Dockerfile COPY command not working as expected in Docker-compose - docker

Question

I'm trying to run Nginx through docker-compose to perform load balancing over Node.js back-end. I tried to ways:
Writing all configurations in docker-compose.yml while passing a nginx.conf as volume as follows:
version: '3'
services:
#nginx
nginx:
image: nginx
container_name: books-nginx
ports:
- 80:80
links:
- node1:node1
- node2:node2
- node3:node3
volumes:
- ./nginx/nginx.conf:/etc/nginx/nginx.conf
# Back-end
node1:
image: node
container_name: books-api1
ports:
- 3000
volumes:
- ./books-backend:/app
links:
- mongodb
environment:
- admin=admin-password
- secret=strong-password
command: bash -c "cd /app && npm install && npm start"
node2:
.
.
.
node3:
.
.
.
# MongoDB
mongodb:
image: mongo
container_name: books-mongo
ports:
- 27017
volumes:
- ./db/mongo:/data/db
In this case nginx runs perfectly.
Writing the configurations in a dockerfile inside 'nginx' directory and then starting it from docker-compose as follows:
nginx/Dockerfile:
FROM nginx
COPY nginx.conf /etc/nginx/nginx.conf
docker-compose:
#nginx
nginx:
build: ./nginx
container_name: books-nginx
ports:
- 80:80
links:
- node1:node1
- node2:node2
- node3:node3
But in this case whenever I send a request (eg. for admin authentication) to the back-end I get the following error:
books-nginx | 2017/07/31 22:19:33 [error] 6#6: *1 open() "/usr/share/nginx/html/api/admin/authenticate" failed (2: No such file or directory), client: 172.18.0.1, server: localhost, request: "POST /api/admin/authenticate HTTP/1.1", host: "localhost"
books-nginx | 172.18.0.1 - - [31/Jul/2017:22:19:33 +0000] "POST /api/admin/authenticate HTTP/1.1" 404 571 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.96 Safari/537.36" "-"
Any ideas on how to make the second way work like the first one (with COPY command) ?
Update
I tried creating the following dockerfile
FROM nginx
MAINTAINER Tamer Mohamed Bahgat
RUN rm -v /etc/nginx/nginx.conf
RUN rm /etc/nginx/conf.d/default.conf
ADD nginx/nginx.conf /etc/nginx/
RUN echo "daemon off;" >> /etc/nginx/nginx.conf
CMD service nginx start
and then creating the image separtely using docker build -t test-nginx . and using it in docker-compose.yml using image: test-nginx . It worked and gave no errors.
But, using build: . (. is the location of the same dockerfile) still gives me the same error.