Docker 调试技巧

『重用』容器名

但我们在编写/调试Dockerfile的时候我们经常会重复之前的command,比如这种docker run --name jstorm-zookeeper zookeeper:3.4,然后就容器名就冲突了。

$ docker run --name jstorm-zookeeper zookeeper:3.4 ... $ docker run --name jstorm-zookeeper zookeeper:3.4 docker: Error response from daemon: Conflict. The name "/jstorm-zookeeper" is already in use by container xxxxxxxxx

可以在运行 docker run 时候加上--rm flag, 容器将在退出之后销毁。无需手动docker rm CONTAINER

$ docker run --name jstorm-zookeeper zookeeper:3.4 --rm  # reuse  $ docker create --name jstorm-zookeeper zookeeper:3.4 $ docker start jstorm-zookeeper  # no error

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debug Dockerfile

在写 Dockerfile 的时候,通常并不会一气呵成。有的时候容器启动就crash 直接退出,有的时候build image 就会失败,或者想验证Dockerfile是否符合预期,我们经常要debug Dockerfile。

如果build 失败可以直接 查看stdout的错误信息,拆分指令,重新build。

logs 查看 stdout

所有容器内写到stdout的内容都会被捕获到host中的一个history文件中, 可以通过 docker logs CONTAINER 查看。

$ docker run -d --name jstorm-zookeeper zookeeper:3.4  $ docker logs jstorm-zookeeper ZooKeeper JMX enabled by default Using config: /conf/zoo.cfg 2016-12-18 05:55:27,717 [myid:] - INFO  [main:QuorumPeerConfig@124] - Reading configuration from: /conf/zoo.cfg 2016-12-18 05:55:27,725 [myid:] - INFO  [main:DatadirCleanupManager@78] - autopurge.snapRetainCount set to 3 2016-12-18 05:55:27,725 [myid:] - INFO  [main:DatadirCleanupManager@79] - autopurge.purgeInterval set to 0 2016-12-18 05:55:27,726 [myid:] - INFO  [main:DatadirCleanupManager@101] - Purge task is not scheduled. 2016-12-18 05:55:27,728 [myid:] - WARN  [main:QuorumPeerMain@113] - Either no config or no quorum defined in config, running  in standalone mode 2016-12-18 05:55:27,746 [myid:] - INFO  [main:QuorumPeerConfig@124] - Reading configuration from: /conf/zoo.cfg 2016-12-18 05:55:27,747 [myid:] - INFO  [main:ZooKeeperServerMain@96] - Starting server 2016-12-18 05:55:27,766 [myid:] - INFO  [main:Environment@100] - Server environment:zookeeper.version=3.4.9-1757313, built on 08/23/2016 06:50 GMT 2016-12-18 05:55:27,766 [myid:] - INFO  [main:Environment@100] - Server environment:host.name=dbc742dd5688 2016-12-18 05:55:27,767 [myid:] - INFO  [main:Environment@100] - Server environment:java.version=1.8.0_111-internal

即使是容器已经退出的也可以看到,所以可以通过这种方式来分析非预期的退出。这些文件一直保存着,直到通过docker rm把容器删除。文件的具体路径可以通过docker inspect CONTAINER 获得。
(然后osx上你并找不到这些文件,因为其实osx的docker实际是运行在"VM"中,具体就不展开了,但是可以通过 screen ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/tty touch上"VM"的tty)

在使用docker logs 的时候加一些参数来过滤log,默认输出所有log。

Options:       --details        Show extra details provided to logs   -f, --follow         Follow log output       --help           Print usage       --since string   Show logs since timestamp       --tail string    Number of lines to show from the end of the logs (default "all")   -t, --timestamps     Show timestamps

attach 实时查看stdout

如果你想实时查看容器的输出你可以用 docker attach CONTAINER 命令。

默认会绑定stdin,代理signals, 所以如果你 ctrl-c 容器通常会退出。很多时候大家并不想这样,只是想分离开,可以ctrl-p ctrl-q

执行任意command

可以通过docker exec CONTAINER COMMAND,来在容器内执行任意 command,比如 cat 一些东西来debug。

$ docker run -d --name jstorm-zookeeper zookeeper:3.4  $ docker exec jstorm-zookeeper java -version openjdk version "1.8.0_111-internal" OpenJDK Runtime Environment (build 1.8.0_111-internal-alpine-r0-b14) OpenJDK 64-Bit Server VM (build 25.111-b14, mixed mode)

