Custom Discovery Server ======================= Description ----------- This guide assumes that you have already set up Syncthing. If you haven't yet, head over to :ref:`getting-started` first. Installing ---------- Go to `releases `__ and download the file appropriate for your operating system. Unpacking it will yield a binary called ``discosrv`` (or ``discosrv.exe`` on Windows). Start this in whatever way you are most comfortable with; double clicking should work in any graphical environment. At first start, discosrv will generate the directory ``/var/discosrv`` (``X:\var\discosrv`` on Windows, where X is the partition ``discosrv.exe`` is executed from) with configuration. If the user running ``discosrv`` doesn't have permission to do so, create the directory and set the owner appropriately or use the command line switches (see below) to select a different location. Configuring ----------- .. note:: If you are running an instance of syncthing on the discovery server, you must either add that instance to other nodes using a static address or bind the discovery server and syncthing instances to different IP addresses. Running discosrv with non-default settings requires passing the respective parameters to discosrv on every start. ``discosrv -help`` gives you all the tweakables with their defaults: :: Usage of discosrv: -cert string Certificate file (default "cert.pem") -db-backend string Database backend to use (default "ql") -db-dsn string Database DSN (default "memory://discosrv") -debug Debug -http Listen on HTTP (behind an HTTPS proxy) -key string Key file (default "key.pem") -limit-avg int Allowed average package rate, per 10 s (default 5) -limit-burst int Allowed burst size, packets (default 20) -limit-cache int Limiter cache entries (default 10240) -listen string Listen address (default ":8443") -stats-file string File to write periodic operation stats to Certificates ^^^^^^^^^^^^ The discovery server provides service over HTTPS. To ensure secure connections from clients there are three options: - Use a CA-signed certificate pair for the domain name you will use for the discovery server. This is like any other HTTPS website; clients will authenticate the server based on it's certificate and domain name. - Use any certificate pair and let clients authenticate the server based on it's "device ID" (similar to Syncthing-to-Syncthing authentication). In this case, using ``syncthing -generate`` is a good option to create a certificate pair. - Pass the ``-http`` flag if the discovery server is behind an SSL-secured reverse proxy. See below for configuration. For the first two options, the discovery server must be given the paths to the certificate and key at startup. This isn't necessary with the ``http`` flag:: $ discosrv -cert /path/to/cert.pem -key /path/to/key.pem Server device ID is 7DDRT7J-UICR4PM-PBIZYL3-MZOJ7X7-EX56JP6-IK6HHMW-S7EK32W-G3EUPQA The discovery server prints it's device ID at startup. In the case where you are using a non CA signed certificate, this device ID (fingerprint) must be given to the clients in the discovery server URL:: https://disco.example.com:8443/v2/?id=7DDRT7J-UICR4PM-PBIZYL3-MZOJ7X7-EX56JP6-IK6HHMW-S7EK32W-G3EUPQA Otherwise, the URL (note the trailing slash after the ``v2``) will be:: https://disco.example.com:8443/v2/ Pointing Syncthing at Your Discovery Server ------------------------------------------- By default, Syncthing uses a number of global discovery servers, signified by the entry ``default`` in the list of discovery servers. To make Syncthing use your own instance of discosrv, open up Syncthing's web GUI. Go to settings, Global Discovery Server and add discosrv's host address to the comma-separated list, e.g. ``https://disco.example.com:8443/v2/``. Note that discosrv uses port 8443 by default. For discosrv to be available over the internet with a dynamic IP address, you will need a dynamic DNS service. If you wish to use *only* your own discovery server, remove the ``default`` entry from the list. Reverse Proxy Setup ------------------- The discovery server can be run behind an SSL-secured reverse proxy. This allows: - Use of a subdomain name without requiring a port number added to the URL - Sharing an SSL certificate with multiple services on the same server Requirements ^^^^^^^^^^^^ - Run the discovery server using the -http flag :code:`discosrv -http`. - SSL certificate/key configured for the reverse proxy - The "X-Forwarded-For" http header must be passed through with the client's real IP address - The "X-SSL-Cert" must be passed through with the PEM-encoded client SSL certificate - The proxy must request the client SSL certificate but not require it to be signed by a trusted CA. Nginx ^^^^^ These three lines in the configuration take care of the last three requirements listed above: .. code-block:: nginx proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-SSL-Cert $ssl_client_cert; ssl_verify_client optional_no_ca; The following is a complete example Nginx configuration file. With this setup, clients can use https://discovery.mydomain.com as the discovery server URL in the Syncthing settings. .. code-block:: nginx # HTTP 1.1 support proxy_http_version 1.1; proxy_buffering off; proxy_set_header Host $http_host; proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection $proxy_connection; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $proxy_x_forwarded_proto; proxy_set_header X-SSL-Cert $ssl_client_cert; upstream discovery.mydomain.com { # Local IP address:port for discovery server server 172.17.0.6:8443; } server { server_name discovery.mydomain.com; listen 80; access_log /var/log/nginx/access.log vhost; return 301 https://$host$request_uri; } server { server_name discovery.mydomain.com; listen 443 ssl http2; access_log /var/log/nginx/access.log vhost; ssl_protocols TLSv1 TLSv1.1 TLSv1.2; ssl_ciphers ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384: DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:E CDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA25 6:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA3 84:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS -DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA; ssl_prefer_server_ciphers on; ssl_session_timeout 5m; ssl_session_cache shared:SSL:50m; ssl_certificate /etc/nginx/certs/discovery.mydomain.com.crt; ssl_certificate_key /etc/nginx/certs/discovery.mydomain.com.key; ssl_dhparam /etc/nginx/certs/discovery.mydomain.com.dhparam.pem; add_header Strict-Transport-Security "max-age=31536000"; ssl_verify_client optional_no_ca; location / { proxy_pass http://discovery.mydomain.com; } } An example of automating the SSL certificates and reverse-proxying the Discovery Server and Syncthing using Nginx, `Let's Encrypt`_ and Docker can be found here_. .. _Let's Encrypt: https://letsencrypt.org/ .. _here: https://forum.syncthing.net/t/docker-syncthing-and-syncthing-discovery-behind-nginx-reverse-proxy-with-lets-encrypt/6880