Schema: Advanced Features

This page covers advanced schema features for fine-grained control over your configuration.

Immutable Fields

The immutable block lets you define a list of keys that, once set by an early-loading source, cannot be overwritten by a later source. This is useful for protecting critical, foundational values.

schema.yml

immutable:
  - "service.name"
  - "database.port"

Scenario:

1. 01-base.json sets database.port to 5432.
2. 02-prod.yml attempts to set database.port to 9999.

Because database.port is immutable, the overwrite from 02-prod.yml will be ignored, and the final value will remain 5432.

DANGER

This rule is very strict and applies to all sources, including KONFIGO_KEY_ environment variables.

Output Schema Filtering

The outputSchema block allows you to define a "mask" or "template" for your final output. Konfigo will produce a final configuration that only contains the keys present in your output schema file, discarding everything else.

This is useful for creating a clean, public-facing configuration from a larger, internal one that may contain secrets or intermediate values.

schema.yml

outputSchema:
  path: "./public-config-shape.json"

public-config-shape.json

{
  "service": {
    "name": "",
    "url": ""
  },
  "features": {
    "new_ui": false
  }
}

The final output from Konfigo will only contain the service and features blocks.