Add an IP bind param to the entrypoint (#447)

* Add an IP bind param to the entrypoint

* Add an example usage to readme

* Rename to BIND

README.md

@@ -262,6 +262,7 @@ These are the environment variables which can be specified at container run time
 | GENERATE_NEW_SAVE | Generate a new save if one does not exist before starting the server  | false | 0.17+ |
 | LOAD_LATEST_SAVE | Load latest when true. Otherwise load SAVE_NAME | true | 0.17+ |
 | PORT | UDP port the server listens on | 34197 | 0.15+ |
+| BIND | IP address (v4 or v6) the server listens on (IP\[:PORT]) | | 0.15+ |
 | RCON_PORT | TCP port the rcon server listens on | 27015 | 0.15+ |
 | SAVE_NAME | Name to use for the save file | _autosave1 | 0.17+ |
 | TOKEN | factorio.com token | | 0.17+ |
@@ -383,6 +384,21 @@ For LAN games the VM needs an internal IP in order for clients to connect. One w
 
 If you're looking for a simple way to deploy this to the Amazon Web Services Cloud, check out the [Factorio Server Deployment (CloudFormation) repository](https://github.com/m-chandler/factorio-spot-pricing). This repository contains a CloudFormation template that will get you up and running in AWS in a matter of minutes. Optionally it uses Spot Pricing so the server is very cheap, and you can easily turn it off when not in use.
 
+## Using a reverse proxy
+
+If you need to use a reverse proxy you can use the following nginx snippet:
+
+```
+stream {
+  server {
+      listen 34197 udp reuseport;
+      proxy_pass my.upstream.host:34197;
+  }
+}
+```
+
+If your factorio host uses multiple IP addresses (very common with IPv6), you might additionally need to bind Factorio to a single IP (otherwise the UDP proxy might get confused with IP mismatches). To do that pass the `BIND` envvar to the container: `docker run --network=host -e BIND=2a02:1234::5678 ...`
+
 ## Troubleshooting
 
 ### My server is listed in the server browser, but nobody can connect

docker/docker-compose.yml

@@ -20,3 +20,4 @@ services:
 #      - USERNAME=FactorioUsername
 #      - TOKEN=FactorioToken
 #      - PORT=34198
+#      - ADDR=::1

docker/files/docker-entrypoint.sh

@@ -5,6 +5,7 @@ FACTORIO_VOL=/factorio
 LOAD_LATEST_SAVE="${LOAD_LATEST_SAVE:-true}"
 GENERATE_NEW_SAVE="${GENERATE_NEW_SAVE:-false}"
 SAVE_NAME="${SAVE_NAME:-""}"
+BIND="${BIND:-""}"
 
 mkdir -p "$FACTORIO_VOL"
 mkdir -p "$SAVES"
@@ -88,6 +89,10 @@ FLAGS=(\
   --server-id /factorio/config/server-id.json \
 )
 
+if [ -n "$BIND" ]; then
+  FLAGS+=( --bind "$BIND" )
+fi
+
 if [[ $LOAD_LATEST_SAVE == true ]]; then
     FLAGS+=( --start-server-load-latest )
 else