diff --git a/package.json b/package.json
index 485e95a4e..5c0390786 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,7 @@
         "lint": "eslint packages --ext ts --fix",
         "pub": "node build/publish",
         "jest": "node build/jest",
-        "start": "node_modules/.bin/hydrooj"
+        "start": "node --async-stack-traces --trace-deprecation --enable-source-maps node_modules/.bin/hydrooj"
     },
     "version": "1.0.0",
     "license": "AGPL-3.0-only",
diff --git a/packages/hydrooj/TODO b/packages/hydrooj/TODO
index c448fc491..e3efbb589 100644
--- a/packages/hydrooj/TODO
+++ b/packages/hydrooj/TODO
@@ -3,5 +3,4 @@
 SETTINGS_PRIVACY.allowRegisteredUsers
 model.setting.ui.name
 pdoc.secretConfig?
-message.markAsRead
-domain_join_application
\ No newline at end of file
+message.markAsRead
\ No newline at end of file
diff --git a/packages/hydrooj/locales/zh_CN.yaml b/packages/hydrooj/locales/zh_CN.yaml
index 0df07cb59..8690bb40e 100644
--- a/packages/hydrooj/locales/zh_CN.yaml
+++ b/packages/hydrooj/locales/zh_CN.yaml
@@ -237,6 +237,7 @@ Domain ID: 域 ID
 domain_dashboard: 管理域
 domain_discussion: 讨论节点
 domain_edit: 编辑域资料
+domain_join_applications: 加域申请
 domain_join: 加入域
 domain_main: 首页
 domain_permission: 管理权限
@@ -408,7 +409,6 @@ Lucky: 手气不错
 manage_dashboard: 控制面板
 manage_join_applications: 加域申请
 manage_module: 管理模块
-manage_script: 脚本管理
 manage_setting: 系统设置
 manage: 管理
 Manage: 管理
diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 87cd17cac..1fdca7824 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.12.6",
+    "version": "2.12.7",
     "bin": "bin/hydrooj.js",
     "main": "dist/loader.js",
     "typings": "dist/loader.d.ts",
diff --git a/packages/hydrooj/src/entry/master.ts b/packages/hydrooj/src/entry/master.ts
index cb29ebff2..950c42738 100644
--- a/packages/hydrooj/src/entry/master.ts
+++ b/packages/hydrooj/src/entry/master.ts
@@ -13,11 +13,15 @@ const lockfile = path.resolve(tmpdir, 'lock.json');
 
 export async function load(call: Entry) {
     if (fs.existsSync(lockfile) && !argv.ignorelock) {
-        const file = require(lockfile);
-        const plist = await pslist();
-        if (file.pid && plist.map((i) => i.pid).includes(file.pid)) {
-            console.error(`Lockfile exists, pid=${file.pid}`);
-            process.exit(1);
+        try {
+            const file = require(lockfile);
+            const plist = await pslist();
+            if (file.pid && plist.map((i) => i.pid).includes(file.pid)) {
+                console.error(`Lockfile exists, pid=${file.pid}`);
+                process.exit(1);
+            }
+        } catch {
+            // Invalid lockfile. ignore.
         }
     }
     const context = {
diff --git a/packages/hydrooj/src/error.ts b/packages/hydrooj/src/error.ts
index cccb4ae3f..01d82c9f7 100644
--- a/packages/hydrooj/src/error.ts
+++ b/packages/hydrooj/src/error.ts
@@ -84,6 +84,9 @@ export const HomeworkNotLiveError = Err('HomeworkNotLiveError', ForbiddenError,
 export const HomeworkNotAttendedError = Err('HomeworkNotAttendedError', ForbiddenError, "You haven't claimed this homework yet.");
 export const RoleAlreadyExistError = Err('RoleAlreadyExistError', ForbiddenError, 'This role already exists.');
 export const CsrfTokenError = Err('CsrfTokenError', ForbiddenError, 'CsrfTokenError');
+export const DomainJoinForbiddenError = Err('DomainJoinForbiddenError', ForbiddenError, 'You are not allowed to join the domain. The link is either invalid or expired.');
+export const DomainJoinAlreadyMemberError = Err('DomainJoinAlreadyMemberError', ForbiddenError, 'Failed to join the domain. You are already a member.');
+export const InvalidJoinInvitationCodeError = Err('InvalidJoinInvitationCodeError', ForbiddenError, 'The invitation code you provided is invalid.');
 
