There are terrible complications to having an entry point and a cmd in a dockerfile.

Dockerfile

@@ -25,7 +25,7 @@ COPY ./docker/substitute-env-variables.sh ./entrypoint.sh
 RUN chmod +x ./entrypoint.sh
 
 # Substitute environment variables in nginx configuration and index.html
-ENTRYPOINT ["./entrypoint.sh", \
+RUN ["./entrypoint.sh", \
             "/etc/nginx/html/index.html,/etc/nginx/conf.d/default.conf", \
             "PRODUCTION,API_URL,IRB_URL,HOME_ROUTE,BASE_HREF,PORT0", \
             "/etc/nginx/html"]