[gordonmurray]

Bringing this 2023 experiment up to date with Doris 4.0.8, the release labelled Stable by Apache Doris, and Kafka 4.1.2.

The default setup now runs one frontend, one backend and Kafka. A separate Compose configuration keeps the three-frontend, three-backend experiment available with its own persistent volumes and three table replicas.

• Replace the old alpha images with pinned releases and add readiness checks.
• Provision Kafka, create the topic and Routine Load job, and load repeatable sample data.
• Correct connection ports, network addresses, startup dependencies and configuration handling.
• Replace hardcoded host storage paths with named volumes and document preservation and reset commands.
• Resume the demo's paused ingestion job after services restart, retaining its Kafka offsets.
• Add a smoke test for fresh Kafka ingestion and Actions checks for configuration, scripts and persistence.

Validation: GitHub Actions passes Compose validation for both configurations, Bash syntax, ShellCheck, fresh Kafka ingestion, and data persistence plus fresh ingestion after recreating containers. The larger cluster is configuration-checked; its runtime smoke test needs a machine with enough memory.

This creates a fresh demo. It does not migrate existing 2.0-alpha data.