Docker Compose从Git仓库构建时无法找到Dockerfile的问题排查

树莓派4（Debian Bullseye系统，Docker版本24.0.7）环境下，尝试通过Docker Compose从包含Dockerfile的私有Git仓库构建容器，docker-compose.yml配置如下：

version: '3'

services:
  creideiki:
    build: 
      context: ssh://hab@haoke:22/data/Git/py_wunsch.git#main
      ssh:
        - default
    environment:
      - SSH_AUTH_SOCK=${SSH_AUTH_SOCK}
    volumes:
      - ${SSH_AUTH_SOCK}:${SSH_AUTH_SOCK}
    restart: always
    ports:
      - "3031:3031"

执行构建命令：

hab@tsht:/data/creideiki_test $ docker --log-level debug compose --progress=plain build

得到错误输出：

DEBU[0000] using default config store "/home/hab/.docker/buildx" 
#0 building with "default" instance using docker driver

#1 [creideiki internal] load git source ssh://hab@haoke:22/data/Git/py_wunsch.git#main
#1 0.252 Warning: Permanently added the ECDSA host key for IP address '192.168.2.8' to the list of known hosts.
#1 0.513 aa8cb0051360c52b27cf3781d6f6a07409c0d6ba       refs/heads/main
#1 DONE 0.7s

#1 [creideiki internal] load git source ssh://hab@haoke:22/data/Git/py_wunsch.git#main
#1 CACHED
DEBU[0000] using default config store "/home/hab/.docker/buildx" 
DEBU[0000] serving grpc connection                       
DEBU[0000] stopping session                              span="load buildkit capabilities"
DEBU[0000] serving grpc connection                       
DEBU[0002] stopping session                              
failed to solve: failed to read dockerfile: open /var/lib/docker/tmp/buildkit-mount2916653639/ssh:/hab@haoke:22/data/Git/py_wunsch.git#main/Dockerfile: no such file or directory

已知Git仓库根目录存在Dockerfile，且执行git clone -b main ssh://hab@haoke:22/data/Git/py_wunsch.git可成功克隆，本地克隆后能正常构建镜像，但Docker构建时提示找不到Dockerfile。

原因分析 #

从错误路径/var/lib/docker/tmp/buildkit-mount2916653639/ssh:/hab@haoke:22/data/Git/py_wunsch.git#main/Dockerfile可以看出，Docker没有正确将SSH URL识别为Git仓库地址，而是将其当作本地目录路径处理，导致无法定位仓库内的Dockerfile。

解决步骤 #

• 显式指定Dockerfile路径：在build配置中添加dockerfile: Dockerfile，强制Docker在克隆后的仓库根目录查找目标文件：

  build: 
    context: ssh://hab@haoke:22/data/Git/py_wunsch.git#main
    dockerfile: Dockerfile
    ssh:
      - default
  

• 简化Git SSH URL格式：使用Git标准SSH URL格式（省略默认22端口），避免Docker解析错误：

  context: hab@haoke:/data/Git/py_wunsch.git#main
  

• 升级Compose配置版本：将version: '3'改为version: '3.8'或更高版本，确保配置支持Git context的SSH认证特性。
• 强制启用BuildKit：构建时添加环境变量DOCKER_BUILDKIT=1，确保使用支持Git SSH context的构建引擎：

  DOCKER_BUILDKIT=1 docker compose --progress=plain build
  

内容的提问来源于stack exchange，提问作者Helmut