docker-compose: Improve documentation of configuration options.

Also mention LOADBALANCER_IPS in a comment, since we've had a number
of folks tripped up by not discovering it.

Fixes #449.

README.md

@@ -190,10 +190,10 @@ putting it in `/opt/docker/zulip/zulip/certs/` (by default, the
 `zulip` container startup script will generate a self-signed certificate and
 install it in that directory).
 
-**Load balancer**. To tell Zulip that it is behind a load balancer,
-you must set `LOADBALANCER_IPS` to a comma-separated list of IPs or
-CIDR ranges. This will tell Zulip to pass the real IP of the client,
-instead of the IP of the load balancer itself, by [setting the
+**Reverse proxies**. To tell Zulip that it is behind a reverse proxy
+or load balancer, you must set `LOADBALANCER_IPS` to a comma-separated
+list of IPs or CIDR ranges. This will tell Zulip to pass the real IP
+of the client, instead of the IP of the proxy itself, by [setting the
 IPs][loadbalancer-ips] under `[loadbalancer]` in `zulip.conf`.
 
 Your proxy must provide both `X-Forwarded-For` and

docker-compose.yml

@@ -63,6 +63,9 @@ services:
       - "80:80"
       - "443:443"
     environment:
+      # See https://github.com/zulip/docker-zulip#configuration for
+      # details on this section and how to discover the many
+      # additional settings that are supported here.
       DB_HOST: "database"
       DB_HOST_PORT: "5432"
       DB_USER: "zulip"
@@ -90,6 +93,10 @@ services:
       # Uncomment this when configuring the mobile push notifications service
       # SETTING_ZULIP_SERVICE_PUSH_NOTIFICATIONS: "True"
       # SETTING_ZULIP_SERVICE_SUBMIT_USAGE_STATISTICS: "True"
+
+      # If you're using a reverse proxy, you'll want to provide the
+      # comma-separated set of IP addresses to trust here.
+      # LOADBALANCER_IPS: "",
     volumes:
       - "zulip:/data:rw"
     ulimits: