Nginx proxy and docker 502 bad gateway - docker

Question

I have two Docker containers on the same network. One of them is a Spring Boot server app, the other is a React client app. I'm trying to get the client to make AJAX calls to the server. When I run them both locally on my machine, outside of Docker, everything works. When I run them with my docker configuration and using an Nginx proxy, I get 502 bad gateway errors.
Here is my docker-compose configuration:
version: '3'
video-server:
build:
context: .
dockerfile: video-server_Dockerfile
container_name: video-server
networks:
- videoManagerNetwork
environment:
- VIDEO_MANAGER_DIR=/opt/videos
volumes:
- ${VIDEO_MANAGER_DIR_PROD}:/opt/videos
video-client:
build:
context: .
dockerfile: video-client_Dockerfile
container_name: video-client
networks:
- videoManagerNetwork
ports:
- 9000:80
networks:
videoManagerNetwork:
As you can see, both containers are given explicit names and are on the same network. video-client is the Nginx React app, video-server is the Spring Boot app.
Here is my Nginx config:
worker_processes auto;
events {
worker_connections 8000;
multi_accept on;
}
http {
log_format compression '$remote_addr - $remote_user [$time_local] '
'"$request" $status $upstream_addr '
'"$http_referer" "$http_user_agent"';
include /etc/nginx/mime.types;
default_type text/plain;
server {
listen 80;
# TODO make sure the log is written to a docker volume
access_log /var/log/nginx/access.log compression;
root /var/www;
index index.html;
location / {
try_files $uri $uri/ /index.html;
}
location /api/ {
proxy_set_header Host $http_host;
proxy_pass http://video-server:8080/api/;
}
location ~* \.(?:jpg|jpeg|gif|png|ico|cur|gz|svg|svgz|mp4|ogg|ogv|webm|htc)$ {
expires 1M;
access_log off;
add_header Cache-Control "public";
}
location ~* \.(?:css|js)$ {
try_files $uri =404;
expires 1y;
access_log off;
add_header Cache-Control "public";
}
location ~ ^.+\..+$ {
try_files $uri =404;
}
}
}
As you can see, I'm proxying all calls to /api/ to my video-server container. This should be working. I even shelled into the video-client container docker exec -it video-client bash, installed curl, and was able to successfully make calls to the other container, ie http://video-server:8080/api/categories.
I'm looking for suggestions about what the problem with my configuration could be. I'm not particularly experienced with Nginx, so I'm assuming I'm doing something wrong there.
Edit
I finally figured out what was necessary to make this work. I would still be interested to understand why this helps.
I added the following lines to the "http" section of the Nginx config, and the problem was solved:
fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;
fastcgi_connect_timeout 300;
fastcgi_send_timeout 300;
fastcgi_read_timeout 300;
So it looks like this changed the buffer and timeout settings. Why did this help?