variables.md

Variables

Ringmaster is not a scripting language and only offers the bare minimum to pass values between scripts.

Not all handlers support variable substitution, eg:

• Cloudformation - use parameters instead
• remote_cloudformation.yaml - use parameters instead
• Bash - use environment variables
• Python - use data field

Variable substitution is most useful for things like Kubernetes deployment descriptors/secrets.

Assigning

Variables are assigned on creation:

• In the databag - databag.yaml
• As the output of script

It is not possible to assign variables at the time of evaluation

Resolution

The databag is a simple dict (AKA map, associative array, hash...). The latest assignment replaces any existing one.

At the end of a ringmaster run, all resolved values are saved to output_databag.yaml.

output_databag.yaml will be loaded instead of databag.yaml if it exists

Scope

Databag variables are flat within each stack directory. By creating multiple stacks you can support multiple independent scopes and by copying output_databag.yaml between scopes, you can pass vetoed variables

Naming

• lower-case snake case, eg: my_variable
• variable names are case-sensitive

Interpolation expressions

Interpolation is processed by Jinja2 so behaves as documented. {{ name_of_variable }} identifies a substitution variable. The entire expression will be replaced with the value of name_of_variable during processing

Missing variables

Missing variables will trigger an error advising the name of the missing variable.