也可以直接通过 exec 在容器内启动一个 shell 更方便地调试容器,不必一条条执行docker exec

$ docker exec -it jstorm-zookeeper /bin/bash bash-4.3# pwd /zookeeper-3.4.9

docker exec 只能在正在运行的容器上使用,如果已经停止了退出了就不行了,就只好用 docker logs 了。

重写entrypointcmd

每个Docker镜像都有 entrypointcmd , 可以定义在 Dockerfile 中,也可以在运行时指定。这两个概念很容易混淆,而且它们的试用方式也不同。

entrypointcmd 更"高级",entrypoint 作为容器中pid为1的进程运行(docker不是虚拟机,只是隔离的进程。真正的linux中pid为1的是init)。
cmd 只是 entrypoint的参数:

<ENTRYPOINT> "<CMD>"

当我们没有指定 entrypoint 时缺省为 /bin/sh -c。所以其实 entrypoint 是真正表达这个docker应该干什么的,通常大家有一个shell 脚本来代理。
entrypointcmd 都可以在运行的时候更改,通过更改来看这样设置entrypoint是否优雅合理。

$ docker run -it --name jstorm-zookeeper --entrypoint /bin/bash zookeeper:3.4 bash-4.3# top Mem: 320212K used, 1725368K free, 89112K shrd, 35532K buff, 130532K cached CPU:   0% usr   0% sys   0% nic 100% idle   0% io   0% irq   0% sirq Load average: 0.20 0.06 0.02 5/195 7   PID  PPID USER     STAT   VSZ %VSZ CPU %CPU COMMAND     1     0 root     S     6220   0%   0   0% /bin/bash     7     1 root     R     1516   0%   2   0% top

