Load balancers

Each new request goes to the next server in turn. Fair when servers and requests are alike.

Round robin where bigger servers get more turns, in proportion to a weight you set.

Each request goes to the server with the fewest requests in progress. Copes with requests of very different lengths.

Least connections, adjusted for how much each server can handle at once.

Prefers the server that has been answering fastest, together with how much it has in progress.

Hashes the client's IP address to pick a server, so the same client keeps reaching the same server.

Picks a server at random. Even on average, with no shared state between balancers.

Picks two servers at random and sends the request to the less busy one. Close to least connections, far cheaper.

Servers report their own load, such as CPU and memory, and work goes to whichever has the most room.