dns-load-balancer

Forward DNS queries to DNS-servers. Sometimes I need to access a kubernetes-cluster using a wireguard vpn-tunnel and access some services. So I usually let wireguard define the DNS-server I am using since it also resolve to public DNS besides the internal kubernetes-services.

Sometimes the vpn-tunnel becomes stale and I need to disconnect and reconnect. So I wanted a DNS-forwarder that could talk to one or more public DNS-servers besides the kubernetes DNS-server. I started out having Claude make a simpel DNS-forwarder.

During the development I wanted to use tokio for asynchronous tasks. Claude have done the heavy lifting.

This DNS-forwarder will send out a request to each DNS-server defined in config.rs and stop when it receives an answer or None if name resolution was not successful.

I noticed a delay when connecting to a kubernetes-service and it turned out the client was issuing a DNS-request for type A (IPv4), AAAA (IPv6) and that introduced this delay. The client in this case is psql to access a PostgreSQL database.

So a check is added that if the request is for a cluster.local. any request other than a type A will be ignored.

Clone, build and run the project with

cargo build [--release]
sudo ./target/[debug|release]/dns_load_balancer run --config [CONFIG]

Install via brew tap.

brew tap kometen/dns-load-balancer
brew install dns-load-balancer

An example of a configuration is printed to the console with ./target/release/dns_load_balancer example. Save end edit the file config.toml to use your preferred DNS-servers.

Since it connects to port 53 you need priviliged access for it to start.

As an example here is my config.toml:

$ cat /usr/local/etc/dns-load-balancer/config.toml
[[servers]]
address = "1.1.1.1"
use_tls = true
description = "Cloudflare DNS"

[[servers]]
address = "8.8.8.8"
use_tls = true
description = "Google DNS"

[[servers]]
address = "10.152.183.10"
use_tls = false
description = "Kubernetes DNS"

And when Wireguard VPN-tunnel is not connected to Kubernetes DNS:

$ host postgresql.invoice.svc.cluster.local
DNS resolution failed: Failed to resolve hostname: postgresql.invoice.svc.cluster.local.
Root cause: no record found for Query { name: Name("postgresql.invoice.svc.cluster.local."), query_type: AAAA, query_class: IN }
Error: Failed to resolve hostname: postgresql.invoice.svc.cluster.local.

Caused by:
    no record found for Query { name: Name("postgresql.invoice.svc.cluster.local."), query_type: AAAA, query_class: IN }

When connected:

$ host postgresql.invoice.svc.cluster.local
postgresql.invoice.svc.cluster.local has address 10.152.183.95

Had I configured the Kubernetes DNS as the only DNS-server, either in network-settings or in config.toml no nameresolution would take place. By adding Cloudflare and Google nameresolution will usually work and only fail if the Wireguard VPN is not connected and I query for services in Kubernetes.