 export const UserNotFoundError = Err('UserNotFoundError', NotFoundError, 'User {0} not found.');
 export const NoProblemError = Err('NoProblemError', NotFoundError, 'No problem.');
@@ -132,6 +135,9 @@ global.Hydro.error = {
     ContestNotLiveError,
     ContestScoreboardHiddenError,
     ContestAlreadyAttendedError,
+    DomainJoinAlreadyMemberError,
+    DomainJoinForbiddenError,
+    InvalidJoinInvitationCodeError,
     UserFacingError,
     SystemError,
     TrainingAlreadyEnrollError,
diff --git a/packages/hydrooj/src/handler/contest.ts b/packages/hydrooj/src/handler/contest.ts
index 27fd08ee9..4fc132a78 100644
--- a/packages/hydrooj/src/handler/contest.ts
+++ b/packages/hydrooj/src/handler/contest.ts
@@ -24,7 +24,7 @@ const ContestHandler = contest.ContestHandlerMixin(Handler);
 
 class ContestListHandler extends ContestHandler {
     @param('rule', Types.String, true)
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, rule = '', page = 1) {
         this.response.template = 'contest_main.html';
         let tdocs;
@@ -55,7 +55,7 @@ class ContestListHandler extends ContestHandler {
 
 class ContestDetailHandler extends ContestHandler {
     @param('tid', Types.ObjectID)
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, tid: ObjectID, page = 1) {
         const tdoc = await contest.get(domainId, tid);
         this.response.template = 'contest_detail.html';
diff --git a/packages/hydrooj/src/handler/discussion.ts b/packages/hydrooj/src/handler/discussion.ts
index 055d5d4b9..ca871eea9 100644
--- a/packages/hydrooj/src/handler/discussion.ts
+++ b/packages/hydrooj/src/handler/discussion.ts
@@ -71,7 +71,7 @@ class DiscussionHandler extends Handler {
 }
 
 class DiscussionMainHandler extends Handler {
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, page = 1) {
         const [ddocs, dpcount] = await paginate(
             discussion.getMulti(domainId),
@@ -99,7 +99,7 @@ class DiscussionMainHandler extends Handler {
 class DiscussionNodeHandler extends DiscussionHandler {
     @param('type', Types.String)
     @param('name', Types.String)
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, type: string, _name: string, page = 1) {
         let name: ObjectID | string | number;
         if (ObjectID.isValid(_name)) name = new ObjectID(_name);
@@ -177,7 +177,7 @@ class DiscussionCreateHandler extends DiscussionHandler {
 
 class DiscussionDetailHandler extends DiscussionHandler {
     @param('did', Types.ObjectID)
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, did: ObjectID, page = 1) {
         const dsdoc = this.user.hasPriv(PRIV.PRIV_USER_PROFILE)
             ? await discussion.getStatus(domainId, did, this.user._id)
diff --git a/packages/hydrooj/src/handler/domain.ts b/packages/hydrooj/src/handler/domain.ts
index 01ef32788..ba2d08fe4 100644
--- a/packages/hydrooj/src/handler/domain.ts
+++ b/packages/hydrooj/src/handler/domain.ts
@@ -1,4 +1,8 @@
-import { RoleAlreadyExistError, ValidationError } from '../error';
+import moment from 'moment-timezone';
+import {
+    RoleAlreadyExistError, ValidationError, DomainJoinForbiddenError,
+    DomainJoinAlreadyMemberError, InvalidJoinInvitationCodeError,
+} from '../error';
 import * as user from '../model/user';
 import * as domain from '../model/domain';
 import { DOMAIN_SETTINGS, DOMAIN_SETTINGS_BY_KEY } from '../model/setting';
@@ -10,7 +14,7 @@ import {
 } from '../service/server';
 
 class DomainRankHandler extends Handler {
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, page = 1) {
         const [dudocs, upcount, ucount] = await paginate(
             domain.getMultiInDomain(domainId).sort({ rp: -1 }),
@@ -184,6 +188,75 @@ class DomainRoleHandler extends ManageHandler {
     }
 }
 
