Managing code locations with Definitions

A code location is a collection of Dagster definitions loadable and accessible by Dagster's tools, such as the CLI, UI, and Dagster+. A code location comprises:

• A reference to a Python module that has an instance of Definitions in a top-level variable
• A Python environment that can successfully load that module

Definitions within a code location have a common namespace and must have unique names. This allows them to be grouped and organized by code location in tools.

A single deployment can have one or multiple code locations.

Code locations are loaded in a different process and communicate with Dagster system processes over an RPC mechanism. This architecture provides several advantages:

• When there is an update to user code, the Dagster webserver/UI can pick up the change without a restart.
• You can use multiple code locations to organize jobs, but still work on all of your code locations using a single instance of the webserver/UI.
• The Dagster webserver process can run in a separate Python environment from user code so job dependencies don't need to be installed into the webserver environment.
• Each code location can be sourced from a separate Python environment, so teams can manage their dependencies (or even their Python versions) separately.

Relevant APIs

Name	Description
Definitions	The object that contains all the definitions defined within a code location. Definitions include assets, jobs, resources, schedules, and sensors.

Defining code locations

A Dagster project can be scaffolded using the create-dagster CLI. This will create a top-level variable that contains a Definitions object in a Python module.

Deploying and loading code locations

• Local development
• Dagster+ deployment
• Open source deployment

Local development

Dagster can load a project directly as a code location:

dg dev

This command loads the definitions in the project as a code location in the current Python environment.

Fore more information about local development, including how to configure your local instance, see "Running Dagster locally".

Dagster+ deployment

See the Dagster+ code locations documentation.

Open source deployment

The workspace.yaml file is used to load code locations for open source (OSS) deployments. This file specifies how to load a collection of code locations and is typically used in advanced use cases. For more information, see "workspace.yaml reference".

Troubleshooting

Error	Description and resolution
Cannot have more than one Definitions object defined at module scope	Dagster found multiple Definitions objects in a single Python module. Only one Definitions object may be in a single code location.