Add mention and warning about ACME v1 deprecation to the TLS config

changelog.d/6907.doc

@@ -0,0 +1 @@
+Update Synapse's documentation to warn about the deprecation of ACME v1.

docs/sample_config.yaml

@@ -466,6 +466,11 @@ retention:
 # ACME support: This will configure Synapse to request a valid TLS certificate
 # for your configured `server_name` via Let's Encrypt.
 #
+# Note that ACME v1 is now deprecated, and Synapse currently doesn't support
+# ACME v2. This means that this feature currently won't work with installs set
+# up after November 2019. For more info, and alternative solutions, see
+# https://github.com/matrix-org/synapse/blob/master/docs/ACME.md#deprecation-of-acme-v1
+#
 # Note that provisioning a certificate in this way requires port 80 to be
 # routed to Synapse so that it can complete the http-01 ACME challenge.
 # By default, if you enable ACME support, Synapse will attempt to listen on

synapse/config/tls.py

@@ -32,6 +32,17 @@
 
 logger = logging.getLogger(__name__)
 
+ACME_SUPPORT_ENABLED_WARN = """\
+This server uses Synapse's built-in ACME support. Note that ACME v1 has been
+deprecated by Let's Encrypt, and that Synapse doesn't currently support ACME v2,
+which means that this feature will not work with Synapse installs set up after
+November 2019, and that it may stop working on June 2020 for installs set up
+before that date.
+
+For more info and alternative solutions, see
+https://github.com/matrix-org/synapse/blob/master/docs/ACME.md#deprecation-of-acme-v1
+--------------------------------------------------------------------------------"""
+
 
 class TlsConfig(Config):
     section = "tls"
@@ -44,6 +55,9 @@ def read_config(self, config: dict, config_dir_path: str, **kwargs):
 
         self.acme_enabled = acme_config.get("enabled", False)
 
+        if self.acme_enabled:
+            logger.warning(ACME_SUPPORT_ENABLED_WARN)
+
         # hyperlink complains on py2 if this is not a Unicode
         self.acme_url = six.text_type(
             acme_config.get("url", "https://acme-v01.api.letsencrypt.org/directory")
@@ -362,6 +376,11 @@ def generate_config_section(
         # ACME support: This will configure Synapse to request a valid TLS certificate
         # for your configured `server_name` via Let's Encrypt.
         #
+        # Note that ACME v1 is now deprecated, and Synapse currently doesn't support
+        # ACME v2. This means that this feature currently won't work with installs set
+        # up after November 2019. For more info, and alternative solutions, see
+        # https://github.com/matrix-org/synapse/blob/master/docs/ACME.md#deprecation-of-acme-v1
+        #
         # Note that provisioning a certificate in this way requires port 80 to be
         # routed to Synapse so that it can complete the http-01 ACME challenge.
         # By default, if you enable ACME support, Synapse will attempt to listen on

synapse/handlers/acme.py

@@ -25,6 +25,15 @@
 
 logger = logging.getLogger(__name__)
 
+ACME_REGISTER_FAIL_ERROR = """
+--------------------------------------------------------------------------------
+Failed to register with the ACME provider. This is likely happening because the install
+is new, and ACME v1 has been deprecated by Let's Encrypt and is disabled for installs set
+up after November 2019.
+At the moment, Synapse doesn't support ACME v2. For more info and alternative solution,
+check out https://github.com/matrix-org/synapse/blob/master/docs/ACME.md#deprecation-of-acme-v1
+--------------------------------------------------------------------------------"""
+
 
 class AcmeHandler(object):
     def __init__(self, hs):
@@ -71,7 +80,12 @@ def start_listening(self):
         # want it to control where we save the certificates, we have to reach in
         # and trigger the registration machinery ourselves.
         self._issuer._registered = False
-        yield self._issuer._ensure_registered()
+
+        try:
+            yield self._issuer._ensure_registered()
+        except Exception:
+            logger.error(ACME_REGISTER_FAIL_ERROR)
+            raise
 
     @defer.inlineCallbacks
     def provision_certificate(self):