[Resolve #390] Cast all parameters to strings

[matrinox]

Problem

Sceptre allows you to pass non-string values as parameters. Boto3 only allows string parameters. Refer to #390 for more details.

Example config:

parameters:
  Port: 3000
  RuleNumber: 500
  LoggingEnabled: True

Solution

To solve this, all non-string values are coerced into strings. An exception is made for booleans (True/False becomes "true"/"false"). List values are now recursively formatted. This has the side effect of supporting nested array values for parameters (no tests for this).

Alternatives

1. Create boto3 PR to support non-string parameters for CloudFormation create/update stack APIs. This is also a possibility but it doesn't hurt to cast the values to strings here as well.
2. Raise exception when passing non-string values. This is slightly better than current – more descriptive error messages – but personally, it isn't as good as the proposed solution. Development time is roughly the same.
3. Do nothing or add this to readme. This is definitely the simplest and least riskiest solution but the UX is weaker than point Load only external hook classes required by relevant stack config(s) #2.

[JuanCanham]

Why do we want to downcase this?

[matrinox]

If your parameter is defined like this:

Parameters:
  Key:
    Type: String
    AllowedValues:
      - False
      - True

Only "false"/"true" will work, not "False"/"True". Same goes for False/True. So you need to downcase it.

[JuanCanham]

Makes sense

[JuanCanham]

@ngfgrant who is authorised to approve this it looks good to me though

[matrinox]

@ngfgrant Can you look into this PR please?

[ngfgrant]

Hey @matrinox - yeh this is definitely on my list. I am aiming to get a v1 release out this week and then will look at this as potentially something for v2 release. It is definitely on my list though ;)

[matrinox]

Awesome, thanks for the update!

[ngfgrant]

@matrinox I am going to get another couple of PRs in relating to refactoring the way config is handled and then after I am done would it be ok if I ask you to update this from master? There is not big changes, mainly that the methods on stack have moved from that object so your code just needs pasted elsewhere 😄

[matrinox]

@ngfgrant When you finish doing that, please mention again and I will get to it :).

[stig]

Any chance of this being picked up? Numbers / booleans in the stack config file not being coerced to strings and this causing failure is the most frequent cause of git commit --fixup at our shop!

[alex-harvey-z3q]

Any chance of this or similar being merged? This has been a big pain point for my team.

[matrinox]

@alexharv074 we already migrated to terraform so I'm not interested in updating this branch any longer. Sorry :(

You're welcome to take the code and run with it though, I don't mind.

[zaro0508]

I have proposed an alternative idea to help with this in #925