Transport

class oslo_messaging.Transport(driver)

A messaging transport.

This is a mostly opaque handle for an underlying messaging transport driver.

RPCs and Notifications may use separate messaging systems that utilize different drivers, access permissions, message delivery, etc. To ensure the correct messaging functionality, the corresponding method should be used to construct a Transport object from transport configuration gleaned from the user’s configuration and, optionally, a transport URL.

The factory method for RPC Transport objects:

def get_rpc_transport(conf, url=None,
                      allowed_remote_exmods=None)

If a transport URL is supplied as a parameter, any transport configuration contained in it takes precedence. If no transport URL is supplied, but there is a transport URL supplied in the user’s configuration then that URL will take the place of the URL parameter.

The factory method for Notification Transport objects:

def get_notification_transport(conf, url=None,
                               allowed_remote_exmods=None)

If no transport URL is provided, the URL in the notifications section of the config file will be used. If that URL is also absent, the same transport as specified in the user’s default section will be used.

The Transport has a single ‘conf’ property which is the cfg.ConfigOpts instance used to construct the transport object.

class oslo_messaging.TransportURL(conf, transport=None, virtual_host=None, hosts=None, aliases=None, query=None)

A parsed transport URL.

Transport URLs take the form:

transport://user:pass@host:port[,userN:passN@hostN:portN]/virtual_host?query

i.e. the scheme selects the transport driver, you may include multiple hosts in netloc, the path part is a “virtual host” partition path and the query part contains some driver-specific options which may override corresponding values from a static configuration.

Parameters:
  • conf (oslo.config.cfg.ConfigOpts) – a ConfigOpts instance
  • transport (str) – a transport name for example ‘rabbit’
  • virtual_host (str) – a virtual host path for example ‘/’
  • hosts (list) – a list of TransportHost objects
  • aliases (dict) – DEPRECATED: a map of transport alias to transport name
  • query (dict) – a dictionary of URL query parameters
classmethod parse(conf, url=None, aliases=None)

Parse an url.

Assuming a URL takes the form of:

transport://user:pass@host:port[,userN:passN@hostN:portN]/virtual_host?query

then parse the URL and return a TransportURL object.

Netloc is parsed following the sequence bellow:

  • It is first split by ‘,’ in order to support multiple hosts

  • All hosts should be specified with username/password or not at the same time. In case of lack of specification, username and password will be omitted:

    user:pass@host1:port1,host2:port2

[
  {"username": "user", "password": "pass", "host": "host1:port1"},
  {"host": "host2:port2"}
]

If the url is not provided conf.transport_url is parsed instead.

Parameters:
  • conf (oslo.config.cfg.ConfigOpts) – a ConfigOpts instance
  • url (str) – The URL to parse
  • aliases (dict) – A map of transport alias to transport name
Returns:

A TransportURL
class oslo_messaging.TransportHost(hostname=None, port=None, username=None, password=None)

A host element of a parsed transport URL.

oslo_messaging.set_transport_defaults(control_exchange)

Set defaults for messaging transport configuration options.

Parameters:control_exchange (str) – the default exchange under which topics are scoped

Forking Processes and oslo.messaging Transport objects

oslo.messaging can’t ensure that forking a process that shares the same transport object is safe for the library consumer, because it relies on different 3rd party libraries that don’t ensure that. In certain cases, with some drivers, it does work:

  • rabbit: works only if no connection have already been established.
  • amqp1: works