我正在将RabbitMQ的Bunny gem与Rails集成,我是否应该在Rails以应用程序启动启动的初始化程序中启动Bunny线程,或者在单独的rake任务中执行它,以便我可以在单独的进程中启动它?
我认为如果我只生成消息,那么我需要在Rails初始化程序中执行它,以便它可以在应用程序中使用,但如果我正在消耗我应该在单独的rake任务中执行,这是正确的吗?
答案 0 :(得分:5)
你是对的:你不应该从Rails应用程序本身消费。 Rails应用程序应该是一个生产者,在这种情况下,初始化程序是启动Bunny实例的正确位置。
我基本上在我的Rails应用程序中有这个代码,它将消息发布到RabbitMQ:
# config/initializers/bunny.rb
MESSAGING_SERVICE = MessagingService.new(ENV.fetch("AMQP_URL"))
MESSAGING_SERVICE.start
# app/controllers/application_controller.rb
class ApplicationController
def messaging_service
MESSAGING_SERVICE
end
end
# app/controllers/uploads_controller.rb
class UploadsController < ApplicationController
def create
# save the model
messaging_service.publish_resize_image_request(model.id)
redirect_to uploads_path
end
end
# lib/messaging_service.rb
class MessagingService
def initialize(amqp_url)
@bunny = Bunny.new(amqp_url)
@bunny.start
at_exit { @bunny.stop }
end
attr_reader :bunny
def publish_resize_image_request(image_id)
resize_image_exchange.publish(image_id.to_s)
end
def resize_image_exchange
@resize_image_exchange ||=
channel.exchange("resize-image", passive: true)
end
def channel
@channel ||= bunny.channel
end
end
对于消费消息,我更喜欢在没有涉及Rake的情况下启动可执行文件。 Rake将分叉一个新进程,它将占用更多内存。
# bin/image-resizer-worker
require "bunny"
bunny = Bunny.new(ENV.fetch("AMQP_URL"))
bunny.start
at_exit { bunny.stop }
channel = bunny.channel
# Tell RabbitMQ to send this worker at most 2 messages at a time
# Else, RabbitMQ will send us as many messages as we can absorb,
# which would be 100% of the queue. If we have multiple worker
# instances, we want to load-balance between each of them.
channel.prefetch(2)
exchange = channel.exchange("resize-image", type: :direct, durable: true)
queue = channel.queue("resize-image", durable: true)
queue.bind(exchange)
queue.subscribe(manual_ack: true, block: true) do |delivery_info, properties, payload|
begin
upload = Upload.find(Integer(payload))
# somehow, resize the image and/or post-process the image
# Tell RabbitMQ we processed the message, in order to not see it again
channel.acknowledge(delivery_info.delivery_tag, false)
rescue ActiveRecord::RecordNotFound => _
STDERR.puts "Model does not exist: #{payload.inspect}"
# If the model is not in the database, we don't want to see this message again
channel.acknowledge(delivery_info.delivery_tag, false)
rescue Errno:ENOSPC => e
STDERR.puts "Ran out of disk space resizing #{payload.inspect}"
# Do NOT ack the message, in order to see it again at a later date
# This worker, or another one on another host, may have free space to
# process the image.
rescue RuntimeError => e
STDERR.puts "Failed to resize #{payload}: #{e.class} - #{e.message}"
# The fallback should probably be to ack the message.
channel.acknowledge(delivery_info.delivery_tag, false)
end
end
尽管如此,你可能会更好地使用预先构建的宝石并使用Rails&#39;抽象,ActiveJob。