Remove old compiled spt3g/so3g layers from Docker image (#397)

* Switch to directly using ubuntu:22.04 base image

This cuts out the spt3g-docker and so3g layers in the image build. ocs will
pull in so3g from pip, these extra layers were from when we needed to compile
spt3g_software and so3g prior to so3g becoming pip installable.

* Setup and use virtualenv within image

* Update pip within venv

* Document use of virtualenv in developers page about Docker

* Replace lingering python3 with python

Dockerfile

@@ -2,7 +2,11 @@
 # A container setup with an installation of ocs.
 
 # Use ubuntu base image
-FROM simonsobs/so3g:v0.1.3-13-g5471f0d
+FROM ubuntu:22.04
+
+# Set timezone to UTC
+ENV TZ=Etc/UTC
+RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
 
 # Set locale
 ENV LANG C.UTF-8
@@ -22,26 +26,35 @@ ENV OCS_CONFIG_DIR=/config
 ENV PYTHONUNBUFFERED=1
 
 # Install python and pip
-RUN apt-get update && apt-get install -y python3 \
+RUN apt-get update && apt-get install -y \
+    git \
+    python3 \
     python3-pip \
+    python3-virtualenv \
+    python-is-python3 \
     vim
 
+# Setup virtualenv
+RUN python -m virtualenv /opt/venv/
+ENV PATH="/opt/venv/bin:$PATH"
+RUN python -m pip install -U pip
+
 # Install init system
-RUN pip3 install dumb-init
+RUN python -m pip install dumb-init
 
 # Copy in and install requirements
 # This will leverage the cache for rebuilds when modifying OCS, avoiding
 # downloading all the requirements again
 COPY requirements/ /app/ocs/requirements
 COPY requirements.txt /app/ocs/requirements.txt
 WORKDIR /app/ocs/
-RUN pip3 install -r requirements.txt
+RUN python -m pip install -r requirements.txt
 
 # Copy the current directory contents into the container at /app
 COPY . /app/ocs/
 
 # Install ocs
-RUN pip3 install .
+RUN python -m pip install .
 
 # Reset workdir to avoid local imports
 WORKDIR /

docs/developer/docker.rst

@@ -26,6 +26,12 @@ OCS Agent via ``ocs-agent-cli``. See the `Dockerfile reference
 <https://docs.docker.com/engine/reference/builder/>`_ in the Docker
 documentation for more information about how to write a Dockerfile.
 
+.. note::
+
+    ``ocs`` and its dependencies are installed into a ``virutualenv`` kept in
+    ``/opt/venv/``. This is enabled by putting ``/opt/venv/bin/`` at the front of
+    the PATH. This is in place to isolate the installation from the system Python.
+
 Building Upon the Base Image
 ----------------------------
 
@@ -43,19 +49,18 @@ that looks something like:
 
     # Install required dependencies
     RUN apt-get update && apt-get install -y rsync \
-        wget \
-        python3-pip
+        wget
 
     # Copy in and install requirements
     COPY requirements.txt /app/my-ocs-agent/requirements.txt
     WORKDIR /app/my-ocs-agent/
-    RUN pip3 install -r requirements.txt
+    RUN python -m pip install -r requirements.txt
 
     # Copy the current directory contents into the container at /app
     COPY . /app/my-ocs-agent/
 
     # Install my-ocs-agent
-    RUN pip3 install .
+    RUN python -m pip install .
 
     # Run agent on container startup
     ENTRYPOINT ["dumb-init", "ocs-agent-cli"]