Open Stack

> My opinion is that we create a *new* transport client instance for every
service client, not re-use existing instances. What’s your take on this?

I'm not in agreement and here is why (with a use case).

A transport client is concerned with transporting only. Whether the same
one is used for each service or a new one is used for each service doesn't
matter.

An example of using two transport clients would be a case where an
application communicates with two different OpenStack clouds. One is a
public cloud and the application communicates through a proxy. A transport
client would know how to talk through the proxy to the public cloud. A
second OpenStack cloud is a private cloud that is on the same company
network. A second transport client would know how to talk to that without
communicating through the proxy.

The service clients communicating with each cloud would use the appropriate
transport client.

The mapping of transport client to service client doesn't need to be 1:1 if
they operate in different spaces. Only having instances of a transport
client as needed decreases the use of resources or the time needed to
manage those.

If a transport client is only concerned with transporting than what is the
need to have more than one per case to transport?

- Matt

On Thu, Jun 5, 2014 at 12:09 PM, Jamie Hannaford <
jamie.hannaford at rackspace.com> wrote:

>  I completely agree with you regarding separation of concerns.
>
>  I also agree with your definitions: a transport client is for managing
> HTTP transactions, a service client contains all the domain logic for an
> API service (Swift, Nova, etc.). A service knows nothing about HTTP, a
> transport client knows nothing about Swift. A transport client is injected
> into the service client, satisfying the type hint. So any transport client
> implementing our interface is fine.
>
>  Up to this point I’m in 100% agreement. The area which I think I
> misunderstood was the *creation process* of service clients. My take was
> that you were advocating a shared transport client instance - i.e. a
> transport client instantiated once, and re-used for every service client.
> If we did that, there would be global state.
>
>  My opinion is that we create a *new* transport client instance for every
> service client, not re-use existing instances. What’s your take on this?
>
>  Jamie
>
> On June 5, 2014 at 5:17:57 PM, Matthew Farina (matt at mattfarina.com) wrote:
>
>  We've started to talk about the interactions between transport
> clients, service clients, and state. I've noticed we're not on the
> same page so I wanted to start a dialog. Here's my starting point...
>
> A Transport Client is about transporting data. It sends and receives data.
>
> A Service Client handles the interactions with a service (e.g., swift,
> nova, keystone).
>
> A Service Client uses a Transport Client when it needs to transport
> data to and from a service.
>
> When it comes to state, a Transport Client knows about transporting
> things. That means it knows things like if there is a proxy and how to
> work with it. A Service Client knows about a service which includes
> and state for that service.
>
> In the realm of separation of concerns, a Service Client doesn't know
> about transport state and a Transport Client doesn't know about
> service state. They are separate.
>
> A Service Client doesn't care what Transport Client is used as long as
> the API (interface) is compliant. A Transport Client doesn't care what
> code calls it as long as it uses the public API defined by an
> interface.
>
> This is my take. If someone has a different take please share it with
> the reasoning.
>
> - Matt
>
>
>
>   Jamie Hannaford
> Software Developer III - CH [image: experience Fanatical Support] [image:
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