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| 1 | +# Environment Variable Configuration Pattern |
| 2 | + |
| 3 | +This document describes the pattern for using environment variables to override |
| 4 | +application configuration values. The goal is a **single name** that appears |
| 5 | +identically in the Python config class, the Docker Compose `environment:` |
| 6 | +block, the Azure Container App configuration screen, and any `.env` files. |
| 7 | + |
| 8 | +## Core rule |
| 9 | + |
| 10 | +> **The Python constant name and the environment variable name MUST be |
| 11 | +> identical.** |
| 12 | +
|
| 13 | +When an operator sets `REASONING_EFFORT=medium` on an Azure container, they |
| 14 | +should be able to grep the codebase for that exact string and land on the |
| 15 | +config class attribute that consumes it. No prefix translation, no casing |
| 16 | +changes. |
| 17 | + |
| 18 | +## How to add a new overridable config value |
| 19 | + |
| 20 | +### 1. Add the class attribute with `os.getenv` |
| 21 | + |
| 22 | +```python |
| 23 | +# UMLBot/config/config.py |
| 24 | +class UMLBotConfig: |
| 25 | + # <short comment explaining the setting and valid values> |
| 26 | + MY_NEW_SETTING: str = os.getenv("MY_NEW_SETTING", "default_value") |
| 27 | +``` |
| 28 | + |
| 29 | +- The first argument to `os.getenv` is the **same string** as the attribute name. |
| 30 | +- Always provide a sensible default so the app runs without any env vars set. |
| 31 | +- Use a type annotation on the attribute. |
| 32 | + |
| 33 | +### 2. Add it to `docker-compose.yml` |
| 34 | + |
| 35 | +```yaml |
| 36 | +services: |
| 37 | + umlbot: |
| 38 | + environment: |
| 39 | + MY_NEW_SETTING: ${MY_NEW_SETTING:-default_value} |
| 40 | +``` |
| 41 | +
|
| 42 | +The `${VAR:-default}` syntax lets the host's env override the compose default, |
| 43 | +which in turn overrides the Python default. Use the **same default** in both |
| 44 | +places to avoid surprises. |
| 45 | + |
| 46 | +### 3. Add it to `.env.example` |
| 47 | + |
| 48 | +```bash |
| 49 | +# Description of the setting (default: default_value) |
| 50 | +# MY_NEW_SETTING=default_value |
| 51 | +``` |
| 52 | + |
| 53 | +Keep entries commented out so a bare `cp .env.example .env` produces a |
| 54 | +working configuration that matches the Python defaults. |
| 55 | + |
| 56 | +### 4. Reference it in code |
| 57 | + |
| 58 | +```python |
| 59 | +from UMLBot.config.config import UMLBotConfig |
| 60 | +
|
| 61 | +value = UMLBotConfig.MY_NEW_SETTING |
| 62 | +``` |
| 63 | + |
| 64 | +Never call `os.getenv` a second time elsewhere in the code. All env var |
| 65 | +reads are centralized in the config class. |
| 66 | + |
| 67 | +## Naming conventions |
| 68 | + |
| 69 | +| Scope | Convention | Example | |
| 70 | +|-------|-----------|---------| |
| 71 | +| UMLBot-specific infrastructure | `UMLBOT_` prefix | `UMLBOT_PLANTUML_JAR_PATH` | |
| 72 | +| LLM / API behaviour settings | Descriptive, no prefix | `REASONING_EFFORT` | |
| 73 | +| Cross-service URLs | `UMLBOT_` prefix | `UMLBOT_ENDPOINT` | |
| 74 | + |
| 75 | +The prefix is useful when an env var might collide with another service's |
| 76 | +variable in a shared container group. For settings that are clearly |
| 77 | +domain-specific (like `REASONING_EFFORT` for OpenAI's Responses API), a prefix |
| 78 | +adds noise without reducing ambiguity. |
| 79 | + |
| 80 | +Use your judgement, but when in doubt, match the name the external API or |
| 81 | +documentation already uses. |
| 82 | + |
| 83 | +## Current inventory |
| 84 | + |
| 85 | +| Python constant | Env var | Default | Location | |
| 86 | +|----------------|---------|---------|----------| |
| 87 | +| `UMLBOT_PLANTUML_JAR_PATH` | `UMLBOT_PLANTUML_JAR_PATH` | `/opt/plantuml/plantuml.jar` | `UMLBotConfig` | |
| 88 | +| `UMLBOT_DATA_DIR`* | `UMLBOT_DATA_DIR` | `/data` | `UMLBotConfig` | |
| 89 | +| `REASONING_EFFORT` | `REASONING_EFFORT` | `low` | `UMLBotConfig` | |
| 90 | +| `UMLBOT_ENDPOINT`** | `UMLBOT_ENDPOINT` | `http://localhost:8000` | `streamlit_app.py` | |
| 91 | + |
| 92 | +\* `UMLBOT_DATA_DIR` is consumed as `DATA_DIR` in the config class today. |
| 93 | +This is a legacy inconsistency that should be aligned in a future PR. |
| 94 | + |
| 95 | +\** `UMLBOT_ENDPOINT` lives in `streamlit_app.py` as `API_BASE_URL` rather |
| 96 | +than in `UMLBotConfig`. This is another legacy inconsistency to align. |
| 97 | + |
| 98 | +## Anti-patterns |
| 99 | + |
| 100 | +- **Different names for the same thing.** Don't name the attribute |
| 101 | + `JAR_PATH` and the env var `UMLBOT_PLANTUML_JAR_PATH`. An operator |
| 102 | + reading the Azure config screen should be able to find the code with a |
| 103 | + single search. |
| 104 | + |
| 105 | +- **Scattered `os.getenv` calls.** Every env-var read should be in |
| 106 | + `UMLBotConfig` (or the equivalent config module for other projects). |
| 107 | + Duplicate reads in service code make it hard to audit what the app |
| 108 | + depends on. |
| 109 | + |
| 110 | +- **Missing defaults.** If a setting doesn't have a default, the app crashes |
| 111 | + on startup when the env var is absent. If a value is truly required (like |
| 112 | + an API key), use `manage_sensitive()` instead of `os.getenv`. |
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