How to deal with an external service failure in Open-Uri?

Question

In my Rails application, I am trying to extract several exchange rates from an external service and store them in the cache:

require 'open-uri'

module ExchangeRate

  def self.all
    Rails.cache.fetch("exchange_rates", :expires_in => 24.hours) { load_all }
  end

  private

    def self.load_all
      hashes = {}
      CURRENCIES.each do |currency|
        begin
          hash = JSON.parse(open(URI("http://api.fixer.io/latest?base=#{currency}")).read) #what if not available?
          hashes[currency] = hash["rates"]
        rescue Timeout::Error
          puts "Timeout"
        rescue OpenURI::Error => e
          puts e.message
        end
      end
      hashes
    end

end

This works great in development, but the production environment bothers me. How can I prevent caching of all this if the external service is unavailable? How can I guarantee that it ExchangeRate.allalways contains data, even if it is old and cannot be updated due to an external service failure?

I tried to add basic error handling, but I'm afraid this is not enough.

Answer 1

, , 24 , , - , load_all.

:

• , ExchangeRate.all ( nil, ):

  module ExchangeRate
    def self.all
      rates = Rails.cache.fetch("exchange_rates")
      UpdateCurrenciesJob.perform_later if rates.nil?
      rates
    end
  end
  

• ActiveJob, :

  class UpdateCurrenciesJob < ApplicationJob
    queue_as :default
  
    def perform(*_args)
      hashes = {}
      CURRENCIES.each do |currency|
        begin
          hash = JSON.parse(open(URI("http://api.fixer.io/latest?base=#{currency}")).read) # what if not available?
          hashes[currency] = hash['rates'].merge('updated_at' => Time.current)
        rescue Timeout::Error
          puts 'Timeout'
        rescue OpenURI::Error => e
          puts e.message
        end
  
        if hashes[currency].blank? || hashes[currency]['updated_at'] < Time.current - 24.hours
          # send a mail saying "this currency hasn't been updated"
        end
      end
  
      Rails.cache.write('exchange_rates', hashes)
    end
  end
  

• (4, 8, 12, 24). , , , , .