gen-env Skill

gen-env Skill

Generate or review a gen-env command that enables running multiple isolated instances of a project on localhost simultaneously (e.g., multiple worktrees, feature branches, or versions).

The Problem

Without isolation, multiple instances of the same project:

• Fight for hardcoded ports (3000, 5432, 8080)
• Share Docker volumes → data corruption
• Share browser cookies/localStorage → auth confusion
• Have ambiguous container names → can't tell which is which
• Risk catastrophic cleanup → docker down -v nukes everything

The Solution: Instance Identity

Everything flows from a workspace name:

name = "feature-x"
         ↓
┌─────────────────────────────────────────────────────┐
│ COMPOSE_PROJECT_NAME = localnet-feature-x           │
│ DOCKER_NETWORK       = localnet-feature-x           │
│ VOLUME_PREFIX        = localnet-feature-x           │
│ CONTAINER_PREFIX     = localnet-feature-x-          │
│ TILT_HOST            = feature-x.localhost          │
│ Ports                = dynamically allocated        │
│ URLs                 = derived from host + ports    │
└─────────────────────────────────────────────────────┘

Isolation Dimensions

1. Port Isolation

Each instance gets unique ports from ephemeral range (49152-65535).

2. Data Isolation

Docker Compose project name controls volume naming:

• Instance A: localnet-main_postgres_data
• Instance B: localnet-feature-x_postgres_data