Redis MCP: ECONNREFUSED the loopback address:6379 from Docker (point REDIS_HOST correctly)

TL;DR: connection refused from a containerized Redis MCP server usually means it is trying to reach Redis at the loopback address, which inside the container is itself. Set REDIS_HOST to the real address: host.YOUR_HOST for Redis on your laptop, or the container/service name on a shared Docker network.

Error: connect ECONNREFUSED the loopback address:6379

Fix it

1. Figure out where Redis actually lives relative to the MCP server:

   • Redis on your laptop, MCP server in Docker: host is host.YOUR_HOST.
   • Both in Docker Compose: host is the service name, e.g. redis.
   • Both on the host: the loopback address is correct, check Redis is running.
2. Set it explicitly. Do not rely on the default:

REDIS_HOST=host.YOUR_HOST
REDIS_PORT=6379

In a client config env block, add "REDIS_HOST": "host.YOUR_HOST".

3. Verify from inside the same network namespace if you can:

docker run --rm redis:7 redis-cli -h host.YOUR_HOST ping

Expected: PONG.

4. Restart the MCP server.

   Expected: connection refused is gone.

When to use this

• redis-cli ping works on your host but the MCP server gets ECONNREFUSED.
• The MCP server runs in Docker and Redis runs elsewhere.

When NOT to use this

• Both run on the same host outside Docker and it still refuses. Then Redis is not running or not listening on 6379.
• The error is NOAUTH or WRONGPASS. The connection works; auth is the problem.

Compatibility

• redis/mcp-redis in Docker / Docker Compose.
• Docker Desktop (macOS/Windows) supports host.YOUR_HOST. On Linux, add --add-host=host.YOUR_HOST:host-gateway.

Why it happens

Every container has its own loopback interface. the loopback address inside the MCP container never leaves the container, so it can only reach a Redis running in that same container. The default REDIS_HOST=the loopback address is only correct when server and Redis share a network namespace.

Edge cases

• --network=host on Linux makes container YOURHOST equal host YOURHOST, but it does not work on Docker Desktop for Mac/Windows.
• If Redis is bound to the loopback address in its own config, other containers cannot reach it even by service name. Bind Redis to the all-interfaces address (with a password) for container networking.
• Port mappings (-p 6379:6379) matter for host-to-container, not container-to-container. On a shared network, use the container port directly.

The redis/mcp-redis server defaults REDISHOST to the loopback address and REDISPORT to 6379 (documented in zskbot/catalog image/redis-mcp/guides.md, upstream https://github.com/redis/mcp-redis). When the MCP server runs in Docker and Redis runs on the host (or in another container), the loopback address resolves to the MCP container itself and the connection is refused. The documented pattern in containerized MCP setups is using host.YOUR_HOST as the hostname to reach the host from inside a container, as shown in dockerized MCP server guides.