+class DomainJoinApplicationsHandler extends ManageHandler {
+    async get() {
+        const r = await domain.getRoles(this.domain);
+        const roles = r.map((role) => role._id).sort();
+        const rolesWithText = roles.map((role) => [role, role]);
+        const joinSettings = domain.getJoinSettings(this.domain, roles);
+        const expirations = { ...domain.JOIN_EXPIRATION_RANGE };
+        if (!joinSettings) delete expirations[domain.JOIN_EXPIRATION_KEEP_CURRENT];
+        this.response.template = 'domain_join_applications.html';
+        this.response.body = { rolesWithText, joinSettings, expirations };
+    }
+
+    @param('method', Types.UnsignedInt)
+    @param('role', Types.String, true)
+    @param('expire', Types.UnsignedInt, true)
+    @param('invitationCode', Types.String, true)
+    async post(domainId: string, method: number, role: string, expire: number, invitationCode = '') {
+        const r = await domain.getRoles(this.domain);
+        const roles = r.map((rl) => rl._id);
+        const current = domain.getJoinSettings(this.domain, roles);
+        if (!domain.JOIN_METHOD_RANGE[method]) throw new ValidationError('method');
+        let joinSettings;
+        if (method === domain.JOIN_METHOD_NONE) joinSettings = null;
+        else {
+            if (!roles.includes(role)) throw new ValidationError('role');
+            if (!domain.JOIN_EXPIRATION_RANGE[expire]) throw new ValidationError('expire');
+            if (!current && expire === domain.JOIN_EXPIRATION_KEEP_CURRENT) throw new ValidationError('expire');
+            joinSettings = { method, role };
+            if (method === domain.JOIN_METHOD_CODE) joinSettings.code = invitationCode;
+            if (expire === domain.JOIN_EXPIRATION_KEEP_CURRENT) {
+                joinSettings.expire = current.expire;
+            } else if (expire === domain.JOIN_EXPIRATION_UNLIMITED) joinSettings.expire = null;
+            else joinSettings.expire = moment().add(expire, 'hours').toDate();
+        }
+        await domain.edit(this.domain._id, { join: joinSettings });
+        this.back();
+    }
+}
+
+class DomainJoinHandler extends Handler {
+    joinSettings: any;
+
+    async prepare() {
+        const r = await domain.getRoles(this.domain);
+        const roles = r.map((role) => role._id);
+        this.joinSettings = domain.getJoinSettings(this.domain, roles);
+        if (!this.joinSettings) throw new DomainJoinForbiddenError(this.domain._id);
+        if (this.user.role !== 'default') throw new DomainJoinAlreadyMemberError(this.domain._id, this.user._id);
+    }
+
+    // @base.require_priv(builtin.PRIV_USER_PROFILE)
+    @param('code', Types.String, true)
+    async get(domainId: string, code: string) {
+        this.response.template = 'domain_join.html';
+        this.response.body = { joinSettings: this.joinSettings, code };
+    }
+
+    @param('code', Types.String, true)
+    async post(domainId: string, code: string) {
+        if (this.joinSettings.method === domain.JOIN_METHOD_CODE) {
+            if (this.joinSettings.code !== code) {
+                throw new InvalidJoinInvitationCodeError(this.domain._id);
+            }
+        }
+        await domain.setUserRole(this.domain._id, this.user._id, this.joinSettings.role);
+        this.response.redirect = this.url('domain_main');
+    }
+}
+
 class DomainSearchHandler extends Handler {
     @param('q', Types.String)
     async get(domainId: string, q: string) {
@@ -202,6 +275,8 @@ export async function apply() {
     Route('domain_user', '/domain/user', DomainUserHandler);
     Route('domain_permission', '/domain/permission', DomainPermissionHandler);
     Route('domain_role', '/domain/role', DomainRoleHandler);
+    Route('domain_join_applications', '/domain/join_applications', DomainJoinApplicationsHandler);
+    Route('domain_join', '/domain/join', DomainJoinHandler, PRIV.PRIV_USER_PROFILE);
     Route('domain_search', '/domain/search', DomainSearchHandler, PRIV.PRIV_USER_PROFILE);
 }
 
diff --git a/packages/hydrooj/src/handler/homework.ts b/packages/hydrooj/src/handler/homework.ts
index 312ec032e..b02bab638 100644
--- a/packages/hydrooj/src/handler/homework.ts
+++ b/packages/hydrooj/src/handler/homework.ts
@@ -55,7 +55,7 @@ class HomeworkMainHandler extends HomeworkHandler {
 
 class HomeworkDetailHandler extends HomeworkHandler {
     @param('tid', Types.ObjectID)
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, tid: ObjectID, page = 1) {
         const tdoc = await contest.get(domainId, tid, document.TYPE_HOMEWORK);
         const [tsdoc, pdict] = await Promise.all([
diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index 0ae21d130..2e8feeb28 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -57,7 +57,7 @@ class ProblemHandler extends Handler {
 }
 
 class ProblemMainHandler extends ProblemHandler {
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     @param('q', Types.String, true)
     async get(domainId: string, page = 1, q = '') {
         this.response.template = 'problem_main.html';
@@ -103,7 +103,7 @@ class ProblemMainHandler extends ProblemHandler {
 }
 
