diff --git a/packages/backend/server/src/base/config/register.ts b/packages/backend/server/src/base/config/register.ts
index 2d183c588d..9d203c5a4d 100644
--- a/packages/backend/server/src/base/config/register.ts
+++ b/packages/backend/server/src/base/config/register.ts
@@ -37,7 +37,7 @@ export type ConfigDescriptor<T> = {
 type ConfigDefineDescriptor<T> = {
   desc: string;
   default: T;
-  validate?: (value: T) => boolean;
+  validate?: (value: T) => z.SafeParseReturnType<T, T>;
   shape?: z.ZodType<T>;
   env?: string | [string, EnvConfigType];
   link?: string;
@@ -158,7 +158,7 @@ function standardizeDescriptor<T>(
     default: desc.default,
     type,
     validate: (value: T) => {
-      return shape.safeParse(value);
+      return desc.validate ? desc.validate(value) : shape.safeParse(value);
     },
     env,
     link: desc.link,
@@ -257,7 +257,15 @@ export function getDefaultConfig(): AppConfigSchema {
       const { success, error } = desc.validate(defaultValue);
 
       if (!success) {
-        throw error;
+        throw new Error(
+          error.issues
+            .map(issue => {
+              return `Invalid config for module [${module}] with key [${key}]
+Value: ${JSON.stringify(defaultValue)}
+Error: ${issue.message}`;
+            })
+            .join('\n')
+        );
       }
 
       set(modulizedConfig, key, defaultValue);
diff --git a/packages/backend/server/src/base/redis/config.ts b/packages/backend/server/src/base/redis/config.ts
index 9fc25a1f33..741fed70c3 100644
--- a/packages/backend/server/src/base/redis/config.ts
+++ b/packages/backend/server/src/base/redis/config.ts
@@ -23,7 +23,7 @@ defineModuleConfig('redis', {
     desc: 'The database index of redis server to be used(Must be less than 10).',
     default: 0,
     env: ['REDIS_SERVER_DATABASE', 'integer'],
-    validate: val => val >= 0 && val < 10,
+    shape: z.number().int().nonnegative().max(10),
   },
   host: {
     desc: 'The host of the redis server.',
diff --git a/packages/backend/server/src/core/config/config.ts b/packages/backend/server/src/core/config/config.ts
index 2a163bf6be..d8457fabce 100644
--- a/packages/backend/server/src/core/config/config.ts
+++ b/packages/backend/server/src/core/config/config.ts
@@ -9,12 +9,12 @@ export interface ServerFlags {
 declare global {
   interface AppConfigSchema {
     server: {
-      externalUrl: string;
+      externalUrl?: string;
       https: boolean;
       host: string;
       port: number;
       path: string;
-      name: string | undefined;
+      name?: string;
     };
     flags: ServerFlags;
   }
@@ -29,9 +29,16 @@ defineModuleConfig('server', {
     desc: `Base url of AFFiNE server, used for generating external urls.
 Default to be \`[server.protocol]://[server.host][:server.port]\` if not specified.
     `,
-    default: 'http://localhost:3010',
+    default: '',
     env: 'AFFINE_SERVER_EXTERNAL_URL',
-    shape: z.string().url(),
+    validate: val => {
+      // allow to be nullable and empty string
+      if (!val) {
+        return { success: true, data: val };
+      }
+
+      return z.string().url().safeParse(val);
+    },
   },
   https: {
     desc: 'Whether the server is hosted on a ssl enabled domain (https://).',