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Using a forward proxy with Synapse

You can use Synapse with a forward or outbound proxy. An example of when this is necessary is in corporate environments behind a DMZ (demilitarized zone). Synapse supports routing outbound HTTP(S) requests via a proxy. Only HTTP(S) proxy is supported, not SOCKS proxy or anything else.

Configure

The http_proxy, https_proxy, no_proxy environment variables are used to specify proxy settings. The environment variable is not case sensitive.

  • http_proxy: Proxy server to use for HTTP requests.
  • https_proxy: Proxy server to use for HTTPS requests.
  • no_proxy: Comma-separated list of hosts, IP addresses, or IP ranges in CIDR format which should not use the proxy. Synapse will directly connect to these hosts.

The http_proxy and https_proxy environment variables have the form: [scheme://][<username>:<password>@]<host>[:<port>]

  • Supported schemes are http:// and https://. The default scheme is http:// for compatibility reasons; it is recommended to set a scheme. If scheme is set to https:// the connection uses TLS between Synapse and the proxy.

    NOTE: Synapse validates the certificates. If the certificate is not valid, then the connection is dropped.

  • Default port if not given is 1080.

  • Username and password are optional and will be used to authenticate against the proxy.

Examples

NOTE: Synapse does not apply the IP blacklist to connections through the proxy (since the DNS resolution is done by the proxy). It is expected that the proxy or firewall will apply blacklisting of IP addresses.

Connection types

The proxy will be used for:

  • push
  • url previews
  • phone-home stats
  • recaptcha validation
  • CAS auth validation
  • OpenID Connect
  • Outbound federation
  • Federation (checking public key revocation)
  • Fetching public keys of other servers
  • Downloading remote media

It will not be used for:

  • Application Services
  • Identity servers
  • In worker configurations
    • connections between workers
    • connections from workers to Redis

Troubleshooting

If a proxy server is used with TLS (HTTPS) and no connections are established, it is most likely due to the proxy's certificates. To test this, the validation in Synapse can be deactivated.

NOTE: This has an impact on security and is for testing purposes only!

To deactivate the certificate validation, the following setting must be made in homserver.yaml.

use_insecure_ssl_client_just_for_testing_do_not_use: true