57 lines
1.6 KiB
Lua
57 lines
1.6 KiB
Lua
-- An affinity mode which makes sure connections are rebalanced when a deployment is scaled.
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-- The advantage of this mode is that the load on the pods will be redistributed.
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-- The drawback of this mode is that, when scaling up a deployment, roughly (n-c)/n users
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-- will lose their session, where c is the current number of pods and n is the new number of
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-- pods.
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--
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local balancer_sticky = require("balancer.sticky")
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local math = require("math")
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local resty_chash = require("resty.chash")
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local util = require("util")
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local _M = balancer_sticky:new()
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-- Consider the situation of N upstreams one of which is failing.
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-- Then the probability to obtain failing upstream after M iterations would be close to (1/N)**M.
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-- For the worst case (2 upstreams; 20 iterations) it would be ~10**(-6)
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-- which is much better then ~10**(-3) for 10 iterations.
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local MAX_UPSTREAM_CHECKS_COUNT = 20
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function _M.new(self, backend)
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local nodes = util.get_nodes(backend.endpoints)
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local o = {
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name = "sticky_balanced",
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instance = resty_chash:new(nodes)
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}
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setmetatable(o, self)
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self.__index = self
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balancer_sticky.sync(o, backend)
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return o
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end
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function _M.get_routing_key(self)
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return self:get_cookie(), nil
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end
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function _M.set_routing_key(self, key)
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self:set_cookie(key)
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end
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function _M.pick_new_upstream(self, failed_upstreams)
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for i = 1, MAX_UPSTREAM_CHECKS_COUNT do
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local key = string.format("%s.%s.%s", ngx.now() + i, ngx.worker.pid(), math.random(999999))
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local new_upstream = self.instance:find(key)
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if not failed_upstreams[new_upstream] then
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return new_upstream, key
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end
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end
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return nil, nil
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end
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return _M
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