Intro

This is a minimal case to demonstrate a bug in Sceptre where values are incorrectly shared between StackGroups.

Issue

Sceptre caches template values between StackGroups, resulting in incorrect rendering.

In the sceptre directory there are two StackGroups for different environments.

In the dev environment in dev/config.yaml a variable env is set. In the ci environment this has been omitted.

Expected behaviour

Trying to generate / launch the ci/simple stack should result in an error.

Actual behaviour

The stack only fails some of the time. Some times it generates with the env value from the dev stack.

Executing

NOTE Sceptre collects it's file list in a set, which are non-deterministic in Python. As such, the following may need to be run a number of times to see the bug.

cd sceptre
sceptre generate ci/simple

Example output

Correct behaviour:

$ sceptre sceptre generate ci/simple
"'env' is undefined"

Incorrect behaviour:

$ sceptre generate ci/simple
---
AWSTemplateFormatVersion: '2010-09-09'
Description: Simple template for testing Sceptre


Resources:
  Type: AWS::SSM::Parameter
  Properties:
    Name: !Sub '/testing/dev'
    Type: String
    Value: "Sceptre env: dev"