Catch TLSParameterErrors from docker-py

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>

compose/cli/docker_client.py

@@ -5,9 +5,11 @@ import logging
 import os
 
 from docker import Client
+from docker.errors import TLSParameterError
 from docker.utils import kwargs_from_env
 
 from ..const import HTTP_TIMEOUT
+from .errors import UserError
 
 log = logging.getLogger(__name__)
 
@@ -20,8 +22,16 @@ def docker_client(version=None):
     if 'DOCKER_CLIENT_TIMEOUT' in os.environ:
         log.warn('The DOCKER_CLIENT_TIMEOUT environment variable is deprecated. Please use COMPOSE_HTTP_TIMEOUT instead.')
 
-    kwargs = kwargs_from_env(assert_hostname=False)
+    try:
+        kwargs = kwargs_from_env(assert_hostname=False)
+    except TLSParameterError:
+        raise UserError(
+            'TLS configuration is invalid - make sure your DOCKER_TLS_VERIFY and DOCKER_CERT_PATH are set correctly.\n'
+            'You might need to run `eval "$(docker-machine env default)"`')
+
     if version:
         kwargs['version'] = version
+
     kwargs['timeout'] = HTTP_TIMEOUT
+
     return Client(**kwargs)