overview-8-how-expiring-keys-work.md

Let's delve deeper into how expiring keys work with real-world examples. Consider a common use case: a web application that uses Redis to manage user sessions.

Scenario: User Sessions

1. User Login:

   • When a user logs into a web application, a unique session ID is generated for that user.
   • The session ID is associated with the user's information, such as user ID, username, and access permissions.

   const sessionId = generateUniqueSessionId();
   const userId = 123;
   const sessionData = { username: 'john_doe', isAdmin: false };
   
   // Set the session key with an expiration time (e.g., 30 minutes)
   client.set(`session:${sessionId}`, JSON.stringify(sessionData), 'EX', 1800);

2. Checking User Authentication:

   • Throughout the user's interaction with the web application, the session ID is used to identify the user.
   • The web application checks the user's authentication by retrieving the session data from Redis.

   const sessionId = userProvidedSessionId;
   
   // Check if the session key exists and retrieve the session data
   client.get(`session:${sessionId}`, (err, sessionData) => {
     if (err) {
       console.error(err);
       // Handle error
     } else if (sessionData) {
       const userData = JSON.parse(sessionData);
       // User is authenticated, proceed with the request
     } else {
       // Session key does not exist or has expired
       // Redirect to login page or prompt for reauthentication
     }
   });

3. Expiration:

   • The session key in Redis is set to expire after a certain time (e.g., 30 minutes).
   • If the user remains active, each interaction with the web application resets the expiration time for the session key.

   const sessionId = userProvidedSessionId;
   
   // Extend the expiration time of the session key (e.g., 30 minutes)
   client.expire(`session:${sessionId}`, 1800);

4. Automatic Cleanup:

   • If the user logs out or if the session remains inactive for the specified time, the session key automatically expires and is removed from Redis.

Summary:

• The web application uses Redis keys to store session information, associating a unique session ID with user data.
• The expiration time for the session key ensures that inactive sessions are automatically cleaned up, preventing the Redis database from storing unnecessary data.
• The expiration time also adds a layer of security by limiting the validity period of a session, reducing the risk of unauthorized access if a session ID is compromised.

This is just one example of how expiring keys in Redis can be applied in a real-world scenario. The principle remains similar across various use cases where temporary data needs to be managed efficiently.