# ENTRYPOINT **ENTRYPOINT有两种形式：** **exec形式（我们优先选择的形式）** ``` ENTRYPOINT ["executable", "param1", "param2"] ``` **shell形式** ``` ENTRYPOINT command param1 param2 ``` **ENTRYPOINT**允许我们配置容器并作为可执行文件运行。 例如，以下代码以其默认内容启动**nginx**，监听端口**80**： ``` $ docker run -i -t --rm -p 80:80 nginx ``` **docker run**的命令行参数将添加到**exec**形式的**ENTRYPOINT**的所有元素之后，并覆盖使用**CMD**指定的所有元素。这允许我们将参数传递给**入口（entry point）**，即**docker run -d**将**-d**参数传递给**入口（entry point）**。我们可以使用**docker run --entrypoint**覆盖**ENTRYPOINT指令**。 Demon1: **main.go:** ```go package main import ( "flag" "fmt" ) type Usage struct { Name string Age string Address string Sex string } const ( name = ` The name flag is used to set a new name. The default value is TonyYang. ` age = ` The age flag is used to set a new age. The default value is 31. ` address = ` The address flag is used to set a new address. The default value is ChangZhou. ` sex = ` The sex flag is used to set a new sex. The default value is TonyYang. ` ) var usage = Usage{ Name: name, Age: age, Address: address, Sex: sex, } func main() { var ( fName = flag.String("name", "TonyYang", usage.Name) fAge = flag.String("age", "31", usage.Age) fAddress = flag.String("address", "ChangZhou", usage.Address) fSex = flag.String("sex", "male", usage.Sex) ) flag.Parse() infos := map[string]*string{ "name": fName, "age": fAge, "address": fAddress, "sex": fSex, } for k, v := range infos { fmt.Printf("The %s is %s\n", k, *v) } } ``` **Dockerfile:** ``` FROM golang:1.16 AS go WORKDIR /my_executable/ COPY . . RUN go build main.go && rm main.go FROM alpine:latest WORKDIR /tmp/executable/ COPY --from=go /my_executable/main . ENTRYPOINT ["./main"] CMD ["--name=Mae", "--age=30", "--address=ShangHai", "--sex=female"] ``` 上面定义了一个测试**ENTRYPOINT**的**Dockerfile**，通过**go语言**编写。 ```bash $ docker run camelgem/entrypoint_demo:v1 ``` 默认不为**run**指定运行的参数，输出结果如下所示： ``` The name is Mae The age is 30 The address is ShangHai The sex is female ``` 输出的结果符合我们**CMD**中设置的参数默认值。 ```bash $ docker run camelgem/entrypoint_demo:v1 --name="camelgem" ``` ``` The address is ChangZhou The sex is male The name is CamelGem The age is 31 ``` 当为**run**指定参数以后，输出结果发生了改变，输出的值不再按照**CMD**中设定的那样。在这里**name**变成了**CamelGem**，而其余的值是我在程序中设置的默认值。由此可以看出，一旦为**run**指定了参数，**CMD**中的值就会被全部覆盖掉。 **Shell**形式可防止使用任何**CMD**或**run**命令行指定的参数，但具有以下缺点：**ENTRYPOINT**将作为**/bin/sh -c**的子命令启动，该子命令不传递信号。这意味着可执行文件进程将不是容器的**PID 1**，并且不会接收**Unix**信号，因此可执行文件将不会从**docker stop** 接收到**SIGTERM**。 **只有Dockerfile中的最后一条ENTRYPOINT指令才会生效。** 我们可以使用**ENTRYPOINT**的**exec**形式来设置相当稳定的默认命令和参数，然后使用**CMD**来设置更有可能被更改的其他的默认值。 ``` FROM ubuntu ENTRYPOINT ["top", "-b"] CMD ["-c"] ``` 当运行容器时，可以看到**top**是唯一的进程： ```bash $ docker run -it --rm --name test top -H top - 08:25:00 up 7:27, 0 users, load average: 0.00, 0.01, 0.05 Threads: 1 total, 1 running, 0 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.1 us, 0.1 sy, 0.0 ni, 99.