Configuration Providers

Configuration Providers in the context of the dlt library refer to different sources from which configuration values and secrets can be retrieved for a data pipeline. These providers form a hierarchy, with each having its own priority in determining the values for function arguments.

The provider hierarchy

If function signature has arguments that may be injected, dlt looks for the argument values in providers.

Providers

1. Environment Variables: At the top of the hierarchy are environment variables. If a value for a specific argument is found in an environment variable, dlt will use it and will not proceed to search in lower-priority providers.

2. Vaults (Airflow/Google/AWS/Azure): These are specialized providers that come after environment variables. They can provide configuration values and secrets. However, they typically focus on handling sensitive information.

3. secrets.toml and config.toml Files: These files are used for storing both configuration values and secrets. secrets.toml is dedicated to sensitive information, while config.toml contains non-sensitive configuration data.

4. Default Argument Values: These are the values specified in the function's signature. They have the lowest priority in the provider hierarchy.

Example

@dlt.source
def google_sheets(
    spreadsheet_id=dlt.config.value,
    tab_names=dlt.config.value,
    credentials=dlt.secrets.value,
    only_strings=False
):
    sheets = build('sheets', 'v4', credentials=Services.from_json(credentials))
    tabs = []
    for tab_name in tab_names:
        data = sheets.get(spreadsheet_id, tab_name).execute().values()
        tabs.append(dlt.resource(data, name=tab_name))
    return tabs

In case of google_sheets() it will look for: spreadsheet_id, tab_names and credentials.

Each provider has its own key naming convention, and dlt is able to translate between them.

The argument name is a key in the lookup.

At the top of the hierarchy are Environment Variables, then secrets.toml and config.toml files. Providers like Airflow/Google/AWS/Azure Vaults will be inserted after the Environment provider but before TOML providers.

For example, if spreadsheet_id is found in environment variable SPREADSHEET_ID, dlt will not look in TOML files and below.

The values passed in the code explicitly are the highest in provider hierarchy. The default values of the arguments have the lowest priority in the provider hierarchy.

info

Explicit Args > ENV Variables > Vaults: Airflow etc. > secrets.toml > config.toml > Default Arg Values

Secrets are handled only by the providers supporting them. Some providers support only secrets (to reduce the number of requests done by dlt when searching sections).

1. secrets.toml and environment may hold both config and secret values.
2. config.toml may hold only config values, no secrets.
3. Various vaults providers hold only secrets, dlt skips them when looking for values that are not secrets.

info

Context-aware providers will activate in the right environments i.e. on Airflow or AWS/GCP VMachines.

Provider key formats

TOML vs. Environment Variables

Providers may use different formats for the keys. dlt will translate the standard format where sections and key names are separated by "." into the provider-specific formats.

1. For TOML, names are case-sensitive and sections are separated with ".".
2. For Environment Variables, all names are capitalized and sections are separated with double underscore "__".

Example: When dlt evaluates the request dlt.secrets["my_section.gcp_credentials"] it must find the private_key for Google credentials. It will look

1. first in env variable MY_SECTION__GCP_CREDENTIALS__PRIVATE_KEY and if not found,
2. in secrets.toml with key my_section.gcp_credentials.private_key.

Environment provider

Looks for the values in the environment variables.

TOML provider

The TOML provider in dlt utilizes two TOML files:

• secrets.toml - This file is intended for storing sensitive information, often referred to as "secrets".
• config.toml - This file is used for storing configuration values.

By default, the .gitignore file in the project prevents secrets.toml from being added to version control and pushed. However, config.toml can be freely added to version control.

info

TOML provider always loads those files from .dlt folder which is looked relative to the current Working Directory.

Example: If your working directory is my_dlt_project and your project has the following structure:

my_dlt_project:
  |
  pipelines/
    |---- .dlt/secrets.toml
    |---- google_sheets.py

and you run python pipelines/google_sheets.py then dlt will look for secrets.toml in my_dlt_project/.dlt/secrets.toml and ignore the existing my_dlt_project/pipelines/.dlt/secrets.toml.

If you change your working directory to pipelines and run python google_sheets.py it will look for my_dlt_project/pipelines/.dlt/secrets.toml as (probably) expected.

caution

It's worth mentioning that the TOML provider also has the capability to read files from ~/.dlt/ (located in the user's home directory) in addition to the local project-specific .dlt folder.