# Frontend Proxy server that:
# 1. Acts as the HTTPS proxy termination point.
# 2. Forwards BDB POST requests to OpenResty backend after appending the app_id
#    and app_key headers.
# 3. Forwards BDB GET requests to BDB backend.
# 4. Does health check with LB.

worker_processes 4;
daemon off;
user nobody nogroup;
pid /tmp/nginx.pid;
error_log /dev/stderr;

events {
  # Each worker handles up to 1024 connections. Increase this for heavy
  # workloads.
  worker_connections 1024;
  accept_mutex on;
  use epoll;
}

http {
  access_log /dev/stdout combined buffer=16k flush=5s;

  # Allow 2048 req/sec from the same IP address, and store the counters in a
  # `zone` or shared memory location tagged as 'one'.
  limit_req_zone $binary_remote_addr zone=one:10m rate=2048r/s;

  # Enable logging when requests are being throttled.
  limit_req_log_level notice;

  # HTTP status code that is returned to the client; 429 is for TooManyRequests,
  # ref. RFC 6585
  limit_req_status 429;

  # Limit requests from the same client, allow `burst` to 3072 r/s,
  # `nodelay` or drop connection immediately in case it exceeds this
  # threshold.
  limit_req zone=one burst=3072 nodelay;

  # `slowloris` attack mitigation settings.
  client_body_timeout 30s;
  client_header_timeout 10s;

  # DNS resolver to use for all the backend names specified in this configuration.
  resolver DNS_SERVER valid=30s ipv6=off;

  keepalive_timeout 60s;

  # The following map blocks enable lazy-binding to the backend at runtime,
  # rather than binding as soon as NGINX starts.
  map $remote_addr $bdb_backend {
    default BIGCHAINDB_BACKEND_HOST;
  }
  map $remote_addr $openresty_backend {
    default OPENRESTY_BACKEND_HOST;
  }

  # Frontend server for the external clients; acts as HTTPS termination point.
  server {
    listen PROXY_FRONTEND_PORT ssl;
    server_name "PROXY_FQDN";
    ssl_certificate        /etc/nginx/ssl/cert.pem;
    ssl_certificate_key    /etc/nginx/ssl/cert.key;
    ssl_protocols          TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers            HIGH:!aNULL:!MD5;

    underscores_in_headers on;

    # No websocket support for web proxy
    location /api/v1/streams/valid_transactions {
      return 403 'Websockets are not supported in the web proxy';
    }

    # Forward other URL paths as per business logic/use case to BDB or
    # OpenResty instance.
    location / {
      proxy_ignore_client_abort on;
      proxy_set_header X-Real-IP  $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

      # max client request body size: avg transaction size.
      client_max_body_size 15k;

      # Debug block for listing all the headers sent with the request
      header_filter_by_lua_block {
        local h = ngx.req.get_headers()
        for k, v in pairs(h) do
          ngx.log(ngx.ERR, "Header "..k..": "..v..";")
        end
      }

      # check if the request has the expected origin header
      if ($http_origin !~ "PROXY_EXPECTED_ORIGIN_HEADER" ) {
        return 403 'Unknown origin';
      }

      if ($request_method = 'OPTIONS') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range,app_key,app_id';
        add_header 'Access-Control-Max-Age' 43200;
        add_header 'Content-Type' 'text/plain charset=UTF-8';
        add_header 'Content-Length' 0;
        add_header 'Referrer-Policy' "PROXY_REFERRER_POLICY";
        return 204;
      }

      # check if the request originated from the required web page
      # use referer header.
      if ($http_referer !~ "PROXY_EXPECTED_REFERER_HEADER" ) {
        return 403 'Unknown referer';
      }

      # No auth for GETs, forward directly to BDB.
      if ($request_method = GET) {
        proxy_pass http://$bdb_backend:BIGCHAINDB_API_PORT;
      }

      # POST requests get forwarded to OpenResty instance; set the correct
      # headers accordingly
      proxy_set_header  app_id "PROXY_APP_ID";
      proxy_set_header  app_key "PROXY_APP_KEY";
      if ($request_method = POST ) {
        proxy_pass http://$openresty_backend:OPENRESTY_BACKEND_PORT;
      }
    }
  }

  # Frontend server for the load balancer to respond to health checks.
  server {
    listen HEALTH_CHECK_PORT;

    location = /health {
      return 200;
    }
  }
}