 19 18:01:03 localhost.localdomain dockerd-current[4984]: time="2021-10-19T18:01:03.882963717+08:00" level=info msg="API listen on /var/run/docker.sock"
10月 19 18:01:03 localhost.localdomain systemd[1]: Started Docker Application Container Engine.
Hint: Some lines were ellipsized, use -l to show in full.
#停止docker
[root@localhost /]# systemctl stop docker
[root@localhost /]#Docker常用的操作命令
1）、镜像操作命令
①检索镜像文件命令：docker search 关键字
[root@localhost /]# docker search tomcat
INDEX NAME DESCRIPTION STARS OFFICIAL AUTOMATED
docker.io docker.io/tomcat Apache Tomcat is an open source implementa... 3152 [OK]
docker.io docker.io/tomee Apache TomEE is an all-Apache Java EE cert... 93 [OK]
docker.io docker.io/dordoka/tomcat Ubuntu 14.04, Oracle JDK 8 and Tomcat 8 ba... 58 [OK]
docker.io docker.io/consol/tomcat-7.0 Tomcat 7.0.57, 8080, "admin/admin" 18 [OK]
docker.io docker.io/cloudesire/tomcat Tomcat server, 6/7/8 15 [OK]
docker.io docker.io/aallam/tomcat-mysql Debian, Oracle JDK, Tomcat & MySQL 13 [OK]
docker.io docker.io/arm32v7/tomcat Apache Tomcat is an open source implementa... 11
docker.io docker.io/andreptb/tomcat Debian Jessie based image with Apache Tomc... 10 [OK]
docker.io docker.io/rightctrl/tomcat CentOS , Oracle Java, tomcat application s... 7 [OK]
docker.io docker.io/arm64v8/tomcat Apache Tomcat is an open source implementa... 6
docker.io docker.io/unidata/tomcat-docker Security-hardened Tomcat Docker container. 5 [OK]
docker.io docker.io/amd64/tomcat Apache Tomcat is an open source implementa... 3
docker.io docker.io/cfje/tomcat-resource Tomcat Concourse Resource 2
docker.io docker.io/fabric8/tomcat-8 Fabric8 Tomcat 8 Image 2 [OK]
docker.io docker.io/jelastic/tomcat An image of the Tomcat Java application se... 2
docker.io docker.io/oobsri/tomcat8 Testing CI Jobs with different names. 2
docker.io docker.io/99taxis/tomcat7 Tomcat7 1 [OK]
docker.io docker.io/camptocamp/tomcat-logback Docker image for tomcat with logback integ... 1 [OK]
docker.io docker.io/chenyufeng/tomcat-centos tomcat基于centos6的镜像 1 [OK]
docker.io docker.io/i386/tomcat Apache Tomcat is an open source implementa... 1
docker.io docker.io/picoded/tomcat7 tomcat7 with jre8 and MANAGER_USER / MANAG... 1 [OK]
docker.io docker.io/ppc64le/tomcat Apache Tomcat is an open source implementa... 1
docker.io docker.io/s390x/tomcat Apache Tomcat is an open source implementa... 0
docker.io docker.io/secoresearch/tomcat-varnish Tomcat and Varnish 5.0 0 [OK]
docker.io docker.io/softwareplant/tomcat Tomcat images for jira-cloud testing 0 [OK]
[root@localhost /]# ②拉取镜像命令：docker pull 镜像名:tag
[root@localhost /]# docker pull tomcat
Using default tag: latest #默认不写tag标签时，拉取的就是最新版
Trying to pull repository docker.io/library/tomcat ...
latest: Pulling from docker.io/library/tomcat
bb7d5a84853b: Pull complete
f02b617c6a8c: Pull complete
d32e17419b7e: Pull complete
c9d2d81226a4: Pull complete
fab4960f9cd2: Pull complete
da1c1e7baf6d: Pull complete
79b231561270: Pull complete
7d337880d8b4: Pull complete
2df65a31be06: Pull complete
10cbf519de23: Pull complete
Digest: sha256:7c30d3c92b191ec2b84f64be99326f9c83a4a4e079c899ee4d0a9a41abca8406
Status: Downloaded newer image for docker.io/tomcat:latest
[root@localhost /]# ③查看下载的所有镜像文件：docker images
[root@localhost /]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
docker.io/mysql latest ecac195d15af 12 hours ago 516 MB
docker.io/tomcat latest 4ce9babdd885 5 days ago 680 MB
[root@localhost /]# ④删除下载的镜像文件：docker rmi 镜像名/镜像ID
[root@localhost /]# docker rmi redis
Untagged: redis:latest
Untagged: docker.io/redis@sha256:a89cb097693dd354de598d279c304a1c73ee550fbfff6d9ee515568e0c749cfe
Deleted: sha256:7faaec68323851b2265bddb239bd9476c7d4e4335e9fd88cbfcc1df374dded2f
Deleted: sha256:e6deb90762475cda72e21895911f830ed99fd1cc6d920d92873270be91235274
Deleted: sha256:2649acad13241d9c8d81e49357bc66cce459b352ded7f423d70ede7bd3bb7b89
Deleted: sha256:64007bba5fc220df4d3da33cecdc2d55dd6a73528c138b0fa1acd79fd6a9c217
Deleted: sha256:b2cc2f1bf8b1cca8ba7c19e1697f7b73755903ad8f880b83673fd6a697aca935
Deleted: sha256:fbd1283ab782925be4d990bd4bebe9ad5e5cf9a525abfb6fa87465e072da9d31
Deleted: sha256:e8b689711f21f9301c40bf2131ce1a1905c3aa09def1de5ec43cf0adf652576e
[root@localhost /]# 2）、容器操作命令
①根据镜像启动容器： docker run
[root@localhost /]# docker run --name tomcat -d -p 8888:8080 tomcat
2a52a81aa35b0a030096a9ea8b81c91ef7edb8f931f2654581c5c9655f544734
[root@localhost /]#
●--name 容器自定义名称
● -d 后台运行
● -p 端口映射
注意：容器创建之后可以停止运行的容器，但是下次启动的时候可以通过start来启动，除非容器删除了才通过run来启动②查看容器命令： docker ps
#查看运行中的容器
[root@localhost /]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
2a52a81aa35b tomcat "catalina.sh run" 8 minutes ago Up 8 minutes 0.0.0.0:8888->8080/tcp tomcat
#查看所有的容器（包括运行中的和已经停止的）
[root@localhost /]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
