Merge pull request #362 from kooba/env_var_configs

Basic support for environment variables.

docs/cli.rst

@@ -44,6 +44,31 @@ and providing a simple YAML configuration file:
 The ``LOGGING`` entry is passed to :func:`logging.config.dictConfig` and should conform to the schema for that call.
 
 
+Environment variable substitution
+---------------------------------
+YAML configuration files have basic support for environment variables.
+You can use bash style syntax: ``${ENV_VAR}``
+Optionally you can provide default values ``${ENV_VAR:default_value}``
+
+
+.. code-block:: yaml
+
+    # foobar.yaml
+    AMQP_URI: amqp://${RABBITMQ_USER:guest}:${RABBITMQ_PASSWORD:password}@${RABBITMQ_HOST:localhost}
+
+To run your service and set environment variables for it to use:
+
+.. code-block:: shell
+
+    $ RABBITMQ_USER=user RABBITMQ_PASSWORD=password RABBITMQ_HOST=host nameko run --config ./foobar.yaml <module>[:<ServiceClass>]
+
+If you need to quote the values in your YAML file, the explicit ``!env_var`` resolver is required:
+
+.. code-block:: yaml
+
+    # foobar.yaml
+    AMQP_URI: !env_var "amqp://${RABBITMQ_USER:guest}:${RABBITMQ_PASSWORD:password}@${RABBITMQ_HOST:localhost}"
+
 Interacting with running services
 ---------------------------------
 

nameko/cli/main.py

@@ -1,10 +1,31 @@
 from __future__ import print_function
 
 import argparse
+import os
+import re
+import yaml
 
 from nameko.exceptions import CommandError, ConfigurationError
 from . import backdoor, run, shell
 
+ENV_VAR_MATCHER = re.compile(
+    r"""
+        \$\{       # match characters `${` literally
+        ([^}:\s]+) # 1st group: matches any character except `}` or `:`
+        :?         # matches the literal `:` character zero or one times
+        ([^}]+)?   # 2nd group: matches any character except `}`
+        \}         # match character `}` literally
+    """, re.VERBOSE
+)
+IMPLICIT_ENV_VAR_MATCHER = re.compile(
+    r"""
+        .*          # matches any number of any characters
+        \$\{.*\}    # matches any number of any characters
+                    # between `${` and `}` literally
+        .*          # matches any number of any characters
+    """, re.VERBOSE
+)
+
 
 def setup_parser():
     parser = argparse.ArgumentParser()
@@ -19,9 +40,25 @@ def setup_parser():
     return parser
 
 
+def _replace_env_var(match):
+    env_var, default = match.groups()
+    return os.environ.get(env_var, default)
+
+
+def _env_var_constructor(loader, node):
+    value = loader.construct_scalar(node)
+    return ENV_VAR_MATCHER.sub(_replace_env_var, value)
+
+
+def setup_yaml_parser():
+    yaml.add_constructor('!env_var', _env_var_constructor)
+    yaml.add_implicit_resolver('!env_var', IMPLICIT_ENV_VAR_MATCHER)
+
+
 def main():
     parser = setup_parser()
     args = parser.parse_args()
+    setup_yaml_parser()
     try:
         args.main(args)
     except (CommandError, ConfigurationError) as exc:

test/cli/test_main.py

@@ -1,9 +1,11 @@
 import sys
 
 from mock import patch
+import os
 import pytest
+import yaml
 
-from nameko.cli.main import main, setup_parser
+from nameko.cli.main import main, setup_parser, setup_yaml_parser
 from nameko.exceptions import CommandError, ConfigurationError
 
 
@@ -52,3 +54,48 @@ def test_flag_action(param, value):
         args.append(param)
     parsed = parser.parse_args(args)
     assert parsed.rlwrap is value
+
+
+class TestConfigEnvironmentVariables(object):
+
+    @pytest.mark.parametrize(('yaml_config', 'env_vars', 'expected_config'), [
+        # no default value, no env value
+        ('FOO: ${BAR}', {}, {'FOO': ''}),
+        # use default value if env value not provided
+        ('FOO: ${BAR:foo}', {}, {'FOO': 'foo'}),
+        # use env value
+        ('FOO: ${BAR}', {'BAR': 'bar'}, {'FOO': 'bar'}),
+        # use env value instead of default
+        ('FOO: ${BAR:foo}', {'BAR': 'bar'}, {'FOO': 'bar'}),
+        # handles multi line
+        (
+            """
+            FOO: ${BAR:foo}
+            BAR: ${FOO:bar}
+            """,
+            {'BAR': 'bar', 'FOO': 'foo'},
+            {'FOO': 'bar', 'BAR': 'foo'}
+        ),
+        # quoted values don't work without explicit resolver
+        ('FOO: "${BAR:foo}"', {'BAR': 'bar'}, {'FOO': '${BAR:foo}'}),
+        # quoted values work only with explicit resolver
+        ('FOO: !env_var "${BAR:foo}"', {'BAR': 'bar'}, {'FOO': 'bar'}),
+        # $ sign can be used
+        ('FOO: $bar', {}, {'FOO': '$bar'}),
+        # multiple substitutions
+        (
+            'FOO: http://${BAR:foo}/${FOO:bar}',
+            {'BAR': 'bar', 'FOO': 'foo'},
+            {'FOO': 'http://bar/foo'}),
+    ])
+    def test_environment_vars_in_config(
+        self, yaml_config, env_vars, expected_config
+    ):
+        setup_yaml_parser()
+
+        with patch.dict('os.environ'):
+            for key, val in env_vars.items():
+                os.environ[key] = val
+
+            results = yaml.load(yaml_config)
+            assert results == expected_config