nginx conditional proxy: invalid number of arguments in “try_files” directive

Question

I have nginx used as a proxy for a handful of web services, running in a docker container, using the config below. I have the configuration to 90% of where it needs to be, but the problems for the last little bit are confounding me. Running this config results in the error message nginx: [emerg] invalid number of arguments in "try_files" directive in /etc/nginx/nginx.conf:75. This corresponds to this chunk of the config:

location / {
  try_files $uri @proxy_to_appserver;  # <--- this is line 75
}
location @proxy_to_appserver {
  proxy_pass http://appserver/;
}

This is attempting to have nginx handle requests for static resources, e.g. request for images/cat.gif would look for a cat picture in the web root, and send the request to the appserver if none was found. All the documentation I have found has essentially this same syntax, using the $uri variable followed by a named location for the proxy. But something else in the config must be turning this into an invalid syntax, or there is something else obvious that I cannot see after staring at config files for too long.

Full config file follows. I'm using the official nginx:1.11 docker image, fwiw.

worker_processes 4;

events {
  worker_connections 1024;
}

http {
  include mime.types;
  default_type application/octet-stream;

  upstream appserver {
    server appserver:8000;
  }
  upstream rabbitmq {
    server rabbitmq:15672;
  }
  upstream solr {
    server solr:8983;
  }
  upstream flower {
    server flower:5555;
  }

  ssl_session_cache shared:SSL:10m;
  ssl_session_timeout 10m;
  ssl_session_tickets off;

  server {
    listen  80 default_server;
    listen  [::]:80 default_server;
    return  301 https://$host$request_uri;
  }

  server {
    listen                    443 ssl http2;
    listen                    [::]:443 ssl http2;

    ssl_certificate           /etc/ssl/my_application/certificate.chained.crt;
    ssl_certificate_key       /etc/ssl/my_application/certificate.key;

    ssl_dhparam               /etc/ssl/my_application/dhparam.pem;

    ssl_protocols             TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers               'ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS';
    ssl_prefer_server_ciphers on;

    # OCSP Stapling
    ssl_stapling              on;
    ssl_stapling_verify       on;
    ssl_trusted_certificate   /etc/ssl/my_application/trustchain.crt;
    resolver                  131.243.5.1 8.8.8.8 8.8.4.4;

    # HSTS header (15768000 == 6 months)
    add_header  Strict-Transport-Security max-age=15768000;

    client_body_buffer_size     10k;
    client_header_buffer_size   1k;
    client_max_body_size        50m;
    large_client_header_buffers 2 1k;

    client_body_timeout   12;
    client_header_timeout 12;
    keepalive_timeout     5;
    send_timeout          10;

    gzip             on;
    gzip_comp_level  2;
    gzip_min_length  1000;
    gzip_proxied     expired no-cache no-store private auth;
    gzip_types       text/plain text/css text/xml text/javascript application/javascript application/json application/x-javascript application/xml application/xml+rss;

    root /var/www;

    location / {
      try_files $uri @proxy_to_appserver;  # <--- this is line 75
    }
    location @proxy_to_appserver {
      proxy_pass http://appserver/;
    }

    location /flower {
      return 301 /flower/;
    }
    location /flower/ {
      proxy_pass http://flower/;
    }

    location /rabbitmq {
      return 301 /rabbitmq/;
    }
    location /rabbitmq/ {
      proxy_pass http://rabbitmq/;
    }

    location /solr {
      return 301 /solr/;
    }
    location /solr/ {
      proxy_pass http://solr/solr/;
    }

    error_page 500 502 503 504 /static/500.html;
  }
}

Update: for any from the future finding this… I ended up getting rid of try_files and the named location entirely. The problem section around line 75 is replaced with this:

location /static {
}
location /uploads {
}
location / {
  proxy_pass http://appserver/;
}

This works because all the files used by the appserver container are either under /var/www/static or /var/www/uploads. This also mirrors the layout for proxies to the other services, so the config remains simple.

Answer 1

According to the comments:

• Contrary to what I wrote in the comments, this directive try_files $uri @proxy_to_appserver is valid and fine. I've just checked and tested this.

• Removing the trailing / from the proxy_pass http://appserver/ directive solved this:

  nginx: [emerg] "proxy_pass" cannot have URI part in location given by regular expression, or inside named location, or inside "if" statement, or inside "limit_except" block in /etc/nginx/nginx.conf:78