Synapse does not exit on a config failure

[richvdh]

If there is an error during startup (like not being able to load the ssl certs or bind to the http port), Synapse prints out an error but does not exit

[richvdh]

For example, if the cert doesn't exist:

2019-02-01 11:12:19,426 - twisted - 245 - ERROR - - Traceback (most recent call last):
2019-02-01 11:12:19,428 - twisted - 245 - ERROR - -   File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/_base.py", line 111, in check_file
2019-02-01 11:12:19,429 - twisted - 245 - ERROR - -     os.stat(file_path)
2019-02-01 11:12:19,429 - twisted - 245 - ERROR - - FileNotFoundError: [Errno 2] No such file or directory: '/etc/matrix-synapse/homeserver.tls.crt'
2019-02-01 11:12:19,433 - twisted - 245 - ERROR - - 
2019-02-01 11:12:19,433 - twisted - 245 - ERROR - - During handling of the above exception, another exception occurred:
2019-02-01 11:12:19,433 - twisted - 245 - ERROR - - 
2019-02-01 11:12:19,434 - twisted - 245 - ERROR - - Traceback (most recent call last):
2019-02-01 11:12:19,434 - twisted - 245 - ERROR - -   File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/app/homeserver.py", line 430, in start
2019-02-01 11:12:19,434 - twisted - 245 - ERROR - -     hs.config.read_certificate_from_disk()
2019-02-01 11:12:19,434 - twisted - 245 - ERROR - -   File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/tls.py", line 99, in read_certificate_from_disk
2019-02-01 11:12:19,435 - twisted - 245 - ERROR - -     self.tls_certificate = self.read_tls_certificate(self.tls_certificate_file)
2019-02-01 11:12:19,437 - twisted - 245 - ERROR - -   File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/tls.py", line 240, in read_tls_certificate
2019-02-01 11:12:19,438 - twisted - 245 - ERROR - -     cert_pem = self.read_file(cert_path, "tls_certificate")
2019-02-01 11:12:19,440 - twisted - 245 - ERROR - -   File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/_base.py", line 133, in read_file
2019-02-01 11:12:19,442 - twisted - 245 - ERROR - -     cls.check_file(file_path, config_name)
2019-02-01 11:12:19,444 - twisted - 245 - ERROR - -   File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/_base.py", line 115, in check_file
2019-02-01 11:12:19,444 - twisted - 245 - ERROR - -     % (file_path, config_name, e.strerror)
2019-02-01 11:12:19,445 - twisted - 245 - ERROR - - synapse.config._base.ConfigError: Error accessing file '/etc/matrix-synapse/homeserver.tls.crt' (config for tls_certificate): No such file or directory
2019-02-01 11:12:19,475 - twisted - 245 - CRITICAL - - Unhandled error in Deferred:
2019-02-01 11:12:19,475 - twisted - 245 - CRITICAL - - 
Traceback (most recent call last):
  File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/_base.py", line 111, in check_file
    os.stat(file_path)
FileNotFoundError: [Errno 2] No such file or directory: '/etc/matrix-synapse/homeserver.tls.crt'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/app/homeserver.py", line 430, in start
    hs.config.read_certificate_from_disk()
  File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/tls.py", line 99, in read_certificate_from_disk
    self.tls_certificate = self.read_tls_certificate(self.tls_certificate_file)
  File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/tls.py", line 240, in read_tls_certificate
    cert_pem = self.read_file(cert_path, "tls_certificate")
  File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/_base.py", line 133, in read_file
    cls.check_file(file_path, config_name)
  File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/config/_base.py", line 115, in check_file
    % (file_path, config_name, e.strerror)
synapse.config._base.ConfigError: Error accessing file '/etc/matrix-synapse/homeserver.tls.crt' (config for tls_certificate): No such file or directory

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
  File "/opt/venvs/matrix-synapse/lib/python3.5/site-packages/synapse/app/homeserver.py", line 450, in start
    sys.exit(1)
SystemExit: 1

[richvdh]

This was fixed in #4567.

Synapse does now exit, but the experience is still not entirely satisfactory (#4640, #4641).