diff --git a/deployment/docker/.env.example b/deployment/docker/.env.example
index 1277f8e..2512e0e 100644
--- a/deployment/docker/.env.example
+++ b/deployment/docker/.env.example
@@ -1,3 +1,5 @@
+## Docker-internal service URLs (do not use 127.0.0.1/localhost here).
+## Containers must reach each other via Compose service names.
 NATS_URL=nats://nats:4222
 CLICKHOUSE_URL=http://clickhouse:8123
 CLICKHOUSE_DATABASE=default