Azure Cache for Redis Integration¶

This recipe shows how to integrate Azure Cache for Redis with a Node.js Express application for session storage and data caching.

Overview¶

Redis is an in-memory data store frequently used as a cache or session provider. On Azure App Service, a shared session state (via Redis) is required if you are using multiple instances (scale-out) or need persistent sessions during redeployments.

Architecture¶

flowchart TD
    Client[Client] --> App[App Service]
    App --> Redis[Azure Cache for Redis]
    App -.-> MI[Managed Identity]
    MI -.-> Entra[Microsoft Entra ID]

How to read this diagram: Solid arrows show runtime data flow. Dashed arrows show identity and authentication.

Prerequisites¶

Azure Cache for Redis instance
Azure App Service with Node.js
Access key or connection string for the Redis instance

Implementation¶

1. Install Dependencies¶

npm install ioredis express-session connect-redis

2. Basic Redis Setup¶

const Redis = require('ioredis');

// Connect using REDIS_CONNECTION_STRING from App Service configuration
const redisClient = new Redis(process.env.REDIS_CONNECTION_STRING, {
  tls: {
    // Azure Cache for Redis uses valid TLS certificates;
    // the default (rejectUnauthorized: true) is correct and secure.
  },
  // Ensure the connection is kept alive
  keepAlive: 1000,
  retryStrategy: (times) => Math.min(times * 50, 2000)
});

redisClient.on('error', (err) => console.error('Redis Client Error', err));

module.exports = redisClient;

3. Session Storage with express-session¶

const express = require('express');
const session = require('express-session');
const RedisStore = require('connect-redis').default;
const redisClient = require('./redis-client');

const app = express();

app.use(session({
  store: new RedisStore({ client: redisClient }),
  secret: process.env.SESSION_SECRET || 'keyboard cat',
  resave: false,
  saveUninitialized: false,
  cookie: {
    secure: true, // Recommended for App Service (HTTPS by default)
    httpOnly: true,
    maxAge: 86400000 // 1 day
  }
}));

4. Caching Patterns¶

async function getCachedData(key, fetchFn) {
  const cachedValue = await redisClient.get(key);
  if (cachedValue) {
    return JSON.parse(cachedValue);
  }

  const freshData = await fetchFn();
  await redisClient.set(key, JSON.stringify(freshData), 'EX', 3600); // 1-hour expiration
  return freshData;
}

Verification¶

Test the integration by logging session data or reading/writing to Redis:

# Set environment variables
az webapp config appsettings set --name $APP_NAME --resource-group $RG --settings REDIS_CONNECTION_STRING="rediss://:<key>@<host>:6380" SESSION_SECRET="super-secret" --output json

Troubleshooting¶

Connection Refused (6380): Ensure you are using rediss:// (with an extra 's') to specify SSL/TLS connection.
Session Loss: If your app scales to multiple instances, ensure all instances point to the same Redis instance for session state.
Performance: Monitor Redis metrics in the Azure Portal. High latency might indicate a need for a larger Redis SKU or colocating your Redis and App Service in the same region.

Advanced Topics¶

Coming Soon

Run It in the Portal¶

Portal view: Identity blade (optional Microsoft Entra authentication path)¶

The Identity blade visible here is relevant only if you switch this recipe from the default REDIS_CONNECTION_STRING key-based flow to a Microsoft Entra-authenticated Redis connection. In the visible pre-enable state, System assigned is selected and Status is still Off; turning it On is the Portal step that creates the app identity before any Redis-side Entra mapping can be granted. For the recipe's default flow, keep using the REDIS_CONNECTION_STRING app setting with the ioredis new Redis(process.env.REDIS_CONNECTION_STRING, {...}) configuration shown above.