flocker-deploy can return erroneous wrong number of arguments message

[dwgebler]

Due to a bug in the implementation of environment YAML config, flocker-deploy can end up returning an "Error: Wrong number of arguments" message (as a result of twisted.python.usage raising a TypeError with that message), when in fact the correct number of command-line arguments are given.

The real underlying problem is that flocker.node._config assigns the environment attribute of the Characteristic Application model as a dict, which Characteristic then complains is not hashable:

applications[application_name] = Application(
                name=application_name,
                image=image,
                volume=volume,
                ports=frozenset(ports),
                environment=environment)

In this code, environment is either dict or None, so we need to do something like ensuring environment is always a dict (even if empty) and then doing:

applications[application_name] = Application(
                name=application_name,
                image=image,
                volume=volume,
                ports=frozenset(ports),
                environment=frozenset(environment.items()))

This frozenset can later be converted back to a dict and processed as normal.

[wallrj]

Yep, that works. With a slight modification to the GearEnvironment class (below)

The tests and docstrings will probably need updating too.

diff --git a/flocker/node/_config.py b/flocker/node/_config.py
index cab15d7..e8de7d5 100644
--- a/flocker/node/_config.py
+++ b/flocker/node/_config.py
@@ -212,7 +212,7 @@ class Configuration(object):
                 image=image,
                 volume=volume,
                 ports=frozenset(ports),
-                environment=environment)
+                environment=frozenset(environment.items()))

             if config:
                 raise ConfigurationError(
diff --git a/flocker/node/gear.py b/flocker/node/gear.py
index 4a68f86..82da392 100644
--- a/flocker/node/gear.py
+++ b/flocker/node/gear.py
@@ -38,7 +38,7 @@ class GearEnvironment(object):
         the Gear REST API.
         """
         variables = []
-        for k, v in self.variables.items():
+        for k, v in self.variables:
             variables.append(dict(name=k, value=v))
         return dict(id=self.id, variables=variables)

[wallrj]

I think the problem actually occurs when we create a frozenset of the Applications. Which attempts to hash each Application and triggers the hash and the attrs_to_tuple function in characteristic

• https://github.com/hynek/characteristic/blob/master/characteristic.py#L219-L223
• https://github.com/hynek/characteristic/blob/master/characteristic.py#L158-L162

Perhaps we could suggest an improvement to Characteristic for better handling of dicts and other unhashable attributes. Maybe automatically call dict.items for DictType?

[itamarst]

I don't think that's a good idea lacking ability to make stuff read-only. There's a reason dictionaries aren't hashable; if you mutate it and it's a key in a dictionary unexpected things would happen.