任何 docker run 命令中在image名后的内容都作为cmd的内容传给 entrypoint当参数。

暂停容器

使用 docker pause 可以暂停容器中所有进程。这非常有用。

$ docker run -d --name jstorm-zookeeper zookeeper:3.4 && sleep 0.1 && docker pause jstorm-zookeeper && docker logs jstorm-zookeeper a24405a53ddd9b7d94d9e77fe2b5a67639a251d681aa2f34fcb0cc96f347ba48 jstorm-zookeeper ZooKeeper JMX enabled by default Using config: /conf/zoo.cfg 2016-12-18 16:17:47,720 [myid:] - INFO  [main:QuorumPeerConfig@124] - Reading configuration from: /conf/zoo.cfg 2016-12-18 16:17:47,730 [myid:] - INFO  [main:DatadirCleanupManager@78] - autopurge.snapRetainCount set to 3 2016-12-18 16:17:47,730 [myid:] - INFO  [main:DatadirCleanupManager@79] - autopurge.purgeInterval set to 0 2016-12-18 16:17:47,730 [myid:] - INFO  [main:DatadirCleanupManager@101] - Purge task is not scheduled. 2016-12-18 16:17:47,731 [myid:] - WARN  [main:QuorumPeerMain@113] - Either no config or no quorum defined in config, running  in standalone mode 2016-12-18 16:17:47,757 [myid:] - INFO  [main:QuorumPeerConfig@124] - Reading configuration from: /conf/zoo.cfg 2016-12-18 16:17:47,757 [myid:] - INFO  [main:ZooKeeperServerMain@96] - Starting server  $ docker unpause jstorm-zookeeper && docker logs jstorm-zookeeper jstorm-zookeeper ZooKeeper JMX enabled by default Using config: /conf/zoo.cfg 2016-12-18 16:17:47,720 [myid:] - INFO  [main:QuorumPeerConfig@124] - Reading configuration from: /conf/zoo.cfg 2016-12-18 16:17:47,730 [myid:] - INFO  [main:DatadirCleanupManager@78] - autopurge.snapRetainCount set to 3 2016-12-18 16:17:47,730 [myid:] - INFO  [main:DatadirCleanupManager@79] - autopurge.purgeInterval set to 0 2016-12-18 16:17:47,730 [myid:] - INFO  [main:DatadirCleanupManager@101] - Purge task is not scheduled. 2016-12-18 16:17:47,731 [myid:] - WARN  [main:QuorumPeerMain@113] - Either no config or no quorum defined in config, running  in standalone mode 2016-12-18 16:17:47,757 [myid:] - INFO  [main:QuorumPeerConfig@124] - Reading configuration from: /conf/zoo.cfg 2016-12-18 16:17:47,757 [myid:] - INFO  [main:ZooKeeperServerMain@96] - Starting server 2016-12-18 16:18:09,039 [myid:] - INFO  [main:Environment@100] - Server environment:zookeeper.version=3.4.9-1757313, built on 08/23/2016 06:50 GMT 2016-12-18 16:18:09,040 [myid:] - INFO  [main:Environment@100] - Server environment:host.name=a24405a53ddd 2016-12-18 16:18:09,040 [myid:] - INFO  [main:Environment@100] - Server environment:java.version=1.8.0_111-internal 2016-12-18 16:18:09,040 [myid:] - INFO  [main:Environment@100] - Server environment:java.vendor=Oracle Corporation 2016-12-18 16:18:09,040 [myid:] - INFO  [main:Environment@100] - Server environment:java.home=/usr/lib/jvm/java-1.8-openjdk/jre 2016-12-18 16:18:09,040 [myid:] - INFO  [main:Environment@100] - Server environment:java.class.path=/zookeeper-3.4.9/bin/../build/classes:/zookeeper-3.4.9/bin/../build/lib/*.jar:/zookeeper-3.4.9/bin/../lib/slf4j-log4j12-1.6.1.jar:/zookeeper-3.4.9/bin/../lib/slf4j-api-1.6.1.jar:/zookeeper-3.4.9/bin/../lib/netty-3.10.5.Final.jar:/zookeeper-3.4.9/bin/../lib/log4j-1.2.16.jar:/zookeeper-3.4.9/bin/../lib/jline-0.9.94.jar:/zookeeper-3.4.9/bin/../zookeeper-3.4.9.jar:/zookeeper-3.4.9/bin/../src/java/lib/*.jar:/conf: 2016-12-18 16:18:09,040 [myid:] - INFO  [main:Environment@100] - Server environment:java.library.path=/usr/lib/jvm/java-1.8-openjdk/jre/lib/amd64/server:/usr/lib/jvm/java-1.8-openjdk/jre/lib/amd64:/usr/lib/jvm/java-1.8-openjdk/jre/../lib/amd64:/usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib 2016-12-18 16:18:09,041 [myid:] - INFO  [main:Environment@100] - Server environment:java.io.tmpdir=/tmp 2016-12-18 16:18:09,041 [myid:] - INFO  [main:Environment@100] - Server environment:java.compiler=<NA> 2016-12-18 16:18:09,043 [myid:] - INFO  [main:Environment@100] - Server environment:os.name=Linux 2016-12-18 16:18:09,043 [myid:] - INFO  [main:Environment@100] - Server environment:os.arch=amd64 2016-12-18 16:18:09,044 [myid:] - INFO  [main:Environment@100] - Server environment:os.version=4.4.27-moby 2016-12-18 16:18:09,044 [myid:] - INFO  [main:Environment@100] - Server environment:user.name=zookeeper 2016-12-18 16:18:09,044 [myid:] - INFO  [main:Environment@100] - Server environment:user.home=/home/zookeeper 2016-12-18 16:18:09,044 [myid:] - INFO  [main:Environment@100] - Server environment:user.dir=/zookeeper-3.4.9 2016-12-18 16:18:09,057 [myid:] - INFO  [main:ZooKeeperServer@815] - tickTime set to 2000 2016-12-18 16:18:09,057 [myid:] - INFO  [main:ZooKeeperServer@824] - minSessionTimeout set to -1 2016-12-18 16:18:09,058 [myid:] - INFO  [main:ZooKeeperServer@833] - maxSessionTimeout set to -1 2016-12-18 16:18:09,076 [myid:] - INFO  [main:NIOServerCnxnFactory@89] - binding to port 0.0.0.0/0.0.0.0:2181

topstats 获得容器中进程的状态

docker top CONTAINER 和在容器里执行 top 的效果类似。

$ docker top jstorm-zookeeper PID    USER      TIME  COMMAND 24593  dockrema  0:01  /usr/lib/jvm/java-1.8-openjdk/jre/bin/java -Dzookeeper.log.dir=. .....  $ docker stats jstorm-zookeeper CONTAINER           CPU %     MEM USAGE / LIMIT       MEM %   NET I/O        BLOCK I/O   PIDS jstorm-zookeeper    0.00%     24.86 MiB / 1.951 GiB   1.24%   648 B / 648 B  0 B / 0 B   20

通过 inspect 查看容器的详细信息

docker inspect CONTAINER 饭后镜像和容器的详细信息。比如:

  • State —— 容器的当先状态

  • LogPath —— history(stdout) file 的路径

  • Config.Env —— 环境变量

  • NetworkSettings.Ports —— 端口的映射关系

环境变量非常有用很多问题都是环境变量引起的。

history 查看 image layers

可以看到各层创建的指令,大小和哈希。可以用来检查这个image是否符合你的预期。

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