diff --git a/app/server.ts b/app/server.ts
index c5262e3..1eaf5c3 100644
--- a/app/server.ts
+++ b/app/server.ts
@@ -4,11 +4,11 @@ import next from "next";
 import { Server } from "socket.io";
 import type { SocketServer } from "@/types";
 import { Field } from "@/utils/game";
+import * as redis from "@/utils/redis";
 
 const dev = process.env.NODE_ENV !== "production";
 const hostname = "localhost";
 const port = 3000;
-const sessions = new Map<string, "alive" | "dead">();
 
 async function main() {
   const app = next({ dev, hostname, port });
@@ -24,8 +24,8 @@ async function main() {
 
   io.use(async (socket, next) => {
     const { sessionId } = socket.handshake.auth;
-    const sessionState = sessions.get(sessionId);
-    if (sessions.get(sessionId) === "dead") {
+    const sessionState = await redis.getSession(sessionId);
+    if (sessionState === "dead") {
       return next(new Error("dead"));
     }
     socket.data.sessionId = sessionState
@@ -34,8 +34,8 @@ async function main() {
     next();
   });
 
-  io.on("connection", (socket) => {
-    sessions.set(socket.data.sessionId, "alive");
+  io.on("connection", async (socket) => {
+    await redis.startSession(socket.data.sessionId);
     socket.emit("sessionAlive", socket.data.sessionId);
 
     clientsCount++;
@@ -45,7 +45,7 @@ async function main() {
 
     socket.on("expose", async (index) => {
       if (field.exposeCell(index) === "dead") {
-        sessions.set(socket.data.sessionId, "dead");
+        await redis.killSession(socket.data.sessionId);
         socket.emit("sessionDead");
       } else {
         field = await field.handleComplete();
diff --git a/app/utils/redis.ts b/app/utils/redis.ts
index f2550ef..710d143 100644
--- a/app/utils/redis.ts
+++ b/app/utils/redis.ts
@@ -1,24 +1,40 @@
 import { Redis } from "ioredis";
 import _ from "lodash";
 
-const key = "field:data";
+const fieldKey = "field:data";
+const sessionKey = "user:sessions";
 
-function getClient() {
-  return new Redis(process.env["REDIS_URL"]!, { family: 6 });
-}
+const redis = new Redis(process.env["REDIS_URL"]!, { family: 6 });
 
 export async function decodeData() {
-  const redis = getClient();
-  const value = await redis.get(key);
+  const value = await redis.get(fieldKey);
   if (typeof value !== "string" || !value) {
-    throw new Error(`unexpected data on key: ${key}`);
+    throw new Error(`unexpected data on key: ${fieldKey}`);
   }
   return Array.from(value, (char) => char.charCodeAt(0));
 }
 
 export async function encodeData(value: number[]) {
-  const redis = getClient();
   const binaryString = Buffer.from(value).toString("binary");
-  await redis.set(key, binaryString);
+  await redis.set(fieldKey, binaryString);
   return value;
 }
+
+export async function getSession(sessionId: string) {
+  const value = await redis.hget(sessionKey, sessionId);
+  return value === "alive" || value === "dead" ? value : null;
+}
+
+export async function startSession(sessionId: string) {
+  return redis.hset(sessionKey, sessionId, "alive");
+}
+
+export async function killSession(sessionId: string) {
+  return redis.hset(sessionKey, sessionId, "dead");
+}
+
+export async function reviveSessions() {
+  const sessions = await redis.hkeys(sessionKey);
+  const args = sessions.flatMap((sessionId) => [sessionId, "alive"]);
+  redis.hset(sessionKey, ...args);
+}