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 bedev/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 beaccount-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 knows
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.