Fix Docker networking: use environment variables for Redis connection

The application was hardcoded to connect to localhost:6379, which doesn't work
in Docker Compose where Redis runs in a separate container.

Changes:
- Updated chat.py to read REDIS_HOST and REDIS_PORT from environment variables
  * Defaults to localhost:6379 for local development
  * Can be overridden for Docker or other deployment scenarios
- Updated docker-compose.yml to set REDIS_HOST=redis for container networking
- Replaced deprecated 'links' with 'depends_on' in docker-compose.yml
- Updated README.md with:
  * Modern Python 3.11+ and Redis 7+ requirements
  * Separate sections for local development and Docker Compose usage
  * Documentation of environment variables

This fixes the "Connection refused" error when running via docker-compose.

Author: claude

README.md

@@ -1,24 +1,48 @@
 # redis-streams-fastapi-chat
 A simple demo of Redis Streams backed Chat app using Websockets, Python Asyncio and FastAPI/Starlette.
 
-Requires Python version >= 3.6 and Redis
+Requires Python version >= 3.11 and Redis 7+
 
 # Overview
 This project has been created to help understand some related concepts. Python standard library asyncio, websockets (which are often cited as a classic use case for async python code), also Redis Streams. It is very much inteded to be an intentionally simple starting point rather than a usable product as is.
 
 # Installation
 
+## Local Development
+
 ```shell
 $ pip install -r requirements.txt
 ```
 
+Make sure you have Redis running locally:
+```shell
+$ redis-server
+```
+
 # Usage
 
+## Local Development
+
 ```shell
 $ python chat.py
 ```
 
-# Docker compose
-If you don't have redis installed you can use the docker-compose.yml file to set up a
-working environment. 
+Then open http://localhost:9080 in your browser.
+
+## Docker Compose
+
+The easiest way to run the application with all dependencies:
+
+```shell
+$ docker-compose up
+```
+
+This will start both the chat application and Redis in containers. The app will be available at http://localhost:9080
+
+## Environment Variables
+
+The following environment variables can be configured:
+
+- `REDIS_HOST` - Redis server hostname (default: `localhost`, set to `redis` in Docker)
+- `REDIS_PORT` - Redis server port (default: `6379`) 
 

chat.py

@@ -15,8 +15,8 @@
 from websockets.exceptions import ConnectionClosedError, ConnectionClosedOK
 from redis.exceptions import ConnectionError as ServerConnectionClosedError
 
-REDIS_HOST = 'localhost'
-REDIS_PORT = 6379
+REDIS_HOST = os.getenv('REDIS_HOST', 'localhost')
+REDIS_PORT = int(os.getenv('REDIS_PORT', '6379'))
 XREAD_TIMEOUT = 0
 XREAD_COUNT = 100
 NUM_PREVIOUS = 30

docker-compose.yml

@@ -8,8 +8,11 @@ services:
       - "8082:8082"
     volumes:
       - .:/code
-    links:
-      - "redis"
+    environment:
+      - REDIS_HOST=redis
+      - REDIS_PORT=6379
+    depends_on:
+      - redis
   redis:
     image: "redis:7-alpine"
     ports: