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Discovery via DNS

This module provides a service discovery mechanism that uses DNS to locate services. It supports both A/AAAA record resolution and SRV record resolution for service discovery.

DNS discovery can resolve services using:

  • A/AAAA records: Standard DNS address records that return IP addresses
  • SRV records: Service records that provide both IP addresses and port information

Enabling DNS Discovery Using Akka.Hosting

To enable DNS discovery using Akka.Hosting, you can use the WithDnsDiscovery extension method:

builder.WithDnsDiscovery();

For SRV record resolution, you also need to configure the async DNS resolver with custom nameservers:

builder.WithAsyncDnsResolver(opt => 
{
    opt.Nameservers = [  // at least one nameserver is required
        "127.0.0.1:1053", // IPv4 with port
        "[fd::aa:aa:aa:aa]", // IPv6 without port (default is 53)
        "1dot1dot1dot1.cloudflare-dns.com" // Hostname
    ];
});

Note: The default port for DNS is 53, so if you don't specify a port, it will use 53. DNS hostname would be resolved using the default System.Net.Dns.GetHostAddresses method.

Enabling DNS Discovery Using HOCON Configuration

To enable DNS discovery via HOCON, you will need to modify your HOCON configuration:

akka.discovery.method = dns

Below, you'll find the default configuration. It can be customized by changing these values in your HOCON configuration:

akka.discovery.dns {
    class = "Akka.Discovery.Dns.DnsServiceDiscovery, Akka.Discovery.Dns"
}

To enable async-dns resolver, you need to configure it in your HOCON configuration:

akka.io.dns.resolver = async-dns
akka.io.dns.async-dns {
    provider-object = "Akka.Discovery.Dns.Internal.AsyncDnsProvider, Akka.Discovery.Dns"
    nameservers = [ "127.0.0.1:53"; "my-dns.example.com"; "[::1]:53" ]
    cache-cleanup-interval = 120s
    positive-ttl = forever
  }

NOTES

  • async-dns resolver doesn't use System.Net.Dns.GetHostAddresses method to resolve DNS hostname, therefore it has no way to determine DNS nameserver from the runtime environment. You need to configure it explicitly.
  • async-dns resolver is required to resolve SRV records.
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