require explicitly specifying node name in subscription pubsub

[azhi]

modify pubsub behaviour to include node_name/0 callback

Justification for breaking change

Currently pubsub system (specifically pubsub proxy server) relies on Kernel.node/0 to check whether message is local or not. Kernel.node is a function that was intended to work inside erlang cluster.

But pubsub system can be run in a "cluster" connected through a bunch of mechanisms, not only in erlang cluster. Phoenix pubsub recognizes this and includes a node_name function in it's specification, which is used in different pubsub adapters, such as redis one, where you could explicitly specify node name.

In fact, this is the background for this PR - I was using redis adapter, and couldn't make subscriptions work. Turns out it was because of this node names issue. It could be fixed by switching from using explicit node_name in Phoenix.PubSub.Redis config to using --sname flag, but I think it is worth fixing now when not a lot of people is dependent on current Absinthe.Subscription.Pubsub.

[benwilson512]

Hey @azhi I appreciate the PR! We're gonna be reconfiguring the whole internals of PubSub for 1.5 probably, so I my hold off on merging this for a while so I can evaluate it in that context.

[azhi]

Oh, ok, I guess I'll have to revisit all this stuff when upgrading to 1.5 :).

I was also gonna make some work in supporting Direct usage of phoenix pubsub in absinthe_phoenix. Do you want me to open PR for that, or this part will also be reworked in 1.5?

[benwilson512]

Thanks!

[benwilson512]

@azhi by all means do a PR for direct usage. I'm hoping we wouldn't have to change very much but please go for it!