Heaviside is a domain specific language (DSL) and Python compiler / support libraries for working with AWS StepFunctions.
The reason for a StepFunctions DSL is that the state machine language, while flexible, is hard to write and maintain. The DSL provides a simplied format for writing StepFunction state machines and serveral of common flow control statements.
The StepFunctionDSL document describes the Heaviside DSL.
In this document .hsd
will be used to denote a StepFunction file written in
the Heaviside DSL. The extension .sfn
will be used to denote a StepFunction
file written in the AWS state machine language.
pip install heaviside
The Heaviside package installs a script called heaviside
that provides a CLI
to the library. Running the command without arguments or with the --help
or
-h
flag will provide detailed help.
All sub-commands (except compile
) connect to AWS to manipulate StepFunctions.
There are multiple ways to define the AWS credentials, listed in the order of
precedence.
- Explicitly pass the values as command line arguments or environmental variables
- Pass a file path to a JSON file with the arguments
- Letting Boto3 try to resolve secret / access keys
- Looking at EC2 meta data for current AWS region
- Looking at current IAM user for AWS account_id
The compile
sub-command doesn't connect to AWS, but does use the region and
account_id values when resolving Task ARNs. If the Heaviside DSL file has full
Task ARNs or the compiled file will not be uploaded to AWS these values can be
blank.
Note: Since compile
doesn't connect to AWS, only the first two options in
the list above are valid for passing the region and account_id value.
To compile a Heaviside file into a AWS StepFunction file use the compile
sub-command.
$ heaviside compile state_machine.hsd -o state_machine.sfn
The heaviside
script can compile and upload the resulting file to AWS.
$ heaviside create state_machine.hsd AwsIamStepFunctionRole
Arguments:
state_machine.hsd
: The path to the Step Function definition written in the Heaviside DSL.AwsIamStepFunctionRole
: The AWS IAM Role that the StepFunction will use when executing. Most often this will be used to control which Lambdas and Activities the StepFunction has permission to execute.
The heaviside
script can update an existing Step Function definition and / or
IAM role in AWS.
$ heaviside update state_machine --file state_machine.hsd --role AwsIamStepFunctionRole
Arguments:
state_machine
: Name of the state machine to updatestate_machine.hsd
: The path to the Step Function definition written in the Heaviside DSL.AwsIamStepFunctionRole
: The AWS IAM Role that the StepFunction will use when executing. Most often this will be used to control which Lambdas and Activities the StepFunction has permission to execute.
The delete
sub-command can be used to delete an existing StepFunction
$ heaviside delete state_machine
The start
sub-command can be used to start executing a StepFunction.
$ heaviside start --json "{}" state_machine
Note: By default the start
sub-command will wait until the
execution has finished and will print the output of the StepFunction.
The Heaviside package installs the Python library heaviside
. The public
API is documented in the Library API file.
Currently Heaviside has only been tested with Python 2.7 and 3.5.
- statelint: A Ruby project that verifies a AWS StepFunction definition file. Includes checks like making sure that all states are reachable. Helpful when developing a new StepFunction to ensure everything is correct. It will catch structural problems that Heaviside doesn't check for.
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