Error: pg_config executable not found when installing psycopg2 on Alpine in Docker

Question

I'm trying to build a Flask app using Postgres with Docker. I'd like to connect to an AWS RDS instance of Postgres, but use Docker for my Flask app. However, when trying to set up psycopg2 it runs into an error because it can't find pg_config. Here's the error:

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

Here's my Dockerfile:

FROM python:3.6.3-alpine3.6

WORKDIR /usr/src/app

COPY . .

RUN pip install -r requirements.txt

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

Many others seem to have a similar issue locally, but none of them involve using Docker. This seems like a Docker issue because I can set up a local virtual environment and the setup works just fine since I have Postgres installed locally and it's able to find my local pg_config.

It appears that during the container build/setup, Docker is trying to find pg_config within the container. Is there a way to install a pg_config in the container, even though I won't be using a containerized instance of Postgres, but rather the instance on RDS?

Any and all suggestions on how to get around this are welcomed.

Victoriavictorian

Possible duplicate of pg_config executable not found – Clayclaybank

These examples all seem to involve setting up locally, but not specifically within a Docker container that doesn't have Postgres installed. – Victoriavictorian

There's one answer for Alpine (see the first line of your Dockerfile): https://mcmap.net/q/24261/-pg_config-executable-not-found You should be able to abstract the answer for Docker. – Clayclaybank

Thanks @KlausD for pointing that out. Appreciate it. Will give it a try. – Victoriavictorian

Answer 1

Tested with Python 3.4.8, 3.5.5, 3.6.5 and 2.7.14 (just replace 3 with 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"]

Explanation: to build Psycopg you need the packages gcc musl-dev postgresql-dev. Then you also need that pg_config executable: while simply installing postgresql-dev will work, postgresql-libs does fine too and takes up some 12 MB less space.

---

Here's the original version of the answer (based on this Dockerfile) where I manually install Python onto a pure Alpine image because at that time Python did not provide the Docker image with Python 3.6 and Alpine 3.7. If you want to install Python 2.7 like that, also do apk add py2-pip (called py-pip in older Alpine repos).

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"]

Becoming

Thanks. It helped me with the same problem for python:3.6.4-alpine3.7 – Interdenominational

I used this Dockerfile but changed python3 to python2 (we still use 2.7.x) and I get an error: /usr/bin/python2: No module named pip. – Lavinia

@MikeStoddart I updated the answer, please see if it helps. – Becoming

For Ubuntu/Debian, install libpq-dev. See this SO answer. – Streeter

postgresql-libs depends on libpq, so you can use libpq instead pkgs.alpinelinux.org/package/edge/main/x86_64/postgresql-libs – Secessionist

Alpine 3.10.3: installing postgresql-libs did not solve the problem, but using postgresql-dev did. – Yvette

build-deps is not a valid package for recent versions (e.g. 3.11) of Alpine. – Striker

I am using "tiangolo/uvicorn-gunicorn:python3.8-slim" as my base image. I get "apk command not found". what do i do? – Pack

At least it got to install psycopg2 but there is an issue with purge. I get this error when I run the script above Usage: pip3 install [options] <requirement specifier> [package-index-options] ... pip3 install [options] -r <requirements file> [package-index-options] ... pip3 install [options] [-e] <vcs project url> ... pip3 install [options] [-e] <local project path> ... pip3 install [options] <archive url/path> ... no such option: --purge. The commands return a non-zero code: 2 – Hughhughes

To solve it, I did RUN \ apk update && \ apk add postgresql-dev gcc python3-dev musl-dev && \ <my_virtual_env>/bin/pip3 install -r requirements.txt. This successfully got pyscopg2 installed. – Hughhughes

@GitauHarrison It sounds like the command got mangled. --purge is a flag to apk, not pip. – Becoming

This failed for me today with an error about libffi while installing requirements.txt in a docker container. I was able to get it to work by adding `apk add --no-cache libffi-dev && ` to the beginning of the run command – Mountaineering

better to separately install psycopg2 and the rest of deps. to make the best out of docker cache. – Handlebar

Answer 2

Simply add these commands (psycopg2 dependencies) before installing dependencies from requirements.txt in Dockerfile

# install psycopg2 dependencies
RUN apk update
RUN apk add postgresql-dev gcc python3-dev musl-dev

Source: https://testdriven.io/blog/dockerizing-django-with-postgres-gunicorn-and-nginx/

Scramble

I was having an issue with purge from the solution example above. This was able to work for me – Hughhughes

Answer 3

I solved this by adding the following to my Dockerfile:

RUN apt-get update \
    && apt-get -y install libpq-dev gcc \
    && pip install psycopg2

this will install psycopg2 dependencies.

Worldly

This works for me. Im using macbook pro 14 inch m1 – Oscan

Works for python:slim Docker image as well – Yapok

Answer 4

You could try:

pip install psycopg2-binary

Terle

You still need to install postgres binaries, independently. – Kerekes

not at all. psycopg2-binary is not compatible with Alpine. – Whitacre

The psycopg2-binary package is meant for beginners to start playing with Python and PostgreSQL without the need to meet the build requirements. For production use you are advised to use the source distribution. Hence the need to use psycopg (without the binary) – Hughhughes

Answer 5

For development environment use the slim or full python image(not alpine), and instead of psycopg use psycopg2-binary. For production use psycopg with installing libpq-dev, gcc in Ubuntu.

Corn

Answer 6

On Python 3 you just need to do the following:

sudo apt install libpq-dev python3-dev

Misdate