public SELF cacheSpec(String cacheSpec) {
        requireNonNull(cacheSpec, "cacheSpec");
        this.cacheSpec = cacheSpec;
        needsToCreateDnsCache = true;
        return self();
    }
Sets the {@linkplain CaffeineSpec Caffeine specification string} of the cache that stores the domain
names and their resolved addresses. If not set, {@link Flags#dnsCacheSpec()} is used by default.

<p>Note that {@link #cacheSpec(String)} and {@link #dnsCache(DnsCache)} are mutually exclusive.
core/src/main/java/com/linecorp/armeria/client/AbstractDnsResolverBuilder.java