8ee4f308a4
Introduces a new db key "<service>-previous" to track which instance was last selected for a particular service. This allows for filtering the list of available instances to exclude the instance that was last picked, to ensure a (slightly) more even distribution of traffic. There's still the possiblity of the following scenario, however: :service instances > 2 /:service request #1 -> instance #1 /:service request #2 -> instance #2 /:service request #3 -> instance #1 /:service request #4 -> instance #2 where there are many ignored instances for a particular service. One possible solution would be to implement the "<service>-previous" value to be a list, rather than a single value, and push to that list until only one element is left in the original "instance" array after filtering, and then delete the "<service>-previous" key.
89 lines
2.3 KiB
Elixir
89 lines
2.3 KiB
Elixir
defmodule Instances do
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@fallback_suffix Application.fetch_env!(:farside, :fallback_suffix)
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@update_file Application.fetch_env!(:farside, :update_file)
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@services_json Application.fetch_env!(:farside, :services_json)
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@service_prefix Application.fetch_env!(:farside, :service_prefix)
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def init() do
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File.rename(@update_file, "#{@update_file}-prev")
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update
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end
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def request(url) do
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cond do
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System.get_env("FARSIDE_TEST") ->
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:good
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true ->
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case HTTPoison.get(url) do
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{:ok, %HTTPoison.Response{status_code: 200}} ->
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# TODO: Add validation of results, not just status code
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:good
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_ ->
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:bad
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end
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end
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end
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def update do
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{:ok, file} = File.read(@services_json)
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{:ok, json} = Poison.decode(file, as: [%Service{}])
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# Loop through all instances and check each for availability
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for service <- json do
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IO.puts "======== " <> service.type
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result = Enum.filter(service.instances, fn(instance_url) ->
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IO.puts " " <> instance_url
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request(instance_url <> service.test_url) == :good
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end)
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add_to_redis(service, result)
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log_results(service.type, result)
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end
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end
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def add_to_redis(service, instances) do
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# Remove previous list of instances
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Redix.command(:redix, [
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"DEL",
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"#{@service_prefix}#{service.type}"
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])
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# Update with new list of available instances
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Redix.command(:redix, [
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"LPUSH",
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"#{@service_prefix}#{service.type}"
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] ++ instances)
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# Set fallback to one of the available instances,
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# or the default instance if all are "down"
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if Enum.count(instances) > 0 do
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Redix.command(:redix, [
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"SET",
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"#{service.type}#{@fallback_suffix}",
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Enum.random(instances)
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])
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else
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Redix.command(:redix, [
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"SET",
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"#{service.type}#{@fallback_suffix}",
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service.fallback
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])
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end
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end
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def log_results(service_name, results) do
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{:ok, file} = File.open(@update_file, [:append, {:delayed_write, 100, 20}])
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IO.write(file, "#{service_name}: #{inspect(results)}\n")
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File.close(file)
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end
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end
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Instances.init()
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# Add UTC time of last update
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Redix.command(:redix, [
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"SET",
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"last_updated",
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Calendar.strftime(DateTime.utc_now(), "%c")
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])
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