DNS Reverse Lookup

The DNS processor performs reverse DNS lookups of IP addresses. It caches the responses that it receives in accordance to the time-to-live (TTL) value contained in the response. It also caches failures that occur during lookups. Each instance of this processor maintains its own independent cache.

The processor uses its own DNS resolver to send requests to nameservers and does not use the operating system’s resolver. It does not read any values contained in /etc/hosts.

This processor can significantly slow down your pipeline’s throughput if you have a high latency network or slow upstream nameserver. The cache will help with performance, but if the addresses being resolved have a high cardinality then the cache benefits will be diminished due to the high miss ratio.

By way of example, if each DNS lookup takes 2 milliseconds, the maximum throughput you can achieve is 500 events per second (1000 milliseconds / 2 milliseconds). If you have a high cache hit ratio then your throughput can be higher.

This is a minimal configuration example that resolves the IP addresses contained in two fields.

processors:
- dns:
    type: reverse
    fields:
      source.ip: source.hostname
      destination.ip: destination.hostname

Next is a configuration example showing all options.

processors:
- dns:
    type: reverse
    action: append
    fields:
      server.ip: server.hostname
      client.ip: client.hostname
    success_cache:
      capacity.initial: 1000
      capacity.max: 10000
    failure_cache:
      capacity.initial: 1000
      capacity.max: 10000
      ttl: 1m
    nameservers: ['192.0.2.1', '203.0.113.1']
    timeout: 500ms
    tag_on_failure: [_dns_reverse_lookup_failed]

The dns processor has the following configuration settings: