Terminology

The following terms will be used through the rest of the Sceptre documentation:

Sceptre Project:

The directory which stores the top level config directory.

  • Command Path The Stack or StackGroup that you want to execute a Sceptre command against. For example, if you want to launch vpc.yaml in the example below the command path would be dev/vpc.yaml.

    .
    └── config
        └── dev
            ├── config.yaml
            └── vpc.yaml
    

    Where as if you wanted to delete account-1 in the example below the command path would be account-1.

    .
    └── config
        └── account-1
            └── dev
                └── eu-west-1
                    ├── config.yaml
                    └── vpc.yaml
    

Sceptre Context

Unless you go looking in the code, or you use Sceptre as a python module, you won’t need to worry about SceptreContext.

SceptreContext is a place where we hold information that is relevant to the project, including references to the project paths such as the path to your Sceptre project, templates path, config path, and the default names for your configuration files.

If you are adding functionality to the CLI or you want to use Sceptre as a module you will need to create a SceptreContext and pass it an absolute path to your Sceptre project directory and the “command_path” - the path you are going to execute commands on.

Sceptre Plan

As with SceptreContext you shouldn’t need to interact with SceptrePlan most of the time.

A SceptrePlan takes a SceptreContext and constructs everything you will need to execute a command against your project. After creating a SceptrePlan you will be able to call all available methods for your stacks and access the results from each stack. For example,

plan = SceptrePlan(context)

responses = plan.launch()

## SceptrePlanExecutor

You won’t be able to interact with the SceptrePlanExecutor directly but this part of the code is responsible for taking a SceptrePlan and ensuring all commands on every stack, are executed in the correct order, concurrently. The executor algorithm focuses on correctness over maximal concurrency. It know what to execute and when based on a StackGraph which is created when a SceptrePlan is created.

StackGraph

A StackGraph is a Directed Acyclic Graph where the nodes hold Stack objects and the edges represent a “depends on” relationship. The graph is created when a SceptrePlan is instantiated and is then used during the execution phase to ensure that stack dependency relationships are complete and correct. Previously, in v1 stack dependencies were available between Environments and even within Environments they could be temperamental, this concept resolves this issue.

StackActions

The StackActions class takes a Stack object and uses the data held on the Stack when calling AWS. StackActions is used by the SceptrePlanExecutor. To add new functionality you can add a method to StackActions and it will become available to all Stacks in Sceptre.