错误：在Docker的Alpine上安装psycopg2时找不到pg_config可执行文件

Question

我正在尝试将Postgres与Docker一起构建Flask应用程序。我想连接到Postgres的AWS
RDS实例，但是将Docker用于我的Flask应用程序。但是，在尝试设置时psycopg2会遇到错误，因为找不到pg_config。这是错误：

Building api
Step 1/5 : FROM python:3.6.3-alpine3.6
 ---> 84c98ca3b5c5
Step 2/5 : WORKDIR /usr/src/app
 ---> Using cache
 ---> 407c158f5ee4
Step 3/5 : COPY . .
 ---> 966df18d329e
Step 4/5 : RUN pip install -r requirements.txt
 ---> Running in 284cc97aeb63
Collecting aniso8601==1.3.0 (from -r requirements.txt (line 1))
  Downloading aniso8601-1.3.0.tar.gz (57kB)
Collecting click==6.7 (from -r requirements.txt (line 2))
  Downloading click-6.7-py2.py3-none-any.whl (71kB)
Collecting Flask==0.12.2 (from -r requirements.txt (line 3))
  Downloading Flask-0.12.2-py2.py3-none-any.whl (83kB)
Collecting Flask-RESTful==0.3.6 (from -r requirements.txt (line 4))
  Downloading Flask_RESTful-0.3.6-py2.py3-none-any.whl
Collecting Flask-SQLAlchemy==2.3.2 (from -r requirements.txt (line 5))
  Downloading Flask_SQLAlchemy-2.3.2-py2.py3-none-any.whl
Collecting itsdangerous==0.24 (from -r requirements.txt (line 6))
  Downloading itsdangerous-0.24.tar.gz (46kB)
Collecting Jinja2==2.9.6 (from -r requirements.txt (line 7))
  Downloading Jinja2-2.9.6-py2.py3-none-any.whl (340kB)
Collecting MarkupSafe==1.0 (from -r requirements.txt (line 8))
  Downloading MarkupSafe-1.0.tar.gz
Collecting psycopg2==2.7.3.1 (from -r requirements.txt (line 9))
  Downloading psycopg2-2.7.3.1.tar.gz (425kB)
    Complete output from command python setup.py egg_info:
    running egg_info
    creating pip-egg-info/psycopg2.egg-info
    writing pip-egg-info/psycopg2.egg-info/PKG-INFO
    writing dependency_links to pip-egg-info/psycopg2.egg-info/dependency_links.txt
    writing top-level names to pip-egg-info/psycopg2.egg-info/top_level.txt
    writing manifest file 'pip-egg-info/psycopg2.egg-info/SOURCES.txt'
    Error: pg_config executable not found.

    Please add the directory containing pg_config to the PATH
    or specify the full executable path with the option:

        python setup.py build_ext --pg-config /path/to/pg_config build ...

    or with the pg_config option in 'setup.cfg'.

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-01lf5grh/psycopg2/
ERROR: Service 'api' failed to build: The command '/bin/sh -c pip install -r requirements.txt' returned a non-zero code: 1

这是我的Dockerfile：

FROM python:3.6.3-alpine3.6

WORKDIR /usr/src/app

COPY . .

RUN pip install -r requirements.txt

CMD ["python", "app.py"]

许多其他问题在本地似乎也有类似的问题，但没有一个涉及使用Docker。
这似乎是一个Docker问题，因为我可以设置本地虚拟环境，并且安装正常，因为我在本地安装了Postgres，并且可以在本地找到我pg_config。

看来在容器构建/设置期间，Docker试图pg_config在容器内查找。pg_config即使我不会使用Postgres的容器化实例，而是使用RDS上的实例，是否可以在容器中安装？

欢迎提供有关如何解决此问题的任何建议。谢谢！

Answer 1

经过Python 3.4.8、3.5.5、3.6.5和2.7.14的测试（只需将3替换为2）：

# You can use a specific version too, like python:3.6.5-alpine3.7
FROM python:3-alpine

WORKDIR /usr/src/app

COPY requirements.txt .

RUN \
 apk add --no-cache postgresql-libs && \
 apk add --no-cache --virtual .build-deps gcc musl-dev postgresql-dev && \
 python3 -m pip install -r requirements.txt --no-cache-dir && \
 apk --purge del .build-deps

COPY . .

CMD ["python3", "app.py"]

说明：要构建Psycopg，您需要安装软件包gcc musl-dev postgresql- dev。然后，您还需要pg_config可执行文件：虽然可以简单地安装postgresql-dev，postgresql- libs但也可以正常工作，并且占用的空间少12 MB。

这是答案的原始版本（基于Dockerfile），在该版本中，我手动将Python安装到纯Alpine映像上，因为那时Python并未提供Python
3.6和Alpine 3.7的Docker映像。如果要这样安装Python 2.7，也可以这样做apk add py2-pip（py- pip在较早的Alpine仓库中称为）。

FROM alpine:3.7

WORKDIR /usr/src/app

COPY requirements.txt .

RUN \
 apk add --no-cache python3 postgresql-libs && \
 apk add --no-cache --virtual .build-deps gcc python3-dev musl-dev postgresql-dev && \
 python3 -m pip install -r requirements.txt --no-cache-dir && \
 apk --purge del .build-deps

COPY . .

CMD ["python3", "app.py"]