Middleware

Sidekiq has a similar notion of middleware to Rack: these are small bits of code that can implement functionality. Sidekiq breaks middleware into client-side and server-side.

Client middleware runs before the pushing of the job to Redis and allows you to modify/stop the job before it gets pushed.
Server middleware runs 'around' job processing.

If you call perform_inline both client and server middleware will run.

Custom middleware

Sidekiq 5+ ships with no middleware out of the box. Various gems and services will install middleware to track jobs or provide additional features. You may also add your own (note that as of Sidekiq 7, you must include Sidekiq::ClientMiddleware or Sidekiq::ServerMiddleware in your client or server middleware, respectively)

Client middleware

You can use client middleware to add job metadata to the job before pushing it to Redis. The same job data will be available to the server middleware before the job is executed, if you need to set up some global state, e.g. current locale, current tenant in a multi-tenant app, etc.

Client middleware may receive the class argument as a Class object or a String containing the name of the class.

Not calling yield or returning anything other than job will result in no further middleware being called and the job will not be pushed to the queue. (Note that yield will return an equivalent value to job)

module MyMiddleware
  module Client
    class CustomerJobAttribute
      include Sidekiq::ClientMiddleware

      # @param [String, Class] job_class_or_string the class or string representation
      #    of the class of the job being queued
      # @param [Hash] job the full job payload
      #   * @see https://github.com/sidekiq/sidekiq/wiki/Job-Format
      # @param [String] queue the name of the queue the job was pulled from
      # @param [ConnectionPool] redis_pool the redis pool
      # @return [Hash, FalseClass, nil] if false or nil is returned,
      #   the job is not to be enqueued into redis, otherwise the block's
      #   return value is returned
      # @yield the next middleware in the chain or the enqueuing of the job
      def call(job_class_or_string, job, queue, redis_pool)
        # return false/nil to stop the job from going to redis
        return false if queue != 'default'
        job['customer'] = Customer.current_id
        yield
      end
    end
  end
end

Server middleware

You can use server middleware to do something around the execution of any job. The example below logs any exception from any job.

Not calling yield will result in no further middleware being called and the job's perform method will not be called.

class MyMiddleware::Server::ErrorLogger
  include Sidekiq::ServerMiddleware

  # @param [Object] job_instance the instance of the job that was queued
  # @param [Hash] job_payload the full job payload
  #   * @see https://github.com/sidekiq/sidekiq/wiki/Job-Format
  # @param [String] queue the name of the queue the job was pulled from
  # @yield the next middleware in the chain or worker `perform` method
  # @return [Void]
  def call(job_instance, job_payload, queue)
    begin
      yield
    rescue => ex
      puts ex.message
    end
  end
end

You may also pass options to the Middleware initializer when you register the middleware:

class MyMiddleware::Server::ErrorLogger
  def initialize(options=nil)
    # options == { :foo => 1, :bar => 2 }
  end
  def call(worker, job, queue)
    begin
      yield
    rescue => ex
      puts ex.message
    end
  end
end

Registering Middleware

Register your middleware as part of the chain:

Sidekiq.configure_client do |config|
  config.client_middleware do |chain|
    chain.add MyMiddleware::Client::CustomerJobAttribute
  end
end

Sidekiq.configure_server do |config|
  config.server_middleware do |chain|
    chain.add MyMiddleware::Server::ErrorLogger, :foo => 1, :bar => 2
  end
end

I'd suggest putting this code in config/initializers/sidekiq.rb in your Rails app.

Client middleware registered in both places

The jobs running in the Sidekiq server can themselves push new jobs to Sidekiq, thus acting as clients. You must configure your client middleware within the configure_server block also in that case:

Sidekiq.configure_client do |config|
  config.client_middleware do |chain|
    chain.add MyMiddleware::Client::CustomerJobAttribute
  end
end

Sidekiq.configure_server do |config|
  config.client_middleware do |chain|
    chain.add MyMiddleware::Client::CustomerJobAttribute
  end
  config.server_middleware do |chain|
    chain.add MyMiddleware::Server::ErrorLogger, :foo => 1, :bar => 2
  end
end

Removing middleware

If you need to remove a middleware for some reason, you can do this in your configuration:

Sidekiq.configure_server do |config|
  config.server_middleware do |chain|
    chain.remove Some::Middleware
  end
end

Request-Specific Context

Sidekiq 6.3 adds support for serializing Rails' ActiveSupport::CurrentAttributes which ensures a job will have access to the same request-specific context as the HTTP request which created the job. See my blog post for details:

require "sidekiq/middleware/current_attributes"
Sidekiq::CurrentAttributes.persist(Myapp::Current) # Your AS::CurrentAttributes singleton, or...
Sidekiq::CurrentAttributes.persist("Myapp::Current") # initializers shouldn't load classes so we use the class name instead, or...
Sidekiq::CurrentAttributes.persist(["Myapp::Current", "Another::Current"]) # if you have multiple globals...

Middleware Ordering

Sidekiq will print out the configured client and server middleware chains when started with -v. Ordering can be critical if multiple middleware can conflict somehow. The chain class has the various APIs allowing you to adjust middleware ordering in your initializer.

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