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:

type
The type of DNS lookup to perform. The only supported type is reverse which queries for a PTR record.
action
This defines the behavior of the processor when the target field already exists in the event. The options are append (default) and replace.
fields
This is a mapping of source field names to target field names. The value of the source field will be used in the DNS query and result will be written to the target field.
success_cache.capacity.initial
The initial number of items that the success cache will be allocated to hold. When initialized the processor will allocate the memory for this number of items. Default value is 1000.
success_cache.capacity.max
The maximum number of items that the success cache can hold. When the maximum capacity is reached a random item is evicted. Default value is 10000.
failure_cache.capacity.initial
The initial number of items that the failure cache will be allocated to hold. When initialized the processor will allocate the memory for this number of items. Default value is 1000.
failure_cache.capacity.max
The maximum number of items that the failure cache can hold. When the maximum capacity is reached a random item is evicted. Default value is 10000.
failure_cache.ttl
The duration for which failures are cached. Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h". Default value is 1m.
nameservers
A list of nameservers to query. If there are multiple servers, the resolver queries them in the order listed. If none are specified then it will read the nameservers listed in /etc/resolv.conf once at initialization. On Windows you must always supply at least one nameserver.
timeout
The duration after which a DNS query will timeout. This is timeout for each DNS request so if you have 2 nameservers then the total timeout will be 2 times this value. Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h". Default value is 500ms.
tag_on_failure
A list of tags to add to the event when any lookup fails. The tags are only added once even if multiple lookups fail. By default no tags are added upon failure.