Activate Python Virtualenv in Dockerfile

How to run a venv in the docker?

The example you show doesn't need any OS-level dependencies for Python dependency builds. That simplifies things significantly: you can do things in a single Docker build stage, without a virtual environment, and there wouldn't be any particular benefit from splitting it up.

FROM python:3.7
WORKDIR /app
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . .
CMD ["./bot.py"]

The place where a multi-stage build with a virtual environment helps is if you need a full C toolchain to build Python libraries. In this case, in a first stage, you install the C toolchain and set up the virtual environment. In the second stage you need to COPY --from=... the entire virtual environment to the final image.

# Builder stage:
FROM python:3.7 AS builder

# Install OS-level dependencies
RUN apt-get update \
 && DEBIAN_FRONTEND=noninteractive \
    apt-get install --no-install-recommends --assume-yes \
      build-essential
    # libmysql-client-dev, for example

# Create the virtual environment
RUN python3 -m venv /venv
ENV PATH=/venv/bin:$PATH

# Install Python dependencies
WORKDIR /app
COPY requirements.txt .
RUN pip3 install -r requirements.txt

# If your setup.py/setup.cfg has a console script entry point,
# install the application too
# COPY . .
# RUN pip3 install .

# Final stage:
FROM python:3.7 # must be _exactly_ the same image as the builder

# Install OS-level dependencies if needed (libmysqlclient, not ...-dev)
# RUN apt-get update && apt-get install ...

# Copy the virtual environment; must be _exactly_ the same path
COPY --from=builder /venv /venv
ENV PATH=/venv/bin:$PATH

# Copy in the application (if it wasn't `pip install`ed into the venv)
WORKDIR /app
COPY . .

# Say how to run it
EXPOSE 8000
CMD ["./bot.py"]

Dockerfile - activate Python virtualvenv - ubuntu

To explain your error message, it's because by default, Docker runs these commands with /bin/sh. source is a Bash command. You have two options:

1. Specify using Bash as the shell to run these commands by adding SHELL ["/bin/bash", "-c"] before the RUN commands
2. Use the dot operator: RUN . gnsave/bin/activate && pip install -r requirements.txt

Docker can't find Python venv executable

virtualenv is not standalone environment that can be copied between OSes (or containers):

$ python -m venv venv
$ ls -l venv/bin/

total 36
-rw-r--r-- 1 user user 1990 Jun  2 08:35 activate
-rw-r--r-- 1 user user  916 Jun  2 08:35 activate.csh
-rw-r--r-- 1 user user 2058 Jun  2 08:35 activate.fish
-rw-r--r-- 1 user user 9033 Jun  2 08:35 Activate.ps1
-rwxr-xr-x 1 user user  239 Jun  2 08:35 pip
-rwxr-xr-x 1 user user  239 Jun  2 08:35 pip3
-rwxr-xr-x 1 user user  239 Jun  2 08:35 pip3.10
lrwxrwxrwx 1 user user   46 Jun  2 08:35 python -> /home/user/.pyenv/versions/3.10.2/bin/python
lrwxrwxrwx 1 user user    6 Jun  2 08:35 python3 -> python
lrwxrwxrwx 1 user user    6 Jun  2 08:35 python3.10 -> python

As you can see python executables are just links to original python executable. It is something like snapshot for your original python that may be reverted or applied. But snapshot is useless if you don't have original base. So you have to create venv at same environment that will be used on.

However in case of containers you don't need venv at all. Container is already an isolated environment and you don't need one more isolation level with venv. (At least my question about why we need to use venv inside container is still don't have an answer)

In short: remove all venv related lines:

# syntax=docker/dockerfile:1

FROM gcr.io/distroless/python3
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
EXPOSE 5000
ENTRYPOINT [ "python" , "main.py"]

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However if you need to some extra libraries/compile tools (like gcc) to build python libraries when installing it by pip then venv may be used to be able move only resulted library binaries without store compile tools inside container.

In this case you have to use same (or compatible) python base at build image and resulted image (venv "snapshot" should be applied to compatible base).

Let's see this example:

FROM debian:11-slim AS build
...

FROM gcr.io/distroless/python3-debian11
...

Both images at least Debian based.

Or another example:

FROM python:3.9-slim as compiler
...

FROM python:3.9-slim as runner
...

And again base of builder and runner is the same

---

Looks like python:3.9.5-slim-buster and gcr.io/distroless/python3 are both Debian based and should be compatible, but probably it is not fully compatible.

You change endpoint to ENTRYPOINT [ "sleep" , "600"]. That will allow to keep container running for 10 minutes. After that attach to running container: docker exec -it container_name bash and check is python executable exists: ls -l /app/venv/bin/

_{or just simply use it without venv as I said before}

Error activating virtualenv with docker ENTRYPOINT script

The problem is your compose config, it's overriding /app_server with the directory from the host. Just delete the volumes from docker compose setup.

(As an aside, I recommend against using Alpine, it'll often result in slow Docker builds: https://pythonspeed.com/articles/alpine-docker-python/)

Is there a way to automatically activate a virtualenv as a docker entrypoint?

As an alternative to just sourcing the script inline with the command, you could make a script that acts as an ENTRYPOINT. An example entrypoint.sh would look something like:

#!/bin/bash
source venv/bin/activate
exec "$@"

Then in your Dockerfile you would copy this file and set it as the ENTRYPOINT:

FROM myimage
COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

Now you can run it like docker run mynewimage flask <sub command> or docker run mynewimage gunicorn.

Install and using pip and virtualenv in Docker

On Debian-based platforms, including Ubuntu, the command installed by python3-pip is called pip3 in order for it to peacefully coexist with any system-installed Python 2 and its pip.

Somewhat similarly, the virtualenv command is not installed by the package python3-virtualenv; to get that, you need apt-get install -y virtualenv.

Note that venv is included in the Python 3 standard library, so you don't really need to install anything at all.

python3 -m venv newenv

Why would you want a virtualenv inside Docker anyway, though? (There are situations where it makes sense but in the vast majority of cases, you want the Docker container to be as simple as possible, which means, install everything as root, and rebuild the whole container if something needs to be updated.)

As an aside, you generally want to minimize the number of RUN statements. Making many layers while debugging is perhaps defensible, but layers which do nothing are definitely just wasteful. Perhaps also discover that apt-get can install more than one package at a time.

RUN apt-get update -y && \
    apt-get install -y python3 python3-pip && \
    ...

The && causes the entire RUN sequence to fail as soon as one of the commands fails.

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