server: add upstream connection rebalancing #221
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Adds support for rebalancing upstream connections across the cluster. Every second each node calculates it's connection "balance", which is the ratio of the number of connections the node has locally to the cluster average. If a node finds it's balance exceeds the configured threshold, it will shed connections. Since the Piko cluster is typically hosted behind a load balancer, when connections are shed, clients will automatically reconnect to random node in the cluster, so eventually the nodes connections will be balanced. This does mean rebalancing isn't perfect, as an upstream may be disconnected and reconnect to the node that's already shedding connections, but it's the best we can do. It will cause minor disruption while upstreams reconnect, though the alternative is to overload Piko nodes with no way to rebalance load. By default rebalancing is disabled. Fixes #176.
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Adds support for rebalancing upstream connections across the cluster.
Every second each node calculates it's connection "balance", which is the ratio of the number of connections the node has locally to the cluster average. If a node finds it's balance exceeds the configured threshold, it will shed connections.
Since the Piko cluster is typically hosted behind a load balancer, when connections are shed, clients will automatically reconnect to random node in the cluster, so eventually the nodes connections will be balanced.
This does mean rebalancing isn't perfect, as an upstream may be disconnected and reconnect to the node that's already shedding connections, but it's the best we can do. It will cause minor disruption while upstreams reconnect, though the alternative is to overload Piko nodes with no way to rebalance load.
By default rebalancing is disabled.
Fixes #176.