Load configuration values from environment

Configuration values can be loaded from the system environment by adding
a "TUTOR_" prefix.

Environment values supersede values from the user configuration file, so
that we can set values from the command line with "KEY=VAL tutor config
save --silent" even when KEY is already present in the user
configuration file.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Latest
 
+- [Feature] Load configuration parameters from the system environment
 - [Improvement] Automatic environment re-generation after re-configuration
 - [Improvement] Error and interrupt handling in UI and web UI
 - [Bugfix] Fix missing webui env directory

docs/configuration.rst

@@ -15,10 +15,16 @@ Alternatively, you can set each parameter from the command line::
 
     tutor config save --silent --set PARAM1=VALUE1 --set PARAM2=VALUE2
 
-Once the base configuration is created or updated, the environment is automatically re-generated. The environment is the set of all files required to manage an Open edX platform: Dockerfile, ``lms.env.json``, settings files... You can view the environment files in the ``env`` folder::
+Or from the system environment::
+
+    export TUTOR_PARAM1=VALUE1
+
+Once the base configuration is created or updated, the environment is automatically re-generated. The environment is the set of all files required to manage an Open edX platform: Dockerfile, ``lms.env.json``, settings files, etc. You can view the environment files in the ``env`` folder::
 
     ls $(tutor config printroot)/env
 
+With an up-to-date environment, Tutor is ready to launch an Open edX platform and perform usual operations. Below, we document some of the configuration parameters.
+
 .. _docker_images:
 
 ``DOCKER_IMAGE_*`` Custom Docker images

tutor/config.py

@@ -8,6 +8,7 @@ from . import exceptions
 from . import env
 from . import fmt
 from . import opts
+from . import utils
 from .__about__ import __version__
 
 
@@ -24,7 +25,7 @@ def config():
 @opts.key_value
 def save(root, silent, set_):
     config = {}
-    load_files(config, root)
+    load_current(config, root)
     for k, v in set_:
         config[k] = v
     if not silent:
@@ -47,7 +48,7 @@ def load(root):
     exist.
     """
     config = {}
-    load_files(config, root)
+    load_current(config, root)
 
     should_update_env = False
     if not os.path.exists(config_path(root)):
@@ -72,15 +73,29 @@ def load(root):
 
     return config
 
-def load_files(config, root):
+def load_current(config, root):
     convert_json2yml(root)
+    load_base(config, root)
+    load_user(config, root)
+    load_env(config, root)
 
-    # Load base values
-    base = yaml.load(env.read("config.yml"))
+def load_base(config, root):
+    base = yaml.load(env.read("config-base.yml"))
     for k, v in base.items():
         config[k] = v
 
-    # Load user file
+def load_env(config, root):
+    base_config = yaml.load(env.read("config-base.yml"))
+    default_config = yaml.load(env.read("config-defaults.yml"))
+    keys = set(list(base_config.keys()) + list(default_config.keys()))
+
+    for k in keys:
+        env_var = "TUTOR_" + k
+        if env_var in os.environ:
+            print(k, os.environ[env_var])
+            config[k] = utils.parse_yaml_value(os.environ[env_var])
+
+def load_user(config, root):
     path = config_path(root)
     if os.path.exists(path):
         with open(path) as fi:

tutor/opts.py

@@ -1,6 +1,9 @@
 import appdirs
 import click
 
+from . import utils
+
+
 root = click.option(
     "-r", "--root",
     envvar="TUTOR_ROOT",
@@ -31,11 +34,7 @@ class YamlParamType(click.ParamType):
             k, v = value.split("=")
         except ValueError:
             self.fail("'{}' is not of the form 'key=value'.".format(value), param, ctx)
-        if v.isdigit():
-            v = int(v)
-        elif v in ["true", "false"]:
-            v = (v == "true")
-        return (k, v)
+        return k, utils.parse_yaml_value(v)
 
 key_value = click.option(
     "-s", "--set", "set_", type=YamlParamType(), multiple=True, metavar="KEY=VAL",

tutor/utils.py

@@ -11,6 +11,16 @@ from . import fmt
 def random_string(length):
     return "".join([random.choice(string.ascii_letters + string.digits) for _ in range(length)])
 
+def parse_yaml_value(v):
+    """
+    Parse a yaml-formatted string
+    """
+    if v.isdigit():
+        v = int(v)
+    elif v in ["true", "false"]:
+        v = (v == "true")
+    return v
+
 def docker_run(*command):
     return docker("run", "--rm", "-it", *command)