What is the default algorithm?

Short answer

On HTTP and L7 TCP vServices, the default algorithm is Round Robin: requests are distributed to the servers in turn and equally, and the Weight values in the Backend Services are ignored. On the Network vService, the default is Round-Robin. If the LB Algorithm box in the Details section of the vService is not checked or is unchecked, this default is used.

How Does It Work?

• Round Robin: Each new request or connection goes to the next server in the list; when the end is reached, it returns to the beginning. All the servers receive the same share.
• Weight: Round Robin does not take Weight into account. If the capacities of the servers differ, Weighted Round Robin is selected; in this case, the Weight values are reflected in the shares.
• If the LB Algorithm box is unchecked: The algorithm returns to Round Robin (Round-Robin on Network), and the Persistence setting (L4 persistence on Network), if any, is also cleared.

Defaults by vService Type

vService type	Default algorithm	Does it use Weight
HTTP	Round Robin	No
L7 TCP	Round Robin	No
Network	Round-Robin	No

On the Network vService, when ANY - L3 is selected as the Protocol, the algorithm is automatically set to Round-Robin.

In TR7

• Panel: vService → Details → LB Algorithm; if the box is not checked, the vService runs with the default algorithm. When a vService with an algorithm other than the default or with a saved Persistence is opened, the box comes checked.
• WEB-CLI: If --algorithm is not given, the default is roundrobinNoWeight (Round Robin). The roundrobin value, on the other hand, is Weighted Round Robin (distribution algorithm).
• Monitoring: The Load Balancer Management screen of the vService shows with which algorithm the traffic is distributed.

Common Misconceptions

• "I entered Weight, so the default algorithm applies it." The default Round Robin ignores Weight; Weighted Round Robin must be selected.
• "roundrobin in WEB-CLI is the default algorithm." roundrobin is Weighted Round Robin; the default is roundrobinNoWeight.
• "The default algorithm keeps the user on the same server." Round Robin does not provide persistence; for that, Persistence or a self-persistent algorithm is required.

How it is done in the documentation

• HTTP (L7) vService · LB Algorithm
• Network vService · LB Algorithm
• WEB-CLI · lb service · The Distribution Algorithm

Related questions

• What is the difference between Round Robin and Weighted Round Robin?
• Which load balancing algorithms are supported?
• Why is traffic not distributed evenly across the servers?