Using environment variables and secrets#

Environment variables, which are key-value pairs configured outside your source code, allow you to dynamically modify application behavior depending on environment.

Using environment variables, you can define various configuration options for your Dagster application and securely set up secrets. For example, instead of hard-coding database credentials - which is bad practice and cumbersome for development - you can use environment variables to supply user details. This allows you to parameterize your pipeline without modifying code or insecurely storing sensitive data.

Declaring environment variables#

How environment variables are declared depends on whether you're developing locally or have already deployed your Dagster project.

# .env

DATABASE_NAME=staging
DATABASE_SCHEMA=sales
DATABASE_USERNAME=salesteam
DATABASE_PASSWORD=supersecretstagingpassword

Accessing environment variables#

In this section, we'll demonstrate how to access environment variables once they've been declared. There are two ways to do this:

• In Python code, which isn't specific to Dagster
• From Dagster configuration, which incorporates environment variables into the Dagster config system

In Python code#

To access environment variables in your Dagster code, you can use os.getenv:

import os

database_name = os.getenv("DATABASE_NAME")

This approach also works for accessing built-in environment variables for Dagster Cloud:

import os

deployment_name = os.getenv("DAGSTER_CLOUD_DEPLOYMENT_NAME")

Refer to the Dagster Cloud Branch Deployments example for a real-world example.

From Dagster configuration#

Configurable Dagster objects - such as ops, assets, resources, I/O managers, and so on - can accept configuration from environment variables. Dagster provides a native way to specify environment variables in your configuration. These environment variables are retrieved at launch time, rather than on initialization as with os.getenv.

This approach has a few unique benefits:

• It provides greater observability. You can see which configuration values are sourced from environment variables in the UI.
• It ensures secret values are hidden in the launchpad, resources UI, and other places where configuration is displayed.
• It makes testing easier, since you can provide string values directly to configuration rather than environment variables.

In Python code#

To access an environment variable as part of a Dagster configuration in Python code, you may use the following special syntax:

"PARAMETER_NAME": EnvVar("ENVIRONMENT_VARIABLE_NAME")

For example:

"access_token": EnvVar("GITHUB_ACCESS_TOKEN")

In YAML or config dictionaries#

To access an environment variable as part of a Dagster configuration in YAML or in a config dictionary, use the following syntax:

"PARAMETER_NAME": {"env": "ENVIRONMENT_VARIABLE_NAME"}

For example:

"access_token": {"env": "GITHUB_ACCESS_TOKEN"}

Refer to the Handling secrets section and Per-environment configuration example for examples.

Handling secrets#

Using environment variables to provide secrets ensures sensitive info won't be visible in your code or the launchpad in the UI. In Dagster, best practice for handling secrets uses configuration and resources.

A resource is typically used to connect to an external service or system, such as a database. Resources can be configured separately from the rest of your app, allowing you to define it once and reuse it as needed.

Let's take a look at an example from the Dagster Crash Course, which creates a GitHub resource and supplies it to assets. Let's start by looking at the resource:

## resources.py

from dagster import StringSource, resource
from github import Github

class GithubClientResource(ConfigurableResource):
  access_token: str

  def get_client(self) -> Github:
    return Github(self.access_token)

Let's review what's happening here:

• This code creates a GitHub resource named GithubClientResource
• By subclassing ConfigurableResource and specifying the access_token field, we're telling Dagster that we want to be able to configure the resource with an access_token parameter
• Since access_token is a string value, this config parameter can either be:
  • An environment variable, or
  • Provided directly in the configuration

As storing secrets in configuration is bad practice, we'll opt for using an environment variable. In this code, we're configuring the resource supplying it to our assets:

# __init__.py

from my_dagster_project import assets
from my_dagster_project.resources import GithubClientResource

from dagster import Definitions, EnvVar, load_assets_from_package_module

defs = Definitions(
    assets=load_assets_from_package_module(assets),
    resources={
        "github_api": GithubClientResource(access_token=EnvVar("GITHUB_ACCESS_TOKEN"))
    },
)

Let's review what's happening here:

• We pass configuration info to the resource when we construct it. In this example, we're telling Dagster to load the access_token from the GITHUB_ACCESS_TOKEN environment variable by wrapping it in EnvVar.
• We're adding that resource to our Definitions object so it's available for our assets.

Parameterizing pipeline behavior#

Using environment variables, you define how your code should execute at runtime.

• Per-environment configuration
• Dagster Cloud Branch Deployments

Example 1: Per-environment configuration#

In this example, we'll demonstrate how to use different I/O manager configurations for local and production environments using configuration (specifically the configured API) and resources.

This example is adapted from the Transitioning data pipelines from development to production guide:

# __init__.py

resources = {
    "local": {
        "snowflake_io_manager": SnowflakePandasIOManager(
            account="abc1234.us-east-1",
            user=EnvVar("DEV_SNOWFLAKE_USER"),
            password=EnvVar("DEV_SNOWFLAKE_PASSWORD"),
            database="LOCAL",
            schema=EnvVar("DEV_SNOWFLAKE_SCHEMA"),
        ),
    },
    "production": {
        "snowflake_io_manager": SnowflakePandasIOManager(
            account="abc1234.us-east-1",
            user="system@company.com",
            password=EnvVar("SYSTEM_SNOWFLAKE_PASSWORD"),
            database="PRODUCTION",
            schema="HACKER_NEWS",
        ),
    },
}

deployment_name = os.getenv("DAGSTER_DEPLOYMENT", "local")

defs = Definitions(
    assets=[items, comments, stories], resources=resources[deployment_name]
)

Let's review what's happening here:

• We've created a dictionary of resource definitions, resources, named after our local and production environments. In this example, we're using a Pandas Snowflake I/O manager.
• For both local and production, we constructed the I/O manager using environment-specific run configuration. Note the differences in configuration between local and production, specifically where environment variables were used.
• Following the resources dictionary, we define the deployment_name variable, which determines the current executing environment. This variable defaults to local, ensuring that DAGSTER_DEPLOYMENT=PRODUCTION must be set to use the production configuration.

Example 2: Dagster Cloud Branch Deployments#

Adapted from the Testing against production with Dagster Cloud Branch Deployments guide, this example demonstrates how to determine the current deployment type at runtime - Branch Deployment or full deployment - without using resources or configuration.

Let's look at a function that determines the current deployment using the DAGSTER_CLOUD_IS_BRANCH_DEPLOYMENT environment variable:

def get_current_env():
  is_branch_depl = os.getenv("DAGSTER_CLOUD_IS_BRANCH_DEPLOYMENT") == "1"
  assert is_branch_depl != None  # env var must be set
  return "branch" if is_branch_depl else "prod"

This function checks the value of DAGSTER_CLOUD_IS_BRANCH_DEPLOYMENT and, if equal to 1, returns a variable with the value of branch. This indicates that the current deployment is a Branch Deployment. Otherwise, the deployment is a full deployment and is_branch_depl will be returned with a value of prod.

Using this info, we can write code that executes differently when in a Branch Deployment or a full deployment.

Troubleshooting#