diff --git a/.env.example b/.env.example
index ebec073..8c90e1e 100644
--- a/.env.example
+++ b/.env.example
@@ -2,6 +2,8 @@
 DOMAIN=game.example.com
 PUBLIC_SCHEME=https
 ACME_EMAIL=admin@example.com
+# Set http://DOMAIN when an external reverse proxy terminates TLS.
+CADDY_SITE_ADDRESS=
 HTTP_PORT=80
 HTTPS_PORT=443
 
diff --git a/README.md b/README.md
index 00b497a..9a14694 100644
--- a/README.md
+++ b/README.md
@@ -23,6 +23,12 @@ DNS의 `DOMAIN` A/AAAA record가 호스트를 가리키고 80/443 TCP 및 443 UD
 Core2026 clone, frozen-lockfile install, build와 Gateway migration 때문에 수 분이
 걸릴 수 있습니다.
 
+외부 reverse proxy가 TLS를 종료하고 이 stack의 HTTP port로 전달한다면
+`PUBLIC_SCHEME=https`, `CADDY_SITE_ADDRESS=http://DOMAIN`을 함께 설정합니다.
+예를 들어 host `14999`로 전달할 때는 `HTTP_PORT=14999`로 두고, 사용하지 않는
+`HTTPS_PORT`는 충돌하지 않는 별도 host port로 지정합니다. 외부 proxy는 원래
+`Host` header를 보존해야 합니다.
+
 runtime은 기본적으로 memory/swap 각각 4 GiB, CPU 4개, PID 256개 상한을
 가집니다. 호스트 용량에 맞춰 `RUNTIME_*_LIMIT`을 조정할 수 있지만 0 또는
 무제한으로 두지 않습니다. PM2 process/restart 수가 예상보다 증가하면 로그 수집보다
diff --git a/compose.yaml b/compose.yaml
index 95e3ee0..3f529e4 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -121,7 +121,7 @@ services:
     image: caddy:2.10.2-alpine
     environment:
       DOMAIN: ${DOMAIN:?set DOMAIN in .env}
-      SITE_ADDRESS: ${DOMAIN:?set DOMAIN in .env}
+      SITE_ADDRESS: ${CADDY_SITE_ADDRESS:-${DOMAIN:?set DOMAIN in .env}}
       ACME_EMAIL: ${ACME_EMAIL:?set ACME_EMAIL in .env}
     ports:
       - ${HTTP_PORT:-80}:80
diff --git a/runtime/validate-env.mjs b/runtime/validate-env.mjs
index 2257256..0d3482f 100644
--- a/runtime/validate-env.mjs
+++ b/runtime/validate-env.mjs
@@ -52,6 +52,18 @@ export const validateEnvironment = (env) => {
     errors.push('DOMAIN must be a hostname without a scheme, path, or port');
   }
 
+  const caddySiteAddress = env.CADDY_SITE_ADDRESS?.trim() ?? '';
+  if (caddySiteAddress) {
+    try {
+      const parsed = new URL(caddySiteAddress);
+      if (!['http:', 'https:'].includes(parsed.protocol) || parsed.hostname !== domain || parsed.pathname !== '/') {
+        errors.push('CADDY_SITE_ADDRESS must be http://DOMAIN or https://DOMAIN');
+      }
+    } catch {
+      errors.push('CADDY_SITE_ADDRESS must be http://DOMAIN or https://DOMAIN');
+    }
+  }
+
   const email = env.ACME_EMAIL?.trim() ?? '';
   if (email && !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email)) errors.push('ACME_EMAIL must be a valid email address');
 
diff --git a/test/validate-env.test.mjs b/test/validate-env.test.mjs
index 06e0f9c..614b913 100644
--- a/test/validate-env.test.mjs
+++ b/test/validate-env.test.mjs
@@ -20,6 +20,18 @@ test('accepts a complete public repository environment', () => {
   assert.deepEqual(validateEnvironment(validEnv), []);
 });
 
+test('accepts an HTTP Caddy address for external TLS termination', () => {
+  assert.deepEqual(
+    validateEnvironment({ ...validEnv, CADDY_SITE_ADDRESS: 'http://game.test.invalid' }),
+    [],
+  );
+});
+
+test('rejects a Caddy address for a different host', () => {
+  const errors = validateEnvironment({ ...validEnv, CADDY_SITE_ADDRESS: 'http://other.test.invalid' });
+  assert.ok(errors.some((error) => error.includes('CADDY_SITE_ADDRESS')));
+});
+
 test('accepts paired HTTPS credentials without embedding them in the URL', () => {
   assert.deepEqual(
     validateEnvironment({ ...validEnv, CORE_REPOSITORY_USERNAME: 'deploy', CORE_REPOSITORY_TOKEN: 'token' }),