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st KiB Mem: 2056668 total, 1616832 used, 439836 free, 99352 buffers KiB Swap: 1441840 total, 0 used, 1441840 free. 1324440 cached Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1 root 20 0 19744 2336 2080 R 0.0 0.1 0:00.04 top ``` 要进一步检查结果，可以使用**docker exec**: ```bash $ docker exec -it test ps aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 2.6 0.1 19752 2352 ? Ss+ 08:24 0:00 top -b -H root 7 0.0 0.1 15572 2164 ? R+ 08:25 0:00 ps aux ``` 我们可以使用**docker stop test**优雅地请求**top**关闭。 以下的示例，我们使用**ENTRYPOINT**来使用**Apache**服务器运行在前台： ``` FROM debian:stable RUN apt-get update && apt-get install -y --force-yes apache2 EXPOSE 80 443 VOLUME ["/var/www", "/var/log/apache2", "/etc/apache2"] ENTRYPOINT ["/usr/sbin/apache2ctl", "-D", "FOREGROUND"] ``` 如果我们需要为单个可执行文件编写启动脚本，则可以使用**exec**和**gosu**命令确保最终可执行程序能够接收到**Unix**信号： ```bash #!/usr/bin/env bash set -e if [ "$1" = 'postgres' ]; then chown -R postgres "$PGDATA" if [ -z "$(ls -A "$PGDATA")" ]; then gosu postgres initdb fi exec gosu postgres "$@" fi exec "$@" ``` 最后，如果我们需要在关闭进程时进行一些额外的清理（或与其他容器通信），或正在协调多个可执行的容器，我们需要确保**ENTRYPOINT**脚本接收到**Unix**信号，传递它们，然后执行更多工作： ```bash #!/bin/sh # Note: I've written this using sh so it works in the busybox container too # USE the trap if you need to also do manual cleanup after the service is stopped, # or need to start multiple services in the one container trap "echo TRAPed signal" HUP INT QUIT TERM # start service in background here /usr/sbin/apachectl start echo "[hit enter key to exit] or run 'docker stop '" read # stop service and clean up here echo "stopping apache" /usr/sbin/apachectl stop echo "exited $0" ``` 如果我们通过**docker run -it --rm -p 80:80 --name test apache**，我们可以通过**docker exec**或**docker top**来查看容器的进程，然后让脚本停止**Apache**进程。 ```bash $ docker exec -it test ps aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.1 0.0 4448 692 ? Ss+ 00:42 0:00 /bin/sh /run.sh 123 cmd cmd2 root 19 0.0 0.2 71304 4440 ? Ss 00:42 0:00 /usr/sbin/apache2 -k start www-data 20 0.2 0.2 360468 6004 ? Sl 00:42 0:00 /usr/sbin/apache2 -k start www-data 21 0.2 0.2 360468 6000 ? Sl 00:42 0:00 /usr/sbin/apache2 -k start root 81 0.0 0.1 15572 2140 ? R+ 00:44 0:00 ps aux $ docker top test PID USER COMMAND 10035 root {run.sh} /bin/sh /run.sh 123 cmd cmd2 10054 root /usr/sbin/apache2 -k start 10055 33 /usr/sbin/apache2 -k start 10056 33 /usr/sbin/apache2 -k start $ /usr/bin/time docker stop test test real 0m 0.27s user 0m 0.03s sys 0m 0.03s ``` **NOTE:** 我们可以通过使用**--entrypoint**来覆盖**ENTRYPOINT**的设置，但是这只能设置二进制的可执行程序（不会使用**sh -c**）。 **exec**形式会被解析为**JSON数组**，这意味着我们必须使用**双引号**来包围单词，而不是通过**单引号**。 与**shell**形式不同，**exec**形式不会调用一个命令行**shell**。这意味着不会发生正常的**shell**处理。例如，**ENTRYPOINT \["echo", "$HOME"]**将不会进行变量替换。如果你希望发生**shell**处理，那么既可以使用**shell**形式也可以直接执行一个**shell**，例如：**ENTRYPOINT \["sh", "-c", "echo $HOME"]**。当使用**exec**形式并且直接执行一个**shell**，这种情况下，对环境变量进行扩展的是**shell**而不是**docker**。 ### --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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