What is the difference between Round Robin and Weighted Round Robin?

Short answer

Both distribute requests to the servers in turn; the difference is in Weight. Round Robin ignores the Weight values in the Backend Services and gives each server an equal share. Weighted Round Robin gives each server a share in proportion to its Weight: of two servers with Weights of 3 and 1, the first receives 3 out of every 4 requests. If the Weights are equal or not entered at all (default value 1), the two produce the same distribution.

Comparison

	Round Robin	Weighted Round Robin
Distribution	In turn, equal	In turn, in proportion to Weight
Weight field	Ignored	Applied (1–256; default 1)
Suitable situation	The servers have the same capacity	The capacities of the servers differ
Is it the default	Yes	No
WEB-CLI value	roundrobinNoWeight	roundrobin
Network vService equivalent	Round-Robin (rr)	Weighted Round-Robin (wrr)

How Does It Work?

• Round Robin: For servers A, B, C, the order is A → B → C → A…
• Weighted Round Robin: The share of each server = Weight ÷ total Weight. For A=2, B=1, 2 out of every 3 requests go to A and 1 to B.
• Neither algorithm looks at the current load or the number of open connections of the servers. If the connection durations differ greatly, Least Connection gives a more balanced result.

In TR7

• The algorithm is selected in the vService → Details → LB Algorithm box.
• Weight is entered in the Details section of the Backend Service form; in a Backend Group, it is entered separately for each server row (Backend Groups · Weight).
• On the Live Stats screen, the Weight of each Backend Service appears with the W= suffix at the end of the name cell (Live Stats · Backend Services).
• On the Network vService, Weight is applied only in Weighted Round-Robin also while Protocol ANY - L3 is selected or Port Range is on.

Common Misconceptions

• "If I enter Weight with Round Robin, the distribution changes." It does not change; Weight is applied only in algorithms that use Weight (e.g. Weighted Round Robin).
• "roundrobin in WEB-CLI is the version without Weight." roundrobin is Weighted Round Robin; the version without Weight is roundrobinNoWeight.
• "Weighted Round Robin adjusts the load according to the current state of the servers." The Weights are fixed; the current load is not looked at.
• "A server is taken out of service by entering Weight 0." Weight is at least 1; to take a server out of traffic, Maintenance Mode is used (Maintenance Mode does not apply to a Network vService; the Backend Service is removed from the vService's Backend Services list).

How it is done in the documentation

• HTTP (L7) vService · Algorithms
• Backend Services · Weight
• Network vService · Algorithms

Related questions

• How do I distribute load proportionally across servers with different capacities?
• What is Weight, and how should it be set?
• What is the default algorithm?