Let user specify network name for autoscaling in Docker Swarm

[vicary]

Make sure you read and understand http://emqtt.io/docs/v2/index.html.
Use one of the two templates below and delete the rest.

• BUG REPORT
• FEATURE REQUEST

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FEATURE REQUEST

Missing feature

Able to specify a network interface in env var, then start.sh or cluster.sh uses the specified network to resolve the default IP into $LOCAL_IP.

devOps should be able to dynamically allocate EMQ_HOST or EMQ_NODE__NAME in a deterministic way, since Docker services with multiple networks will attach interfaces in random order.

Justification

With multiple networks attached, the current way to get LOCAL_IP in start.sh is not deterministic; While IP is generated after the container is spawn.

Workarounds

Are there any workarounds you currently have in place because the feature is missing?

In short, no.

The overlay network address is load balanced and cannot resolve single nodes, individual nodes spawned need a way to resolve their own unique address correctly, especially when there are more than one interface and/or IP available.

[ozbillwang]

@vicary

Did you get any solution on it?

The exist solution to join cluster, doesn't really work.

For example, I have aws load balancer,

DNS (q.mqtt.com) -> aws elb (8883) -> ssl offload |-> node1 (1883)
                                                  |-> node2 (1883)

What cluster should I join? DNS name, elb end point, or others?

Second, the note for cluster

Note: You must publsh port 4369 and range of port 6000-6999 for EMQ Clustered.

So does it mean I have to open multiple port , 4369 and 6000-6999 on elb ? Currently aws elb doesn't support to listen multiple ports. I have to set the port redirection one by one

[vicary]

@ozbillwang Not sure if you're spawning them in docker swarm. If so, ELB may not be able to route inside the swarm ingress network. You could either use host networking for your containers, or spin up something like Traefik to route external connections from ELB to container IP's or service networks.