Load Balancing Options all for rfc2136 provider

[marbon87]

We have to update multiple dns-servers with the same records and actually using multiple external-dns applications with the rfc2136 provider (one per destination) to update all dns-servers.

rfc2136 provider allows to configure multiple hosts to be update but only with the load balancing strategy round-robin, random and disabled.
I would be helplful to have a load balancing option "all" that updates all configred hosts.

[Jeremy-Boyle]

Hi @marbon87 what would you be looking to achieve here ?

Sending the records to all the hosts at once, that way if you have segmented hosts which do not update each other such as a dns farm?

I think the issue might be if one of them is down then that might cause a issue with the current code, but thats easily fixable.

[marbon87]

Exactly, I want to update all hosts simultaneously.

[Jeremy-Boyle]

Actually, looking at the code, I believe this behavior is already implemented. Load balancing is handled with the flag as you mentioned, and if multiple nameservers are defined, it will cycle through them as expected. The documentation could be clearer, but typically, load balancing is meant for distributing requests across multiple targets. Explicitly adding an "all" option doesn’t align with the conventional definition of load balancing. By default defining more than one host behaves in the manor you are looking for with the existing code in main. Could you please confirm it works as you would expect ?

Please take a look:

external-dns/provider/rfc2136/rfc2136.go

Lines 587 to 616 in 3f8cef2

	for i := 0; i < len(r.nameservers); i++ {
	nameserver := r.getNextNameserver()
	log.Debugf("Sending message to nameserver: %s", nameserver)
	c, err := makeClient(r, nameserver)
	if err != nil {
	lastErr = fmt.Errorf("error setting up TLS: %w", err)
	r.lastErr = lastErr
	continue
	}
	if !r.insecure {
	if r.gssTsig {
	keyName, handle, err := r.KeyData(nameserver)
	if err != nil {
	lastErr = err
	r.lastErr = lastErr
	continue
	}
	defer handle.Close()
	defer handle.DeleteContext(keyName)
	c.TsigProvider = handle
	msg.SetTsig(keyName, tsig.GSS, clockSkew, time.Now().Unix())
	} else {
	c.TsigProvider = tsig.HMAC{r.tsigKeyName: r.tsigSecret}
	msg.SetTsig(r.tsigKeyName, r.tsigSecretAlg, clockSkew, time.Now().Unix())
	}
	}

external-dns/provider/rfc2136/rfc2136.go

Lines 539 to 577 in 3f8cef2

	func (r *rfc2136Provider) getNextNameserver() string {
	if len(r.nameservers) == 1 {
	return r.nameservers[0]
	}
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.lastErr != nil {
	log.Warnf("Last operation failed for nameserver %s", r.nameservers[r.counter])
	log.Warnf("Last operation error message: %v", r.lastErr)
	}
	var nameserver string
	switch r.loadBalancingStrategy {
	case "random":
	for {
	nameserver = r.nameservers[r.randGen.Intn(len(r.nameservers))]
	// Ensure that we don't get the same nameserver as the last one
	if nameserver != r.nameservers[r.counter] {
	break
	}
	}
	case "round-robin":
	nameserver = r.nameservers[r.counter]
	r.counter = (r.counter + 1) % len(r.nameservers)
	default:
	if r.lastErr != nil {
	r.counter = (r.counter + 1) % len(r.nameservers)
	nameserver = r.nameservers[r.counter]
	} else {
	nameserver = r.nameservers[r.counter]
	}
	}
	// Last error has been logged, reset it for the next operation
	r.lastErr = nil
	return nameserver
	}