Stateful vs Stateless Load Balancing on VPS: How to Choose and Implement

[johny899]

Have you ever tried to balance traffic across a VPS and thought to yourself, this is crazy? I have been there too. I recall looking at logs and errors and saying, "What could even be going on?" This was about the time I started understanding the difference between stateful load balancing and stateless load balancing, and suddenly it all made sense.

So What's the Difference between Stateful and Stateless Load Balancing??​

Let's make this fun!

Stateful load balancing is like being a shop owner who recognizes you are there and gives you the same thing each time. Stateless load balancing is like going to a different shop each time you go, and any worker can serve you.

Both techniques work great (respectively, of course)!

Stateful Load Balancing​

Stateful load balancing will take a user to the same backend server for each request.

I use stealthy load balancing when my app will not work if a user switches servers. Some apps just will not work with switching servers.

Advantages

• The same user will always hit the same server.
• Fantastic for apps with log-in or carts.
• Stability and smoothness for the user experience.

Drawbacks

• Scaling is hard because traffic isn't evenly load-balanced.
• One server can become overloaded while the others remain free.

I’ve seen one VPS overloaded with work that forced the other two to idle. Not fun.

Stateless Load Balancing (Fast and Easy)​

Stateless Load Balancing does not remember anything. A request just hits an available server.

Feels excellent when you want fast connections and simple traffic distribution.

Advantages

• Traffic is evenly distributed.
• Scaling is very easy.
• Simple configuration.

Reasons Why It Can Be An Issue

• Sessions will be lost if your app relies on the user to log in.
• You will need to store the sessions elsewhere such as Redis or a database.

I cannot tell you how many applications I have forgotten to set up storage for sessions and, on the login page, it kept kicking people out!

This One is Simple - How I Choose Between the Two​

Take a look at my simple rules:

When to Pick Stateful

• Your application has login sessions
• You are storing data in memory on the servers
• You want consistent behavior

When to Pick Stateless

• You want speed
• You want easier scaling
• You are using either Redis, Memcached, or a database to store sessions

Look! Not too difficult!

Thanks for Making it Till the End​

Stateful and stateless load balancing both will work great in a VPS environment. You simply have to pick the right one for your application. If your application requires memory and sessions - pick stateful. If you are looking for speed and the less memory for scaling - pick stateless.