57 lines
2 KiB
Ruby
57 lines
2 KiB
Ruby
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# frozen_string_literal: true
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module Gitlab
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module Database
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module LoadBalancing
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class ServiceDiscovery
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class Sampler
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def initialize(max_replica_pools:, seed: Random.new_seed)
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# seed must be set once and consistent
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# for every invocation of #sample on
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# the same instance of Sampler
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@seed = seed
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@max_replica_pools = max_replica_pools
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end
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def sample(addresses)
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return addresses if @max_replica_pools.nil? || addresses.count <= @max_replica_pools
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::Gitlab::Database::LoadBalancing::Logger.info(
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event: :host_list_limit_exceeded,
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message: "Host list length exceeds max_replica_pools so random hosts will be chosen.",
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max_replica_pools: @max_replica_pools,
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total_host_list_length: addresses.count,
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randomization_seed: @seed
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)
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# First sort them in case the ordering from DNS server changes
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# then randomly order all addresses using consistent seed so
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# this process always gives the same set for this instance of
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# Sampler
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addresses = addresses.sort
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addresses = addresses.shuffle(random: Random.new(@seed))
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# Group by hostname so that we can sample evenly across hosts
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addresses_by_host = addresses.group_by(&:hostname)
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selected_addresses = []
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while selected_addresses.count < @max_replica_pools
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# Loop over all hostnames grabbing one address at a time to
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# evenly distribute across all hostnames
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addresses_by_host.each do |host, addresses|
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next if addresses.empty?
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selected_addresses << addresses.pop
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break unless selected_addresses.count < @max_replica_pools
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end
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end
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selected_addresses
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end
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end
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end
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end
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end
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end
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