Don't create server contexts when TLS is disabled

we aren't going to use them anyway.

changelog.d/4617.misc

@@ -0,0 +1 @@
+Don't create server contexts when TLS is disabled

synapse/app/_base.py

@@ -214,6 +214,11 @@ def refresh_certificate(hs):
     disk and updating the TLS context factories to use them.
     """
     hs.config.read_certificate_from_disk()
+
+    if hs.config.no_tls:
+        # nothing else to do here
+        return
+
     hs.tls_server_context_factory = context_factory.ServerContextFactory(hs.config)
 
     if hs._listening_services:

synapse/crypto/context_factory.py

@@ -43,8 +43,6 @@ class ServerContextFactory(ContextFactory):
             logger.exception("Failed to enable elliptic curve for TLS")
         context.set_options(SSL.OP_NO_SSLv2 | SSL.OP_NO_SSLv3)
         context.use_certificate_chain_file(config.tls_certificate_file)
-
-        if not config.no_tls:
         context.use_privatekey(config.tls_private_key)
 
         # https://hynek.me/articles/hardening-your-web-servers-ssl-ciphers/