diff --git a/docker-entrypoint.d/30-frontend-config.sh b/docker-entrypoint.d/30-frontend-config.sh
new file mode 100644
index 0000000..747b7dc
--- /dev/null
+++ b/docker-entrypoint.d/30-frontend-config.sh
@@ -0,0 +1,19 @@
+#!/bin/sh
+# Generates runtime frontend config from container environment.
+# Runs automatically at container start via nginx's /docker-entrypoint.d/.
+# Lets one image talk to any backend: set VITE_API_URL on the service
+# (compose environment or .env) and restart — no rebuild needed.
+# The app (src/api/agent.ts) prefers this file, falling back to the
+# build-time VITE_API_URL when it is absent (local dev, vite preview).
+set -eu
+
+CONFIG_FILE="/usr/share/nginx/html/config.js"
+mkdir -p "$(dirname "${CONFIG_FILE}")"
+
+if [ -z "${VITE_API_URL:-}" ]; then
+  echo "frontend-config: VITE_API_URL not set, writing empty config (build-time env applies)"
+  printf 'window.__APP_CONFIG__ = {};\n' > "${CONFIG_FILE}"
+else
+  echo "frontend-config: writing config.js with VITE_API_URL=${VITE_API_URL}"
+  printf 'window.__APP_CONFIG__ = { VITE_API_URL: "%s" };\n' "${VITE_API_URL}" > "${CONFIG_FILE}"
+fi
diff --git a/index.html b/index.html
index 33ec6ce..883cfe9 100644
--- a/index.html
+++ b/index.html
@@ -32,6 +32,9 @@
   <body>
     <noscript>You need to enable JavaScript to run this app.</noscript>
     <div id="root"></div>
+    <!-- Runtime config (backend URL) injected at container start.
+         See docker-entrypoint.d/30-frontend-config.sh and public/config.js. -->
+    <script src="/config.js"></script>
     <script type="module" src="/src/index.tsx"></script>
     <!--
       This HTML file is a template.
diff --git a/public/config.js b/public/config.js
new file mode 100644
index 0000000..dffa4fe
--- /dev/null
+++ b/public/config.js
@@ -0,0 +1,6 @@
+// Placeholder replaced at container start by
+// docker-entrypoint.d/30-frontend-config.sh, which writes the real
+// VITE_API_URL from the container environment. Served as /config.js
+// (see index.html). Empty here so local builds fall back to the
+// build-time import.meta.env value.
+window.__APP_CONFIG__ = {};
diff --git a/src/api/agent.ts b/src/api/agent.ts
index 9e82fd5..62ca8d9 100644
--- a/src/api/agent.ts
+++ b/src/api/agent.ts
@@ -11,7 +11,14 @@ const sleep = (delay: number) => {
         setTimeout(resolve, delay)
     })
 }
-axios.defaults.baseURL = import.meta.env.VITE_API_URL
+// Backend URL: container runtime config first (/config.js, written from
+// VITE_API_URL at container start), build-time env as fallback for dev.
+declare global {
+    interface Window {
+        __APP_CONFIG__?: { VITE_API_URL?: string }
+    }
+}
+axios.defaults.baseURL = window.__APP_CONFIG__?.VITE_API_URL ?? import.meta.env.VITE_API_URL
 
 axios.interceptors.request.use((config) => {
     const token = userToken.get()
