Principle:Apache Airflow Configuration Resolution

Knowledge Sources	Apache_Airflow Airflow Docs
Domains	Configuration, Core_Infrastructure
Last Updated	2026-02-08 21:00 GMT

Overview

Hierarchical configuration resolution from multiple sources with defined precedence, enabling configuration via files, environment variables, commands, and secrets backends with predictable override behavior.

Description

Airflow's configuration system resolves values from multiple sources with a strict priority ordering. When a configuration value is requested, the system checks each source in priority order and returns the first non-empty result. This design allows operators to:

• Set sensible defaults in the code itself
• Override defaults via the airflow.cfg configuration file
• Inject secrets from external backends (Vault, AWS SSM) without storing them in files
• Execute shell commands to dynamically compute values (e.g., fetching from metadata services)
• Use environment variables for container-based and CI/CD deployments, which override all file-based sources

This layered approach means a single Airflow installation can be configured differently across environments (development, staging, production) without modifying the configuration file, simply by adjusting environment variables or secrets backend entries.

Usage

This principle governs the resolution of every Airflow configuration value at runtime. It is relevant when:

• Setting up Airflow for the first time
• Moving between deployment environments
• Integrating with external secrets management systems
• Debugging unexpected configuration behavior
• Writing custom operators or plugins that read Airflow configuration

Theoretical Basis

Source Priority Ordering (Highest to Lowest):

Priority	Source	Format	Example
1 (highest)	Environment variables	AIRFLOW__{SECTION}__{KEY} (double underscores)	AIRFLOW__CORE__EXECUTOR=LocalExecutor
2	Command execution	{key}_cmd option in config file	sql_alchemy_conn_cmd = /usr/bin/fetch_db_conn
3	Secrets backend	Configured via [secrets] section	HashiCorp Vault, AWS SSM, GCP Secret Manager
4	Configuration file	airflow.cfg (INI format)	[core] section with executor = LocalExecutor
5 (lowest)	Built-in defaults	Hardcoded in Airflow source	Default values defined in configuration schema

Environment Variable Convention:

Environment variables follow the pattern AIRFLOW__{SECTION}__{KEY} where double underscores separate the section and key. For example:

• AIRFLOW__CORE__EXECUTOR maps to [core] executor
• AIRFLOW__DATABASE__SQL_ALCHEMY_CONN maps to [database] sql_alchemy_conn
• AIRFLOW__WEBSERVER__SECRET_KEY maps to [webserver] secret_key

Type Coercion:

Raw configuration values are strings. The configuration parser applies type coercion based on the expected type of each option:

Target Type	Coercion Rule	Example
bool	Case-insensitive: true/1/yes/on become True; false/0/no/off become False	"True" -> True
int	Standard integer parsing	"8080" -> 8080
float	Standard float parsing	"0.5" -> 0.5
json	json.loads() for complex structures	'{"key": "value"}' -> dict
timedelta	Parses duration strings	"30s", "5m", "2h"
enum	Matches against allowed enum values	"SequentialExecutor"
import path	Imports the specified Python object	"my_module.MyClass" -> class object

Command Execution:

For options that support the _cmd suffix, Airflow executes the specified shell command and uses its stdout as the configuration value. This enables dynamic secret retrieval without a full secrets backend:

[database]
sql_alchemy_conn_cmd = /usr/local/bin/fetch_db_credentials.sh

The command is executed once at startup and the result is cached for the process lifetime.

Secrets Backend Integration:

When a secrets backend is configured, the configuration parser queries it for values before falling back to the config file. This is particularly useful for sensitive values like database credentials and API keys:

[secrets]
backend = airflow.providers.hashicorp.secrets.vault.VaultBackend
backend_kwargs = {"connections_path": "airflow/connections", "variables_path": "airflow/variables"}

Related Pages

Implemented By

• Implementation:Apache_Airflow_Configuration_Parser