Round robin load balancing #96
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| @@ -79,9 +80,13 @@ public BackendHealthCheckOptions(bool enabled, TimeSpan interval, TimeSpan timeo | |||
| public BackendLoadBalancingOptions(LoadBalancingMode mode) | |||
| { | |||
| Mode = mode; | |||
| // Increment returns the new value and we want the first return value to be 0. | |||
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I'd make the first value random - that way all requests don't all start out hitting the same server.
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? Every request increments the counter for an even distribution. It shouldn't matter where it starts, I only wanted 0 because it conceptually meets expectations (start the the top of the list and cycle through all entries).
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In a distributed deployment of YARP, all YARP instances would start out choosing the same target server if initial choice is const. There is some merit to making it random, but i reckon the benefit is minimal to negligible. In a practical deployment, it is unlikely that many instances of YARP would be (re-)started at precisely the same time, and even if they were, there is a lot of entropy that would help minimize hotspots to some extent. Further, anyone doing round-robin probably doesn't care about hotspots anyway.
| @@ -41,7 +41,8 @@ public Task Invoke(HttpContext context) | |||
| var endpoints = endpointsFeature?.Endpoints | |||
| ?? throw new InvalidOperationException("The AvailableBackendEndpoints collection was not set."); | |||
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| var loadBalancingOptions = backend.Config.Value?.LoadBalancingOptions ?? default; | |||
| var loadBalancingOptions = backend.Config.Value?.LoadBalancingOptions | |||
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Why is this being read per request?
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Because it can be configured per route/backend, and can be changed if they are reloaded.
#72 While we debated more complex backend data storage mechanisms, I wanted to try something simple first. Built in algorithms can avail themselves of built in structures so I added the round robin state tracker to the existing BackendLoadBalancingOptions structure.