 class ProblemCategoryHandler extends ProblemHandler {
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     @param('category', Types.String, null, parseCategory)
     async get(domainId: string, page = 1, category: string[]) {
         this.response.template = 'problem_main.html';
@@ -469,7 +469,7 @@ class ProblemDataDownloadHandler extends ProblemDetailHandler {
 }
 
 class ProblemSolutionHandler extends ProblemDetailHandler {
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, page = 1) {
         this.response.template = 'problem_solution.html';
         this.checkPerm(PERM.PERM_VIEW_PROBLEM_SOLUTION);
diff --git a/packages/hydrooj/src/handler/record.ts b/packages/hydrooj/src/handler/record.ts
index 1e91d65f1..57d6074c3 100644
--- a/packages/hydrooj/src/handler/record.ts
+++ b/packages/hydrooj/src/handler/record.ts
@@ -15,7 +15,7 @@ import { Rdoc } from '../interface';
 const RecordHandler = contest.ContestHandlerMixin(Handler);
 
 class RecordListHandler extends RecordHandler {
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     @param('pid', Types.String, true)
     @param('tid', Types.ObjectID, true)
     @param('uidOrName', Types.String, true)
diff --git a/packages/hydrooj/src/handler/training.ts b/packages/hydrooj/src/handler/training.ts
index f0426e1ba..1ddb8b2a5 100644
--- a/packages/hydrooj/src/handler/training.ts
+++ b/packages/hydrooj/src/handler/training.ts
@@ -54,7 +54,7 @@ async function _parseDagJson(domainId, dag) {
 }
 
 class TrainingMainHandler extends Handler {
-    @param('page', Types.UnsignedInt, true)
+    @param('page', Types.PositiveInt, true)
     async get(domainId: string, page = 1) {
         const [tdocs, tpcount] = await paginate(
             training.getMulti(domainId),
diff --git a/packages/hydrooj/src/loader.ts b/packages/hydrooj/src/loader.ts
index 24af4ad63..f6525a827 100644
--- a/packages/hydrooj/src/loader.ts
+++ b/packages/hydrooj/src/loader.ts
@@ -106,6 +106,13 @@ async function executeCommand(input: string) {
     }
 }
 
+async function reload(count = 1) {
+    console.log('Reloading');
+    await stopWorker();
+    console.log('Worker stopped');
+    await startWorker(count);
+}
+
 async function messageHandler(worker: cluster.Worker, msg: any) {
     if (!msg) msg = worker;
     if (msg.event) {
@@ -120,10 +127,7 @@ async function messageHandler(worker: cluster.Worker, msg: any) {
         } else if (msg.event === 'stat') {
             global.Hydro.stat.reqCount += msg.count;
         } else if (msg.event === 'restart') {
-            console.log('Restarting');
-            await stopWorker();
-            console.log('Worker stopped');
-            await startWorker(msg.count);
+            await reload(msg.count);
         } else if (msg.event === 'run') {
             await executeCommand(msg.command);
         }
diff --git a/packages/hydrooj/src/model/domain.ts b/packages/hydrooj/src/model/domain.ts
index 147d01e64..fca611319 100644
--- a/packages/hydrooj/src/model/domain.ts
+++ b/packages/hydrooj/src/model/domain.ts
@@ -1,11 +1,34 @@
 import { Dictionary } from 'lodash';
+import { Collection } from 'mongodb';
 import { BUILTIN_ROLES, PRIV } from './builtin';
 import { DomainDoc } from '../interface';
 import * as db from '../service/db';
 
-const coll = db.collection('domain');
+const coll: Collection<DomainDoc> = db.collection('domain');
 const collUser = db.collection('domain.user');
 
+export const JOIN_METHOD_NONE = 0;
+export const JOIN_METHOD_ALL = 1;
+export const JOIN_METHOD_CODE = 2;
+export const JOIN_METHOD_RANGE = {
+    [JOIN_METHOD_NONE]: 'No user is allowed to join this domain',
+    [JOIN_METHOD_ALL]: 'Any user is allowed to join this domain',
+    [JOIN_METHOD_CODE]: 'Any user is allowed to join this domain with an invitation code',
+};
+
+export const JOIN_EXPIRATION_KEEP_CURRENT = 0;
+export const JOIN_EXPIRATION_UNLIMITED = -1;
+
+export const JOIN_EXPIRATION_RANGE = {
+    [JOIN_EXPIRATION_KEEP_CURRENT]: 'Keep current expiration',
+    3: 'In 3 hours',
+    24: 'In 1 day',
+    [24 * 3]: 'In 3 days',
+    [24 * 7]: 'In 1 week',
+    [24 * 30]: 'In 1 month',
+    [JOIN_EXPIRATION_UNLIMITED]: 'Never expire',
+};
+
 export async function add(domainId: string, owner: number, name: string, bulletin: string) {
     const ddoc: DomainDoc = {
         _id: domainId,
@@ -32,9 +55,11 @@ export function edit(domainId: string, $set: any) {
     return coll.updateOne({ _id: domainId }, { $set });
 }
 