2a52a81aa35b tomcat "catalina.sh run" 8 minutes ago Up 8 minutes 0.0.0.0:8888->8080/tcp tomcat
[root@localhost /]# ③停止运行中的容器：docker stop 容器名/容器ID
[root@localhost /]# docker stop tomcat
tomcat
[root@localhost /]# ④删除容器： docker rm 容器名/容器ID
[root@localhost /]# docker rm tomcat
tomcat
[root@localhost /]# ⑤查看容器日志：docker logs 容器名/容器ID
[root@localhost /]# docker logs tomcat
NOTE: Picked up JDK_JAVA_OPTIONS: --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.io=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.base/java.util.concurrent=ALL-UNNAMED --add-opens=java.rmi/sun.rmi.transport=ALL-UNNAMED
19-Oct-2021 10:29:37.143 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Server version name: Apache Tomcat/10.0.12
19-Oct-2021 10:29:37.146 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Server built: Sep 28 2021 13:34:21 UTC
19-Oct-2021 10:29:37.162 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Server version number: 10.0.12.0
19-Oct-2021 10:29:37.162 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log OS Name: Linux
19-Oct-2021 10:29:37.168 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log OS Version: 3.10.0-1160.el7.x86_64
19-Oct-2021 10:29:37.168 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Architecture: amd64
19-Oct-2021 10:29:37.169 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Java Home: /usr/local/openjdk-11
19-Oct-2021 10:29:37.169 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log JVM Version: 11.0.12+7
19-Oct-2021 10:29:37.169 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log JVM Vendor: Oracle Corporation
19-Oct-2021 10:29:37.169 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log CATALINA_BASE: /usr/local/tomcat
19-Oct-2021 10:29:37.169 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log CATALINA_HOME: /usr/local/tomcat
19-Oct-2021 10:29:37.200 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: --add-opens=java.base/java.lang=ALL-UNNAMED
19-Oct-2021 10:29:37.200 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: --add-opens=java.base/java.io=ALL-UNNAMED
19-Oct-2021 10:29:37.201 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: --add-opens=java.base/java.util=ALL-UNNAMED
19-Oct-2021 10:29:37.201 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: --add-opens=java.base/java.util.concurrent=ALL-UNNAMED
19-Oct-2021 10:29:37.202 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: --add-opens=java.rmi/sun.rmi.transport=ALL-UNNAMED
19-Oct-2021 10:29:37.202 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.util.logging.config.file=/usr/local/tomcat/conf/logging.properties
19-Oct-2021 10:29:37.202 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager
19-Oct-2021 10:29:37.202 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djdk.tls.ephemeralDHKeySize=2048
19-Oct-2021 10:29:37.202 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.protocol.handler.pkgs=org.apache.catalina.webresources
19-Oct-2021 10:29:37.202 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Dorg.apache.catalina.security.SecurityListener.UMASK=0027
19-Oct-2021 10:29:37.203 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Dignore.endorsed.dirs=
19-Oct-2021 10:29:37.203 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Dcatalina.base=/usr/local/tomcat
19-Oct-2021 10:29:37.203 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Dcatalina.home=/usr/local/tomcat
19-Oct-2021 10:29:37.204 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.io.tmpdir=/usr/local/tomcat/temp
19-Oct-2021 10:29:37.222 INFO [main] org.apache.catalina.core.AprLifecycleListener.lifecycleEvent Loaded Apache Tomcat Native library [1.2.31] using APR version [1.7.0].
19-Oct-2021 10:29:37.222 INFO [main] org.apache.catalina.core.AprLifecycleListener.lifecycleEvent APR capabilities: IPv6 [true], sendfile [true], accept filters [false], random [true], UDS [true].
19-Oct-2021 10:29:37.231 INFO [main] org.apache.catalina.core.AprLifecycleListener.initializeSSL OpenSSL successfully initialized [OpenSSL 1.1.1k 25 Mar 2021]
19-Oct-2021 10:29:38.652 INFO [main] org.apache.coyote.AbstractProtocol.init Initializing ProtocolHandler ["http-nio-8080"]
19-Oct-2021 10:29:38.749 INFO [main] org.apache.catalina.startup.Catalina.load Server initialization in [2379] milliseconds
19-Oct-2021 10:29:38.963 INFO [main] org.apache.catalina.core.StandardService.startInternal Starting service [Catalina]
19-Oct-2021 10:29:38.963 INFO [main] org.apache.catalina.core.StandardEngine.startInternal Starting Servlet engine: [Apache Tomcat/10.0.12]
19-Oct-2021 10:29:38.999 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["http-nio-8080"]
19-Oct-2021 10:29:39.037 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in [288] milliseconds
[root@localhost /]#