提示:可以看到基于上面的dockerfile构建的镜像运行为容器,里面默认跑的进程就是我们在dockerfile中指定用户运行的进程;使用USER指定用户运行容器里的进程,需要注意该用户要对运行进程所需资源的所有权限;否则容器运行不起来;
2、HEALTHCHECK:该指令用于定义如何对容器做健康状态检测;运行为容器后,容器里的进程不挂掉,当然容器也就不会挂掉,但是存在一种情况,容器没有挂掉,容器里的进程无法正常提供服务了,这个时候我们就需要通过一定的手段,第一时间知道容器里的进程是否健康(是否能够正常提供服务);healthcheck指令就是用来定义如果去检测容器内部进程是否健康;语法格式HEALTHCHECK [OPTIONS] CMD command;其中CMD是固定格式,而后面的command是对容器里的进程做健康状态检查的命令;而options是用来指定对容器做健康状态检查的周期时间相关信息;--interval=DURATION (default: 30s),该选项用于指定对容器做健康状态检查的频率,默认是30s一次;--timeout=DURATION (default: 30s),该选项用于指定对容器内部的进程做健康状态检查的超时时长,默认是30秒;--start-period=DURATION (default: 0s)指定对容器中的进程做健康状态检查延迟时间,默认0表示不延迟;这里补充一点,之所以要延迟多少秒做健康状态检查是因为,docker运行为容器以后,会立刻把该容器的状态标记为running状态,而对于有些初始化比较慢的容器,如果马上对它做健康状态检查,可能是不健康的状态,这样一来我们对了解容器是否健康就不是很准确了;如果配合某些工具,很可能存在检测到容器不健康就把该容器删除,然后重新创建,以此重复;这样就会导致我们的容器启动不起来; --retries=N (default: 3)表示指定对容器做健康状态检查的重试次数,默认是3次;也就是说检查到容器不健康的前提或健康的前提,它都会检查3次,如果3次检查都是失败状态那么就标记该容器不健康;而对于我们指定的命令来讲,命令的返回值就决定了容器是否健康,通常命令返回值为0表示我们执行的命令正常退出,也就意味着容器是健康状态;命令返回值为1表示容器不健康;返回值为2我们通常都是保留不使用;HEALTHCHECK NONE就表示不对容器做健康状态检查;
示例:
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[root@node1 test ] # cat Dockerfile FROM centos:7 LABEL maintainer= "qiuhom <qiuhom@linux-1874.com>" LABEL version= "1.0" LABEL description= "this is test file \ that label-values can span multiple lines." RUN yum install -y httpd ADD ok.html /var/www/html/ CMD [ "/usr/sbin/httpd" , "-DFOREGROUND" ] HEALTHCHECK --interval=5s --timeout=5s --start-period=5s --retries=2 \ CMD curl -f http: //localhost/ok .html || exit 1 [root@node1 test ] # |
提示:以上HEALTHCHECK指令表示每5秒检查一次,超时时长为5秒,延迟5秒开始检查,重试2次;如果curl -f http://localhost/ok.html这条命令正常返回0,那么就表示容器健康,否则就返回1,表示容器不健康;
验证:把以上dockerfile构建成镜像启动为容器,我们把ok.html删除或移动到别的目录,看看容器是否标记为不健康?
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[root@node1 test ] # docker build . -t test:v1.1 Sending build context to Docker daemon 1.052MB Step 1 /8 : FROM centos:7 ---> b5b4d78bc90c Step 2 /8 : LABEL maintainer= "qiuhom <qiuhom@linux-1874.com>" ---> Using cache ---> d31363b96f38 Step 3 /8 : LABEL version= "1.0" ---> Using cache ---> 2281f36d7c3c Step 4 /8 : LABEL description= "this is test file \ that label-values can span multiple lines." ---> Using cache ---> 8de872e222fb Step 5 /8 : RUN yum install -y httpd ---> Running in 9964718a2c3e Loaded plugins: fastestmirror, ovl Determining fastest mirrors * base: mirrors.bfsu.edu.cn * extras: mirrors.aliyun.com * updates: mirrors.aliyun.com Resolving Dependencies --> Running transaction check ---> Package httpd.x86_64 0:2.4.6-93.el7.centos will be installed --> Processing Dependency: httpd-tools = 2.4.6-93.el7.centos for package: httpd-2.4.6-93.el7.centos.x86_64 --> Processing Dependency: system-logos >= 7.92.1-1 for package: httpd-2.4.6-93.el7.centos.x86_64 --> Processing Dependency: /etc/mime .types for package: httpd-2.4.6-93.el7.centos.x86_64 --> Processing Dependency: libaprutil-1.so.0()(64bit) for package: httpd-2.4.6-93.el7.centos.x86_64 --> Processing Dependency: libapr-1.so.0()(64bit) for package: httpd-2.4.6-93.el7.centos.x86_64 --> Running transaction check ---> Package apr.x86_64 0:1.4.8-5.el7 will be installed ---> Package apr-util.x86_64 0:1.5.2-6.el7 will be installed ---> Package centos-logos.noarch 0:70.0.6-3.el7.centos will be installed ---> Package httpd-tools.x86_64 0:2.4.6-93.el7.centos will be installed ---> Package mailcap.noarch 0:2.1.41-2.el7 will be installed --> Finished Dependency Resolution Dependencies Resolved ================================================================================ Package Arch Version Repository Size ================================================================================ Installing: httpd x86_64 2.4.6-93.el7.centos base 2.7 M Installing for dependencies: apr x86_64 1.4.8-5.el7 base 103 k apr-util x86_64 1.5.2-6.el7 base 92 k centos-logos noarch 70.0.6-3.el7.centos base 21 M httpd-tools x86_64 2.4.6-93.el7.centos base 92 k mailcap noarch 2.1.41-2.el7 base 31 k Transaction Summary ================================================================================ Install 1 Package (+5 Dependent packages) Total download size: 24 M Installed size: 32 M Downloading packages: warning: /var/cache/yum/x86_64/7/base/packages/apr-1 .4.8-5.el7.x86_64.rpm: Header V3 RSA /SHA256 Signature, key ID f4a80eb5: NOKEY Public key for apr-1.4.8-5.el7.x86_64.rpm is not installed -------------------------------------------------------------------------------- Total 2.0 MB /s | 24 MB 00:12 Retrieving key from file : ///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7 Importing GPG key 0xF4A80EB5: Userid : "CentOS-7 Key (CentOS 7 Official Signing Key) <security@centos.org>" Fingerprint: 6341 ab27 53d7 8a78 a7c2 7bb1 24c6 a8a7 f4a8 0eb5 Package : centos-release-7-8.2003.0.el7.centos.x86_64 (@CentOS) From : /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7 Running transaction check Running transaction test Transaction test succeeded Running transaction Installing : apr-1.4.8-5.el7.x86_64 1 /6 Installing : apr-util-1.5.2-6.el7.x86_64 2 /6 Installing : httpd-tools-2.4.6-93.el7.centos.x86_64 3 /6 Installing : centos-logos-70.0.6-3.el7.centos.noarch 4 /6 Installing : mailcap-2.1.41-2.el7.noarch 5 /6 Installing : httpd-2.4.6-93.el7.centos.x86_64 6 /6 Verifying : mailcap-2.1.41-2.el7.noarch 1 /6 Verifying : apr-util-1.5.2-6.el7.x86_64 2 /6 Verifying : httpd-2.4.6-93.el7.centos.x86_64 3 /6 Verifying : apr-1.4.8-5.el7.x86_64 4 /6 Verifying : httpd-tools-2.4.6-93.el7.centos.x86_64 5 /6 Verifying : centos-logos-70.0.6-3.el7.centos.noarch 6 /6 Installed: httpd.x86_64 0:2.4.6-93.el7.centos Dependency Installed: apr.x86_64 0:1.4.8-5.el7 apr-util.x86_64 0:1.5.2-6.el7 centos-logos.noarch 0:70.0.6-3.el7.centos httpd-tools.x86_64 0:2.4.6-93.el7.centos mailcap.noarch 0:2.1.41-2.el7 Complete! Removing intermediate container 9964718a2c3e ---> a931e93eea06 Step 6 /8 : ADD ok.html /var/www/html/ ---> 97e61f41911d Step 7 /8 : CMD [ "/usr/sbin/httpd" , "-DFOREGROUND" ] ---> Running in e91ccdef90c2 Removing intermediate container e91ccdef90c2 ---> 7c8af9bb7eb3 Step 8 /8 : HEALTHCHECK --interval=5s --timeout=5s --start-period=5s --retries=2 CMD curl -f http: //localhost/ok .html || exit 1 ---> Running in 80682ab087d3 Removing intermediate container 80682ab087d3 ---> aa53cba15046 Successfully built aa53cba15046 Successfully tagged test :v1.1 [root@node1 test ] # docker images REPOSITORY TAG IMAGE ID CREATED SIZE test v1.1 aa53cba15046 8 seconds ago 312MB test v1 461f6ceabc88 57 minutes ago 204MB centos 7 b5b4d78bc90c 4 weeks ago 203MB [root@node1 test ] # docker run --name t1 --rm -d test:v1.1 332590e683fcb29f60a28703548fce7aa83df715cbb840e1283472834867d6a1 [root@node1 test ] # docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 332590e683fc test :v1.1 "/usr/sbin/httpd -DF…" 3 seconds ago Up 2 seconds (health: starting) t1 [root@node1 test ] # docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 332590e683fc test :v1.1 "/usr/sbin/httpd -DF…" 7 seconds ago Up 6 seconds (healthy) t1 [root@node1 test ] # |