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Once a list of available URLs has been determined for a particular service, the list is written as "service -> [list of instances]" to a local redis connection. These can then be used in the greater routing logic to pick a random instance from the list, or use a fallback instance if none are determined to be available.
71 lines
1.5 KiB
Elixir
71 lines
1.5 KiB
Elixir
defmodule Service do
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defstruct [
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type: nil,
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test_url: nil,
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fallback: nil,
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instances: []
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]
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end
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defmodule Instances do
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def request(url) do
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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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def update(filename) do
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{:ok, conn} = Redix.start_link(
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"redis://localhost:6379",
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name: :redix
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)
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{:ok, file} = File.read(filename)
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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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result = Enum.filter(service.instances, fn(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(conn, service, result)
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end
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end
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def add_to_redis(conn, service, instances) do
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# Remove previous list of instances
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Redix.command(conn, [
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"DEL",
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service.type
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])
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# Update with new list of available instances
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Redix.command(conn, [
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"LPUSH",
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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(conn, [
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"SET",
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service.type <> "-fallback",
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Enum.random(instances)
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])
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else
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Redix.command(conn, [
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"SET",
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service.type <> "-fallback",
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service.fallback
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])
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end
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end
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end
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Instances.update("services.json")
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