-export async function inc(domainId: string, field: string, n: number): Promise<number | null> {
+export async function inc(domainId: string, field: any, n: number): Promise<number | null> {
     const res = await coll.findOneAndUpdate(
         { _id: domainId },
+        // FIXME
+        // @ts-ignore
         { $inc: { [field]: n } },
         { returnOriginal: false },
     );
@@ -52,6 +77,8 @@ export function setUserRole(domainId: string, uid: number, role: string) {
     return collUser.updateOne({ uid, domainId }, { role }, { upsert: true });
 }
 
+export async function getRoles(domainId: string): Promise<any[]>
+export async function getRoles(domain: DomainDoc): Promise<any[]>
 export async function getRoles(arg: string | DomainDoc) {
     let ddoc: DomainDoc;
     if (typeof arg === 'string') ddoc = await get(arg);
@@ -144,6 +171,15 @@ export async function getDictUserByDomainId(uid: number) {
     return dudict;
 }
 
+export function getJoinSettings(ddoc: DomainDoc, roles: string[]) {
+    if (!ddoc.join) return null;
+    const joinSettings = ddoc.join;
+    if (joinSettings.method === JOIN_METHOD_NONE) return null;
+    if (!roles.includes(joinSettings.role)) return null;
+    if (joinSettings.expire && joinSettings.expire < new Date()) return null;
+    return joinSettings;
+}
+
 export async function getPrefixSearch(prefix: string, limit = 50) {
     const $regex = new RegExp(prefix, 'mi');
     const ddocs = await coll.find({
@@ -153,6 +189,14 @@ export async function getPrefixSearch(prefix: string, limit = 50) {
 }
 
 global.Hydro.model.domain = {
+    JOIN_METHOD_NONE,
+    JOIN_METHOD_ALL,
+    JOIN_METHOD_CODE,
+    JOIN_METHOD_RANGE,
+    JOIN_EXPIRATION_KEEP_CURRENT,
+    JOIN_EXPIRATION_UNLIMITED,
+    JOIN_EXPIRATION_RANGE,
+
     getRoles,
     add,
     inc,
@@ -170,5 +214,6 @@ global.Hydro.model.domain = {
     incUserInDomain,
     getMultiInDomain,
     getDictUserByDomainId,
+    getJoinSettings,
     getPrefixSearch,
 };
diff --git a/packages/hydrooj/src/service/server.ts b/packages/hydrooj/src/service/server.ts
index 1aaeeecd7..20c87e0fb 100644
--- a/packages/hydrooj/src/service/server.ts
+++ b/packages/hydrooj/src/service/server.ts
@@ -47,15 +47,15 @@ interface ParamOption {
 }
 
 // eslint-disable-next-line no-shadow
-export enum Types { String, Int, UnsignedInt, Float, ObjectID, Boolean, Date, Time }
+export enum Types { String, Int, UnsignedInt, PositiveInt, Float, ObjectID, Boolean, Date, Time }
 
 const Tools: Array<[Converter, Validator, boolean?]> = [
     [(v) => v.toString(), null],
     [(v) => parseInt(v, 10), (v) => isSafeInteger(parseInt(v, 10))],
+    [(v) => parseInt(v, 10), (v) => parseInt(v, 10) >= 0],
     [(v) => parseInt(v, 10), (v) => parseInt(v, 10) > 0],
     [(v) => parseFloat(v), (v) => {
         const t = parseFloat(v);
-        console.log(t);
         return t && !Number.isNaN(t) && Number.isFinite(t);
     }],
     [(v) => new ObjectID(v), ObjectID.isValid],
@@ -117,8 +117,7 @@ export function param(name: string, ...args: any): MethodDecorator {
             if (args[cursor] !== null) v.validate = args[cursor];
             isValidate = false;
         } else {
-            const I = args[cursor];
-            v.convert = I;
+            v.convert = args[cursor];
         }
         cursor++;
     }