rcmgr: warn if limits conflict with connmgr

[MarcoPolo]

We should emit some warning if the current limits conflict with the current settings for the connection manager.

Roughly:

• Look at the limits set by the resource manager if the resource manager is the default implementation provided by go-libp2p (the rcmgr interface doesn't allow us to see what the limits are)
• Look at the limits configured in the conn manager.
• The rcmgr conn limit should be higher than the high watermark of the conn manager. Log a warning if this isn't the case.

I think this makes sense to put in the connmgr code.

[piersy]

Hi @MarcoPolo, id be interested in picking this up, but I would need a bit of clarification from you about how you think this should work.

It looks to me like a good place to insert the check would be just after this block, since everything should have been configured by that point:

go-libp2p/config/config.go

Lines 297 to 302 in 4caa4e5

	func (cfg *Config) NewNode() (host.Host, error) {
	eventBus := eventbus.NewBus(eventbus.WithMetricsTracer(eventbus.NewMetricsTracer(eventbus.WithRegisterer(cfg.PrometheusRegisterer))))
	swrm, err := cfg.makeSwarm(eventBus, !cfg.DisableMetrics)
	if err != nil {
	return nil, err
	}

However the resource manager in rcmgr is not exported, were you planning on exporting it in order to get at the conn limit? The alternative I see would be to add a method to network.ResourceManager to expose the conn limit. Similarly were you planning on adding a method to connmgr.ConnManager to check the limit extracted from the resource manger?

Thanks!

[MarcoPolo]

Thanks @piersy!

Here's what I'm thinking:

1. We can do this at the start of the NewNode function since everything we need is in the Config.
2. The ConnManager can have a new method called CheckLimits(limits GetterConnLimits).
3. GetConnLimits is an interface with a single method GetConnLimits.
4. The private resourceManager type implements this interface and returns the total system limits.

Conn manager defines a new interface for the thing it checks its limits against. And the resourceManager implements this interface. The glue code in NewNode checks to see if the configured resource manager implements the interface and calls the CheckLimits method on the conn manager.

There's probably some subtleties here, but hopefully this is enough to get you started :)

[piersy]

Thanks @MarcoPolo, that sounds good to me!