Skip to content
Testaroo
yaml1.1 KB

Docker Compose Anchors and x- Extension Fields

Compose with three x- extension fields carrying YAML anchors that are merged into services. The trap is ordering: a tool that strips x- keys before parsing the YAML destroys the anchors and the file stops resolving.

Config parsingEncoding detectionEditor testing
Preview, first 45 linesyaml
# Compose with x- extension fields and YAML anchors. Both are load-bearing here: `x-` keys are
# ignored by Compose but are ordinary YAML, and the anchors under them are merged into services
# by the YAML loader before Compose ever sees the document. A tool that strips x- keys BEFORE
# parsing YAML destroys the anchors and the file stops resolving.
x-logging: &default-logging
  driver: json-file
  options:
    max-size: 10m
    max-file: "3"

x-common: &common
  restart: unless-stopped
  logging: *default-logging
  networks:
    - backend
  environment:
    TZ: Etc/UTC

x-healthcheck-defaults: &healthcheck-defaults
  interval: 10s
  timeout: 2s
  retries: 3

services:
  api:
    <<: *common
    image: registry.example.invalid/example-org/orders:1.4.0
    ports:
      - "8080:8080"
    healthcheck:
      <<: *healthcheck-defaults
      test: ["CMD", "example-healthcheck"]

  worker:
    <<: *common
    image: registry.example.invalid/example-org/worker:1.4.0
    command: ["worker", "--queue", "orders"]
    healthcheck:
      <<: *healthcheck-defaults
      retries: 10

networks:
  backend:
    driver: bridge

Specifications

Anchors
3
Merge Keys
4
Extension Fields
3
Services
2
Edge Case
stripping x- keys before YAML parsing destroys the anchors

Testing contract

Expected to pass
Scenario
Resolve a Compose file whose service definitions come from anchors declared under x- keys
Expected result
Both services inherit restart, logging and networks from the merged anchors, and worker's local retries value of 10 overrides the merged default of 3

What is a .yaml file?

YAML (YAML Ain't Markup Language) is a human-readable data-serialization format using indentation, key-value pairs, and lists, and is a superset of JSON. It supports comments, anchors, and multiple documents per file, favoring readability for configuration. Its indentation sensitivity makes it error-prone to hand-edit.

How to use this file

Use an example YAML file to test config parsers, indentation and anchor handling, multi-document streams, and safe-loading to avoid arbitrary object construction.

How to use this file for testing

“Docker Compose Anchors and x- Extension Fields” is a deterministic Testaroo fixture for Config parsing, Encoding detection, Editor testing. TOML and INI configuration files with nested sections and typed values, for testing config parsers and loaders.

Documented properties for this file: YAML · 1,125 bytes. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.

Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such, expect parsers to fail loudly rather than silently accept them.

Pipeline and infrastructure fixtures are inert configuration: steps reference fictional images and scripts, and nothing here executes. Run your linter, schema validator, migrator, or policy engine against them, and expect the deprecated-syntax and intentionally invalid variants to be rejected.

Point your config loader at the file and assert it reads the documented sections and typed values, including any deliberately-tricky nesting or comments.

Code examples

import yaml  # pip install pyyaml

with open("compose-anchors-extensions.yaml") as f:
    data = yaml.safe_load(f)
print(data)

Generated by generation/pipelines.py. Free for any use, no attribution required, license.

Related files