Detect Next.js build phase and skip DATABASE_URL check during Docker build

Dockerfile

@@ -11,6 +11,7 @@ WORKDIR /app
 COPY --from=deps /app/node_modules ./node_modules
 COPY . .
 ENV NEXT_TELEMETRY_DISABLED=1
+ENV NEXT_PHASE=phase-production-build
 RUN npm run build
 
 FROM base AS runner

src/lib/db.ts

@@ -1,26 +1,26 @@
 import { Pool } from 'pg';
 
-const connectionString = process.env.DATABASE_URL;
-
 function createPool() {
+  const connectionString = process.env.DATABASE_URL;
+
   if (!connectionString) {
-    if (process.env.NODE_ENV === 'production') {
+    if (typeof process.env.NEXT_PHASE === 'string' && process.env.NEXT_PHASE.includes('phase-production-build')) {
-      throw new Error('DATABASE_URL environment variable is not set');
+      // Next.js collects page data during the build. We don't need a real DB for that.
+      return {
+        query: async () => {
+          throw new Error('DATABASE_URL environment variable is not set');
+        },
+        connect: async () => {
+          throw new Error('DATABASE_URL environment variable is not set');
+        },
+        end: async () => {},
+        on: () => {},
+        removeListener: () => {},
+      } as unknown as Pool;
     }
-    // During build we don't need a real connection; return a stubbed pool
+    throw new Error('DATABASE_URL environment variable is not set');
-    // that throws clearly if someone actually tries to query.
-    return {
-      query: async () => {
-        throw new Error('DATABASE_URL environment variable is not set');
-      },
-      connect: async () => {
-        throw new Error('DATABASE_URL environment variable is not set');
-      },
-      end: async () => {},
-      on: () => {},
-      removeListener: () => {},
-    } as unknown as Pool;
   }
+
   return new Pool({ connectionString });
 }