为什么在docker-compose.yml中需要tty：true而其他图像不需要？

Question

我一直在寻找答案，但我没有找到它，我需要在我继续我的测试之前弄明白。

我正在通过安装bash创建一个基于Alpine的映像，如下图所示：

FROM alpine:3.12

RUN apk add --no-cache --upgrade bash rsync gzip \
&& rm -rf /var/cache/apk/*

COPY ./docker/backup/hello.sh /hello.sh

RUN mkdir /backup \
&& chmod u+x /hello.sh

WORKDIR /backup

ENTRYPOINT ["sh","/hello.sh"]
CMD ["/bin/bash"]

Hello.sh

#!/bin/sh
echo "=> Hello Word"
echo "$@"
exec "$@"

docker-compose exec myalpine bash

services:
  myalpine:
    build:
      context: ./
      dockerfile: ./docker/backup/Dockerfile
      args:
        - DOCKER_ENV=${DOCKER_ENV}
    restart: unless-stopped
    tty: true
    container_name: ${PROJECT_NAME}-files
    volumes:
      - appdata:/app
      - ./data/app/backup:/backup
  mysql:
    build:
      context: ./
      dockerfile: ./docker/mysql/Dockerfile
      args:
        - MYSQL_VERSION=${MYSQL_VERSION}
        - DOCKER_ENV=${DOCKER_ENV}
    restart: always
    container_name: ${PROJECT_NAME}-mysql
    environment:
      MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
      MYSQL_DATABASE: ${MYSQL_DATABASE}
      MYSQL_USER: ${MYSQL_USER}
      MYSQL_PASSWORD: ${MYSQL_PASSWORD}
    volumes:
      - dbdata:/var/lib/mysql
    networks:
      - db

docker-compose exec mysql bash

我可以在不向docker-compose.yml添加tty:true的情况下访问，所以Alpine的映像中一定有我不理解和希望理解的东西。

Answer 1

我用dockerfile和docker-compose.yaml的精简版本复制了您的示例，然后运行docker-compose up。首先，我在没有附加TTY的情况下运行，因此有以下内容：

~$ docker-compose up
...
...
WARNING: Image for service myalpine was built because it did not already exist. To rebuild this image you must use `docker-compose build` or `docker-compose up --build`.
Creating test-fies ... done
Attaching to test-fies
test-fies   | => Hello Word
test-fies   | /bin/bash

~# docker ps
CONTAINER ID   IMAGE             COMMAND                  CREATED         STATUS                                  PORTS                                              NAMES
9a72817b0e28   tty_up_myalpine   "sh /hello.sh /bin/b…"   5 minutes ago   Restarting (0) Less than a second ago                                                      myalpine-fies

如您所见，容器一直在重新启动。原因是hello.sh作为入口点将接收命令/bin/bash并执行bash。这将尝试创建交互式shell，但是由于没有TTY，因此shell的创建失败，容器停止。因为容器标记为restart:除非-stopped，所以它将处于一个不断的重新启动循环中。

由于容器未运行，您无法执行docker-compose exec myalpine bash

CONTAINER ID   IMAGE             COMMAND                  CREATED          STATUS         PORTS                                              NAMES
745f5139f510   tty_up_myalpine   "sh /hello.sh /bin/b…"   10 seconds ago   Up 9 seconds                                                      myalpine-fies