如何修复使用Cron作为非root用户将文件写入可访问卷的Alpine镜像权限问题

Question

我正在尝试在Docker中创建一个多阶段构建，它简单地运行一个非root的crontab，并将写入可从容器外部访问的卷。我遇到了两个问题：权限、卷的外部访问和cron：

1. dockerfile中的第一个构建使用entry-point和su-exec创建了一个非root用户镜像，有助于通过volume解决权限问题！
2. 在同一dockerfile中的第二个构建使用第一个镜像来运行crond进程，通常会写入/backup文件夹。

用于构建dockerfile的docker-compose.yml文件：

version: '3.4'
services:
  scrap_service:
        build: .
        container_name: "flight_scrap"
        volumes:
          - /home/rey/Volumes/mongo/backup:/backup

在 DockerFile 的第一步骤中 (1)，我尝试将 Denis Bertovic 给出的答案应用于 Alpine 镜像。 （链接）

############################################################
# STAGE 1
############################################################

# Create first stage image
FROM gliderlabs/alpine:edge as baseStage

RUN echo http://nl.alpinelinux.org/alpine/edge/testing >> /etc/apk/repositories
RUN apk add --update && apk add -f gnupg ca-certificates curl dpkg su-exec shadow

COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh

# ADD NON ROOT USER, i hard fix value to 1000, my current id 
RUN addgroup scrapy \
    && adduser -h /home/scrapy -u 1000 -S -G scrapy scrapy

ENTRYPOINT ["/usr/local/bin/docker-entrypoint.sh"]

我用于修复权限的docker-entrypoint.sh脚本如下:

#!/usr/bin/env bash
chown -R scrapy .
exec su-exec scrapy "$@"

第二阶段（2）运行cron服务，将数据写入已挂载为卷的/backup文件夹。

############################################################
# STAGE 2
############################################################

FROM baseStage
MAINTAINER rey 

ENV TZ=UTC
RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone

RUN apk add busybox-suid
RUN apk add -f tini bash build-base curl

# CREATE FUTURE VOLUME FOLDER WRITEABLE BY SCRAPY USER
RUN mkdir /backup && chown scrapy:scrapy /backup

# INIT NON ROOT USER CRON CRONTAB

COPY crontab /var/spool/cron/crontabs/scrapy
RUN chmod 0600 /var/spool/cron/crontabs/scrapy
RUN chown scrapy:scrapy /var/spool/cron/crontabs/scrapy

RUN touch /var/log/cron.log
RUN chown scrapy:scrapy /var/log/cron.log

# Switch to user SCRAPY already created in stage 1
WORKDIR /home/scrapy
USER scrapy

# SET TIMEZONE https://serverfault.com/questions/683605/docker-container-time-timezone-will-not-reflect-changes

VOLUME /backup

ENTRYPOINT ["/sbin/tini"]
CMD ["crond", "-f", "-l", "8", "-L", "/var/log/cron.log"]

通常情况下，crontab文件会在/backup卷文件夹中创建一个测试文件：

* * * * * touch /backup/testCRON

调试阶段:

• Login into my image with bash, it seems image correctly run the scrapy user :

  uid=1000(scrapy) gid=1000(scrapy) groups=1000(scrapy)
  

• The crontab -e command also gives the correct information

• But first error, cron don't run correctly, when i cat /var/log/cron.log i have a permission denied error

  crond: crond (busybox 1.27.2) started, log level 8
  crond: root: Permission denied
  crond: root: Permission denied
  

• I have also a second error when I try to write directly into the /backup folder using the command touch /backup/testFile. The /backup volume folder continue to be only accessible using root permission, don't know why.

- reyman64

Answer 1

crond 或 cron 应该作为 root 用户使用，正如此答案所述。

您可以查看aptible/supercronic，这是一个与 crontab 兼容的作业运行程序，专门设计用于在容器中运行。它将适应您创建的任何用户。

- VonC