Reverse proxy

Reverse proxy#

The location directive, used within the server context, specifies how NGINX should process requests based on the URI.

More in correspoding section of the official documentation.

Setup#

It turns out that it’s quite a complex task to build examples that show how everything works, so this section describes what we need to show everything. In summary, we need

  • Proxied server - server where we’ll redirect requests to nginx.

  • And nginx, which can be configured differently for different examples.

  • A network that connects containers.

The following cell creates a Docker Compose file that satisfies all these requirements.

cat << EOF > reverse_proxy_files/docker-compose.yml
services:
  proxied:
    image: kennethreitz/httpbin
    container_name: client_container
    ports: 
      - 81:80
  nginx:
    image: nginx
    container_name: experiment_nginx
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf
    ports: 
      - 80:80
EOF

The following cell runs applications.

docker compose -f reverse_proxy_files/docker-compose.yml up -d &> /dev/null

Note Don’t forget to clear the environment.

docker compose -f reverse_proxy_files/docker-compose.yml down &> /dev/null

Proxy pass#

Find out more in:

proxy_path in nginx specify the URL of the proxied service. This would be a URL that nginx will request.

The following example defines location /recsys and ties to it http://client_container/anything/config/.

cat << EOF > reverse_proxy_files/nginx.conf
events {}
http {
    server {
        listen 80;
        location /recsys {
            proxy_pass "http://client_container/anything/config/";
        }
    }
}
EOF

docker exec -it experiment_nginx nginx -s reload

2024/09/09 08:06:03 [notice] 30#30: signal process started

The following cell demonstrates a request to the <nginx address>/recsys/..., which uses httpbin to display the result of the request.

curl -L http://localhost:80/recsys/101

{
  "args": {}, 
  "data": "", 
  "files": {}, 
  "form": {}, 
  "headers": {
    "Accept": "*/*", 
    "Connection": "close", 
    "Host": "client_container", 
    "User-Agent": "curl/7.81.0"
  }, 
  "json": null, 
  "method": "GET", 
  "origin": "172.19.0.2", 
  "url": "http://client_container/anything/config//101"
}

In the url field you can check the exact url that nginx throws to the httpbin.

Headers to server (proxy_set_header)#

Allows redefining or appending fields to the request header passed to the proxied server. You can add aditional headers to the http request that will be sent to the destination server. So by using syntax proxy_set_header <header field> <value>;.

The following example changes the nginx config to add two new fields to the http header Name and SecondName and reloads nginx.

docker exec -i experiment_nginx sh -c 'cat >  /etc/nginx/nginx.conf' << EOF
events {}
http {
    server {
        listen 80;
        location / {
            proxy_pass "http://client_container/headers";
            proxy_set_header Name Fedor;
            proxy_set_header SecondName Kobak;
        }
    }
}
EOF

docker exec -it experiment_nginx nginx -s reload

2024/09/09 07:44:06 [notice] 44#44: signal process started

First, consider what happens if we just request httpbin directly.

curl http://localhost:81/headers

{
  "headers": {
    "Accept": "*/*", 
    "Host": "localhost:81", 
    "User-Agent": "curl/7.81.0"
  }
}

There are no additional headers - just the very basic ones generated by curl.

curl http://localhost:80

{
  "headers": {
    "Accept": "*/*", 
    "Connection": "close", 
    "Host": "client_container", 
    "Name": "Fedor", 
    "Secondname": "Kobak", 
    "User-Agent": "curl/7.81.0"
  }
}

If you compare the output of the original and proxied requests, you can see that the proxied requests have additional headers - just as we specified in the nginx configuration.

Cache#

Nginx provides a caching facility that saves responses from proxied URLs and reuses them later. You can enable and configure it using directives that start with proxy_cache. There is a special tutorial on the Nginx website that covers Nginx configuration.

Check:

The following cell defines two locations, /cached and /no_cached, both proxying to the same httpbin URL that returns a specified number of random bytes. The /cached location uses caching, while /no_cached does not.

To achieve this, the following directives are used:

  • proxy_cache_path /var/cache/nginx/proxy_cache keys_zone=my_cache:10m;:

    • Sets /var/cache/nginx/proxy_cache as the folder for cache.

    • Defines my_cache as the cache zone name to be used later.

    • Specifies that my_cache can contain up to 10 megabytes of cache.

  • proxy_cache my_cache specifies that the my_cache cache zone should be used for the corresponding context.

  • proxy_cache_valid 200 10m; configures the system to save responses with a status code of 200 for 10 minutes.

cat << EOF > reverse_proxy_files/nginx.conf
events {}
http {

    proxy_cache_path /var/cache/nginx/proxy_cache keys_zone=my_cache:10m;

    server {
        listen 80;

        location /cached {
            proxy_cache my_cache;
            proxy_cache_valid 200 10m;

            proxy_pass http://client_container/bytes/50;
        }

        location /no_cached {proxy_pass http://client_container/bytes/50;}
    }
}
EOF

docker exec -it experiment_nginx nginx -s reload

2024/09/09 09:26:45 [notice] 80#80: signal process started

Now let’s try to request the /cached location twice.

echo $(curl -s localhost:80/cached)
echo $(curl -s localhost:80/cached)

v24� ޷�˯[��#`h�7Dv�}(�b�-V����G�1H[!��}ß�
v24� ޷�˯[��#`h�7Dv�}(�b�-V����G�1H[!��}ß�

So we got the same response both times, indicating that the answer was cached.

Now let’s try to request the /no_cached location to show the difference.

echo $(curl -s localhost:80/no_cached)
echo $(curl -s localhost:80/no_cached)

f���� �=�a�e�[�4y89et�����j�]�۵u���/f"8
&�N�WE�'���R0/�l佟�@�@�q��{K��

Each response differs from the previous one, showing that the /no_cached location does not use caching.