Fix CI/CD pipeline: Use shell parameter expansion for env vars in CMD

- Replace explicit exports with shell parameter expansion in Dockerfile CMD
- Use defaults when environment variables aren't set
- Simplify GitHub Actions workflow to test with defaults
- Container now starts successfully with proper nginx configuration

Author: Robbie1977

.github/workflows/docker.yml

@@ -32,9 +32,9 @@ jobs:
     - name: Build test Docker image
       run: docker build --no-cache . --file Dockerfile --tag test-image
 
-    - name: Test Docker image
+    - name: Test container startup
       run: |
-        docker run -d --name test-container -e UPSTREAM_SERVER=owl.virtualflybrain.org:80 -e CACHE_MAX_SIZE=20g -e DNS_RESOLVER="8.8.8.8 1.1.1.1" test-image
+        docker run -d --name test-container test-image
         sleep 5
         if docker ps | grep -q test-container; then
           echo "Container is running successfully"

Dockerfile

@@ -16,4 +16,4 @@ RUN mkdir -p /var/cache/nginx && chown -R nginx:nginx /var/cache/nginx && \
 
 EXPOSE 80
 
-CMD ["/bin/sh", "-c", "export UPSTREAM_SERVER=$UPSTREAM_SERVER && export CACHE_MAX_SIZE=$CACHE_MAX_SIZE && export DNS_RESOLVER=\"$DNS_RESOLVER\" && envsubst '${UPSTREAM_SERVER} ${CACHE_MAX_SIZE} ${DNS_RESOLVER}' < /etc/nginx/nginx.conf.template > /etc/nginx/nginx.conf && /usr/local/bin/health-monitor.sh & nginx -g 'daemon off;'"]
+CMD ["/bin/sh", "-c", "UPSTREAM_SERVER=${UPSTREAM_SERVER:-owl.virtualflybrain.org:80} CACHE_MAX_SIZE=${CACHE_MAX_SIZE:-20g} DNS_RESOLVER=${DNS_RESOLVER:-8.8.8.8 1.1.1.1} envsubst '${UPSTREAM_SERVER} ${CACHE_MAX_SIZE} ${DNS_RESOLVER}' < /etc/nginx/nginx.conf.template > /etc/nginx/nginx.conf && /usr/local/bin/health-monitor.sh & nginx -g 'daemon off;'"]