diff --git a/.env.example b/.env.example
new file mode 100644
index 0000000..3cbc7a3
--- /dev/null
+++ b/.env.example
@@ -0,0 +1,14 @@
+# optional, used for fetching build logs, not configured automatically
+RAILWAY_TOKEN=your_railway_token_here
+
+# optional but automatically configured by Railway
+# RAILWAY_PROJECT_ID=your_project_id_here
+# RAILWAY_SERVICE_ID=your_service_id_here
+# RAILWAY_ENVIRONMENT_ID=your_environment_id_here
+# RAILWAY_DEPLOYMENT_ID=your_deployment_id_here
+
+# optional, automatically configured by Railway
+# PORT=5800
+
+# optional, has a default you may not want
+# RAILWAY_PUBLIC_DOMAIN=your-domain.railway.app
diff --git a/Dockerfile b/Dockerfile
index 51f59eb..9e4e52e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -51,5 +51,10 @@ COPY --from=builder-demo /build/demo/target/x86_64-pc-windows-gnu/release/demo.e
 COPY --from=builder-demo /build/demo/target/x86_64-unknown-linux-gnu/release/demo ./demo-linux
 COPY --from=builder-server /build/server/target/release/dynamic-preauth ./dynamic-preauth
 
-EXPOSE 5800
+# Build-time arg for PORT, default to 5800
+ARG PORT=5800
+# Runtime environment var for PORT, default to build-time arg
+ENV PORT=${PORT}
+EXPOSE ${PORT}
+
 CMD ["/app/dynamic-preauth"]
\ No newline at end of file