Sceptre: Variable is undefined

[fabiodouek]

When defining the same variable in the config.yaml in different levels, causes Sceptre to intermittently return an error: is undefined.
Usually if I run again it works, but sometimes I have to run a few times. This is in the scope of creating a changeset.

e.g of structure
-config

• dev
  
  
  
  • config.yaml (variable : x: a)
  
  
  • appb
    
    
    
    
    
    • config.yaml (variable : x: b)
    
    
    
  
  

The error is happening in Sceptre 2.1.0 and 2.1.5 (I havent' tested other versions, but I don't see this issue reported nor fixed in 2.2.0).

[marcoswerneckie]

This problem has often occurred continuously, and rerun has been the only immediate solution but sometimes it is necessary to rerun many times until it works.

[fabiodouek]

The issue was due to variables referenced in a config.yaml from a top-level config.yaml. I understand that this feature is not supported in Sceptre (which would be a useful feature), but somehow in 30% of the cases was working. I removed those references for now, and the problem got resolved.

[ngfgrant]

Is the issue to make the documentation clearer about this specific issue?

[carterdanko]

We have also run into this same issue trying to specify certain variables in the config.yaml for a particular region, but then in some stack_configs lower in the directory either updating vars or adding new vars.

│   config.yaml
│
└───aws_service
│   │   stack_config.yaml

Where in this case we may define vars in the config.yaml as

central_vars:
  key1: true
  key2: false

And in stack_config.yaml, we may need to update or add to that base vars

stack_name: stack-name
template_path: path/to/template
{% set _ = central_vars.update({"key2" : "dummy_value"}) %}
sceptre_user_data:
  input_vars: {{ central_vars }}

[nathan-williams-rozettatechnology]

I think this is related to #937

When rendering config files, Sceptre caches values across stack groups.
The "undefined" you are getting is the correct response, when it "works" it is actually using a value from one of your other config files.

The inconsistency between runs comes from Sceptre using a set to process the config files.
(Sets are non-deterministic in Python).