private static HttpResponse addViaHeader(HttpResponse res) {
        return res.mapHeaders(headers -> headers.toBuilder()
                                                .add(HttpHeaderNames.VIA, viaHeaderValue)
                                                .build());
    }
We used hardcoded backend addresses. But you can use other service discovery mechanisms to configure
backends dynamically using {@link DnsServiceEndpointGroup}, ZooKeeper or Central Dogma.
See <a href="https://armeria.dev/docs/client-service-discovery">service discovery</a>,
<a href="https://armeria.dev/docs/advanced-zookeeper">Service discovery
with ZooKeeper</a> and <a href="https://line.github.io/centraldogma/">centraldogma</a>.
examples/proxy-server/src/main/java/example/armeria/proxy/ProxyService.java