"Failed to establish a new connection" Azure App Service

We have a custom Docker image that runs a Tomcat and exposes port 7000 to handle traffic. We store this image in a container registry accessible from our Azure subscription.

We deploy the image using Azure App Service and use the WEBSITES_PORT configuration to bind the port 7000. However, the App Service fails to start with the following error in the App Service logs

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connection.py", line 175, in _new_conn
    (self._dns_host, self.port), self.timeout, **extra_kw
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/util/connection.py", line 96, in create_connection
    raise err
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/util/connection.py", line 86, in create_connection
    sock.connect(sa)
OSError: [Errno 113] No route to host

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 706, in urlopen
    chunked=chunked,
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 382, in _make_request
    self._validate_conn(conn)
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 1010, in _validate_conn
    conn.connect()
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connection.py", line 358, in connect
    conn = self._new_conn()
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connection.py", line 187, in _new_conn
    self, "Failed to establish a new connection: %s" % e
urllib3.exceptions.NewConnectionError: <urllib3.connection.HTTPSConnection object at 0x7ff2e335b358>: Failed to establish a new connection: [Errno 113] No route to host

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib64/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/az/lib/python3.6/site-packages/azure/cli/command_modules/appservice/custom.py", line 2598, in _get_log
    preload_content=False
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/request.py", line 75, in request
    method, url, fields=fields, headers=headers, **urlopen_kw
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/request.py", line 96, in request_encode_url
    return self.urlopen(method, url, **extra_kw)
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/poolmanager.py", line 375, in urlopen
    response = conn.urlopen(method, u.request_uri, **kw)
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 796, in urlopen
    **response_kw
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 796, in urlopen
    **response_kw
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 796, in urlopen
    **response_kw
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 756, in urlopen
    method, url, error=e, _pool=self, _stacktrace=sys.exc_info()[2]
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/util/retry.py", line 574, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='[app-service-name].scm.[ase-name].appserviceenvironment.net', port=443): Max retries exceeded with url: /logstream (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7ff2e335b358>: Failed to establish a new connection: [Errno 113] No route to host',))

My guess is when the App Service starts it pulls some code from the SCM url.

The App Service is deployed in a NSG with ports 80/443 open to both inbound and outbound traffic.