Forward arbitrary environment variables over SSH

CONTRIBUTING.md

@@ -64,7 +64,7 @@ requests_).
  - Prasanna Challuri
  - David Matthews
  - Tim Whitcomb
- - (Scott Wales)
+ - Scott Wales
  - Tomek Trzeciak
  - Thomas Coleman
  - Bruno Kinoshita

changes.d/5709.feat.md

@@ -0,0 +1 @@
+Forward arbitrary environment variables over SSH connections

cylc/flow/cfgspec/globalcfg.py

@@ -1416,6 +1416,13 @@ def default_for(
                    {REPLACES}``global.rc[hosts][<host>]copyable
                    environment variables``.
             ''')
+            Conf('ssh forward environment variables', VDR.V_STRING_LIST, '',
+                 desc='''
+                A list containing the names of the environment variables to
+                forward with SSH connections to the server and run hosts
+
+                .. versionchanged:: 8.3.0
+            ''')
             Conf('retrieve job logs', VDR.V_BOOLEAN,
                  desc=f'''
                 {LOG_RETR_SETTINGS['retrieve job logs']}

cylc/flow/remote.py

@@ -298,7 +298,8 @@ def construct_ssh_cmd(
         'CYLC_CONF_PATH',
         'CYLC_COVERAGE',
         'CLIENT_COMMS_METH',
-        'CYLC_ENV_NAME'
+        'CYLC_ENV_NAME',
+        *platform['ssh forward environment variables'],
     ]:
         if envvar in os.environ:
             command.append(

tests/unit/test_remote.py

@@ -15,7 +15,9 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 """Test the cylc.flow.remote module."""
 
-from cylc.flow.remote import run_cmd, construct_rsync_over_ssh_cmd
+from cylc.flow.remote import run_cmd, construct_rsync_over_ssh_cmd, construct_ssh_cmd
+from unittest import mock
+import cylc.flow
 
 
 def test_run_cmd_stdin_str():
@@ -86,3 +88,28 @@ def test_construct_rsync_over_ssh_cmd():
         '/foo/',
         'miklegard:/bar/',
     ]
+
+
+def test_construct_ssh_cmd_forward_env():
+    """ Test for 'ssh forward environment variables'
+    """
+    import os
+
+    host = 'example.com'
+    config = {
+        'ssh command': 'ssh',
+        'use login shell': None,
+        'cylc path': None,
+        'ssh forward environment variables': ['FOO'],
+        }
+
+    # Variable isn't set, no change to command
+    expect = ['ssh', host, 'env', f'CYLC_VERSION={cylc.flow.__version__}', 'cylc', 'play']
+    cmd = construct_ssh_cmd(['play'], config, host)
+    assert cmd == expect
+
+    # Variable is set, appears in `env` list
+    with mock.patch.dict(os.environ, {'FOO': 'BAR'}):
+        expect = ['ssh', host, 'env', f'CYLC_VERSION={cylc.flow.__version__}', 'FOO=BAR', 'cylc', 'play']
+        cmd = construct_ssh_cmd(['play'], config, host)
+        assert cmd == expect