diff --git a/nextstep-backend/src/models/comments_model.ts b/nextstep-backend/src/models/comments_model.ts
index c5b2d6f..1b0749e 100644
--- a/nextstep-backend/src/models/comments_model.ts
+++ b/nextstep-backend/src/models/comments_model.ts
@@ -30,12 +30,12 @@ const commentSchema: Schema = new mongoose.Schema({
 commentSchema.set('toJSON', {
     transform: (doc: Document, ret: Record<string, any>) => {
         return {
-            id: ret._id,
-            postId: ret.postId,
-            content: ret.content,
-            owner: ret.owner,
-            createdAt: ret.createdAt,
-            updatedAt: ret.updatedAt,
+            id: ret._id.toString(),
+            postId: ret.postId.toString(),
+            content: ret.content as string,
+            owner: ret.owner.toString(),
+            createdAt: ret.createdAt ? ret.createdAt.toISOString() : undefined,
+            updatedAt: ret.updatedAt ? ret.updatedAt.toISOString() : undefined,
         };
     }
 });
diff --git a/nextstep-backend/src/models/company_model.ts b/nextstep-backend/src/models/company_model.ts
index 3abcd2e..b709b4c 100644
--- a/nextstep-backend/src/models/company_model.ts
+++ b/nextstep-backend/src/models/company_model.ts
@@ -46,10 +46,10 @@ const companySchema: Schema = new mongoose.Schema({
 companySchema.set('toJSON', {
     transform: (doc: Document, ret: Record<string, any>) => {
         return {
-            id: ret._id,
-            company: ret.company,
-            company_he: ret.company_he,
-            tags: ret.tags,
+            id: ret._id.toString(),
+            company: ret.company as string,
+            company_he: ret.company_he as string,
+            tags: ret.tags as string[],
             quizzes: ret.quizzes,
         }
     }
diff --git a/nextstep-backend/src/models/posts_model.ts b/nextstep-backend/src/models/posts_model.ts
index ef959be..c8a797a 100644
--- a/nextstep-backend/src/models/posts_model.ts
+++ b/nextstep-backend/src/models/posts_model.ts
@@ -25,13 +25,12 @@ const postSchema: Schema = new mongoose.Schema({
 postSchema.set('toJSON', {
     transform: (doc: Document, ret: Record<string, any>): PostData => {
         return {
-            id: ret._id,
+            id: ret._id.toString(),
             title: ret.title,
             content: ret.content,
             owner: ret.owner._id.toString(),
-            createdAt: ret.createdAt,
-            updatedAt: ret.updatedAt
-
+            createdAt: ret.createdAt ? ret.createdAt.toISOString() : undefined,
+            updatedAt: ret.updatedAt ? ret.updatedAt.toISOString() : undefined
         };
     }
 });
diff --git a/nextstep-backend/src/models/user_model.ts b/nextstep-backend/src/models/user_model.ts
index 62c232e..46dd15a 100644
--- a/nextstep-backend/src/models/user_model.ts
+++ b/nextstep-backend/src/models/user_model.ts
@@ -29,15 +29,15 @@ const userSchema: Schema = new Schema({
 }, { timestamps: true, strict: true, versionKey: false });
 
 userSchema.set('toJSON', {
-    transform: (doc, ret): UserData => {
+    transform: (doc: mongoose.Document, ret: Record<string, any>): UserData => {
         return {
-            id: ret._id,
-            username: ret.username,
-            email: ret.email,
-            password: ret.password,
-            imageFilename: ret?.imageFilename,
-            createdAt: ret.createdAt,
-            updatedAt: ret.updatedAt
+            id: ret._id.toString(),
+            username: ret.username as string,
+            email: ret.email as string,
+            password: ret.password as string,
+            imageFilename: ret?.imageFilename as string | undefined,
+            createdAt: ret.createdAt ? ret.createdAt.toISOString() : undefined,
+            updatedAt: ret.updatedAt ? ret.updatedAt.toISOString() : undefined
         };
     }
 });
diff --git a/nextstep-frontend/.env.template b/nextstep-frontend/.env.template
index 373be25..59afee2 100644
--- a/nextstep-frontend/.env.template
+++ b/nextstep-frontend/.env.template
@@ -2,6 +2,8 @@
 
 VITE_PORT=<VITE_PORT>
 VITE_BACKEND_URL=<VITE_BACKEND_URL>
+VITE_DOMAIN_NAME=<VITE_DOMAIN_NAME>
+VITE_ALLOWED_HOSTS=<demo1.example.com;demo2.example.com;demo3.example.com>
 VITE_REACT_APP_FIREBASE_API_KEY=<VITE_REACT_APP_FIREBASE_API_KEY>
 VITE_REACT_APP_FIREBASE_AUTH_DOMAIN=<VITE_REACT_APP_FIREBASE_AUTH_DOMAIN>
 VITE_REACT_APP_FIREBASE_PROJECT_ID=<VITE_REACT_APP_FIREBASE_PROJECT_ID>
diff --git a/nextstep-frontend/vite.config.ts b/nextstep-frontend/vite.config.ts
index f68a9da..c82bfd8 100644
--- a/nextstep-frontend/vite.config.ts
+++ b/nextstep-frontend/vite.config.ts
@@ -1,15 +1,24 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
-import dotenv from 'dotenv';
+import dotenv from 'dotenv'
 
+dotenv.config()
 
-dotenv.config();
+const allowedHosts = (process.env.VITE_ALLOWED_HOSTS || '')
+  .split(';')
+  .map(host => host.trim())
+  .filter(Boolean) // remove empty strings
 
 // https://vite.dev/config/
 export default defineConfig({
   plugins: [react()],
   server: {
-    port: parseInt(process.env.VITE_PORT || '5000')
+    port: parseInt(process.env.VITE_PORT || '5000'),
+    host: process.env.VITE_DOMAIN_NAME || 'localhost',
+    allowedHosts: allowedHosts.length > 0 ? allowedHosts : undefined
   },
-  preview: { port: parseInt(process.env.VITE_PORT || '5000') }
+  preview: {
+    port: parseInt(process.env.VITE_PORT || '5000'),
+    host: process.env.VITE_DOMAIN_NAME || 'localhost'
+  }
 })