feat: add development docker compose configuration

Add a simple docker compose configuration which can be used to test the
application in local development.

Dockerfile

+###################################################################################################
+# Image used to build frontend.
 FROM node:lts AS frontend-builder
 
 WORKDIR /usr/src/app
@@ -10,7 +12,9 @@ RUN yarn config set network-timeout 600000 -g && yarn install
 COPY ./frontend/ .
 RUN yarn build
 
-FROM registry.gitlab.developers.cam.ac.uk/uis/devops/infra/dockerimages/django:4.2-py3.11-alpine AS base
+###################################################################################################
+# Production image
+FROM registry.gitlab.developers.cam.ac.uk/uis/devops/infra/dockerimages/django:4.2-py3.11-alpine AS production
 ENV PYTHONUNBUFFERED=1 PYTHONDONTWRITEBYTECODE=1
 
 WORKDIR /usr/src/app
@@ -19,4 +23,5 @@ RUN --mount=type=bind,target=/context pip install /context
 COPY --from=frontend-builder /usr/src/app/build/ ./frontend/build/
 
 ENV GATEWAY_CONSOLE_UI_DIR=/usr/src/app/frontend/build
+
 ENTRYPOINT ["api-gateway-emulator"]

README.md

@@ -8,8 +8,15 @@ which forward requests to the URL pointed to by the
 
 A proxy configuration UI is at port 9001.
 
-Initial proxy configuration can be influenced by other `GATEWAY_...`
-environment variables.
+Initial proxy configuration can be influenced by other `GATEWAY_...` environment variables. See the
+[definition of the Settings class](./api_gateway_emulator/__init__.py).
+
+## Backend development
+
+You can start a simple development instance via `docker compose up --build`. **CHANGES ARE NOT HOT
+RELOADED.** If you make a change, you will need to restart the server via `docker compose down` and
+`docker compose up --build`. The proxied application is a simple echo server which returns details
+of the incoming request as a JSON document.
 
 ## Frontend development
 

docker-compose.yaml

+services:
+  proxy:
+    build:
+      context: .
+    ports:
+      - 9000:9000
+      - 9001:9001
+    depends_on:
+      - echo
+    environment:
+      GATEWAY_PROXY_DESTINATION_URL: http://echo:80/
+
+  echo:
+    image: ealen/echo-server