Add Dockerfile ARG for controlling Python deps (#1548)

Fixes #1530

.circleci/config.yml

@@ -133,11 +133,11 @@ jobs:
     steps:
       - checkout
       - setup_remote_docker
-      - restore_cache:
-          key: v1-{{.Branch}}
+      # We are not using the cached docker file here b/c we want the production
+      # build to use only the required Python files.
       - run:
-          name: Restore Docker image cache
-          command: docker load -i /tmp/docker.tar
+          name: Build Docker image
+          command: docker build -t app:build --build-arg PIP_FILE=build.txt .
       - run:
           name: Push image to Docker Hub
           command: |

Dockerfile

@@ -1,5 +1,9 @@
 FROM python:3.7.2-alpine
 
+# Default to building for local development.
+# Override with `--build-arg PIP_FILE=build.txt` to build for production.
+ARG PIP_FILE=all.txt
+
 EXPOSE 8000
 
 WORKDIR /app
@@ -23,7 +27,7 @@ COPY requirements/*.txt /tmp/requirements/
 # Switch to /tmp to install dependencies outside home dir
 WORKDIR /tmp
 # TODO: Consider a way to install only the "build.txt" deps for production.
-RUN pip install --require-hashes --no-cache-dir -r requirements/all.txt
+RUN pip install --require-hashes --no-cache-dir -r requirements/$PIP_FILE
 
 WORKDIR /app
 COPY . /app