ADR-0003 Browser runs and screenshots in a Docker container

Metadata

Key	Value
ID	ADR-0003
CrossReference	BC-001, MIL-002, MIL-003

Version History

Date	Status	Author	Reviewer	Change	Commit
2026-10-28	Accepted	Jens Tirsvad Nielsen	AI as stand-in for S02	Initial version	50e8331

Allowed Status values: Proposed, Accepted, Rejected, Deprecated, Superseded by ADR-NNNN.

Context

The bot drives a real browser and every lecture step needs a screenshot. The framework forbids testing a GUI on the host desktop because it takes the user's mouse and keyboard (framework/process/gui-testing.md). Options:

Run Chrome on the host desktop.
Run headless Chromium in a Docker container (Linux).
Run in Windows Sandbox.

Decision

Option 2. A Dockerfile builds an image with Python, Chromium and its driver; the bot takes a headless option, so the same code runs on the host for users who want it. The practice site keeps its data in the browser profile, so a container run keeps the chrome_profile folder in a Docker volume.

Consequences

Positive:

No interference with the user's desktop; reproducible runs for S02.
Screenshots are made the same way each time.

Negative:

Docker is needed for the real-browser runs and screenshots (unit tests need no Docker).
The image download is large.

Affected Artifacts

BC-001 — risk of non-reproducible runs
MIL-002 — builds the image
MIL-003 — first container run

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