class Hoodoo::Services::Discovery::ByFlux

Discover resource endpoint locations via Alchemy Flux.

For Flux, it’s less about discovery as it is about convention and announcing. We have to set some system variables when the application starts up, before the Rack ‘run` call gets as far as the Alchemy Flux server’s implementation - in practice this means announcement needs to happen from the Hoodoo middleware’s constructor, synchronously. The environment variables tell Flux about this local service’s URI-located endpoints and derive a consistent, replicable ‘service name’ from the resources which the service implements.

Once all that is set up, the local Alchemy instance knows how to listen for relevant messages for ‘this’ service on the queue and Hoodoo in ‘this’ service knowns which resources are local, or which are remote; and it knows that Flux is able in turn to use URI-based to-resource communications for inter-resource calls without any further explicit discovery within Hoodoo beyond simply saying “here’s the AMQP Flux endpoint class”.

Protected Instance Methods

announce_remote( resource, version, options = {} ) click to toggle source

Announce the location of an instance to Alchemy Flux.

Call via Hoodoo::Services::Discovery::Base#announce.

resource: Passed to discover_remote.
version: Passed to discover_remote.
options: See below.

The Options hash informs the announcer of the intended endpoint base URI for the resource and also, where available, provides a head-up on the full range of resource names that will be present in this single service application (see Hoodoo::Services::Service::comprised_of). Keys MUST be Symbols. Associated required values are:

services: Array of Hoodoo::Services::Discovery::ForLocal instances describing available resources in this local service.

# File lib/hoodoo/services/discovery/discoverers/by_flux.rb, line 58
def announce_remote( resource, version, options = {} )

  alchemy_resource_paths = ENV[ 'ALCHEMY_RESOURCE_PATHS' ]
  alchemy_service_name   = ENV[ 'ALCHEMY_SERVICE_NAME'   ]

  # Under Flux, we "announce" via a local environment variable when
  # this service awakens which tells Flux what to listen for on the
  # AMQP queue.
  #
  # Since inbound HTTP calls into the architecture are based on URIs
  # and paths, there needs to be a mapping at that point to queue
  # endpoints. Historically Hoodoo adopted an (in hindsight, unwise)
  # approach of "/v<version>/<pluralised_resource>" c.f. Rails,
  # rather than just "/<version>/<resource>" - e.g. there was
  # "/v1/members" instead of "/1/Member". This means things like the
  # "ByConvention" discoverer have to use pluralisation rules and
  # exceptions. It's messy.
  #
  # To clean things up, the work on Alchemy Flux sets up *two* paths
  # in Hoodoo - the old one for backwards compatibility, and a new
  # one of the above simpler form. Now it's easy to go from version
  # and resource name to path or back internally with no mappings.
  #
  if ( alchemy_resource_paths.nil? ||
       alchemy_resource_paths.strip.empty? )

    services = options[ :services ] || []
    paths    = []

    services.each do | service |
      custom_path   = service.base_path
      de_facto_path = service.de_facto_base_path

      paths << custom_path << de_facto_path
    end

    ENV[ 'ALCHEMY_RESOURCE_PATHS' ] = paths.join( ',' )
  end

  if ( alchemy_service_name.nil? ||
       alchemy_service_name.strip.empty? )
    ENV[ 'ALCHEMY_SERVICE_NAME' ] = Hoodoo::Services::Middleware::service_name()
  end

  return discover_remote( resource, version )
end

discover_remote( resource, version ) click to toggle source

Discover the location of an instance.

Returns a Hoodoo::Services::Discovery::ForAMQP instance if the endpoint is found, else nil.

Call via Hoodoo::Services::Discovery::Base#announce.

resource: Passed to discover_remote.
version: Passed to discover_remote.

# File lib/hoodoo/services/discovery/discoverers/by_flux.rb, line 115
def discover_remote( resource, version )
  de_facto_path = Hoodoo::Services::Middleware::de_facto_path_for(
    resource,
    version
  )

  return Hoodoo::Services::Discovery::ForAMQP.new(
    resource: resource,
    version:  version
  )
end