IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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Dns filter plugin

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Dns filter plugin

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Plugin version: v3.2.0
Released on: 2023-01-26
Changelog

For other versions, see the Versioned plugin docs.

Getting Help

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For questions about the plugin, open a topic in the Discuss forums. For bugs or feature requests, open an issue in Github. For the list of Elastic supported plugins, please consult the Elastic Support Matrix.

Description

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The DNS filter performs a lookup (either an A record/CNAME record lookup or a reverse lookup at the PTR record) on records specified under the reverse arrays or respectively under the resolve arrays.

The config should look like this:

    filter {
      dns {
        reverse => [ "source_host", "field_with_address" ]
        resolve => [ "field_with_fqdn" ]
        action => "replace"
      }
    }

This filter, like all filters, only processes 1 event at a time, so the use of this plugin can significantly slow down your pipeline’s throughput if you have a high latency network. By way of example, if each DNS lookup takes 2 milliseconds, the maximum throughput you can achieve with a single filter worker is 500 events per second (1000 milliseconds / 2 milliseconds).

Dns Filter Configuration Options

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This plugin supports the following configuration options plus the Common Options described later.

Setting	Input type	Required
`action`	string, one of `["append", "replace"]`	No
`failed_cache_size`	number	No
`failed_cache_ttl`	number	No
`hit_cache_size`	number	No
`hit_cache_ttl`	number	No
`hostsfile`	array	No
`max_retries`	number	No
`nameserver`	hash	No
`resolve`	array	No
`reverse`	array	No
`tag_on_timeout`	array	No
`timeout`	number	No

Also see Common Options for a list of options supported by all filter plugins.

`action`

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Value can be any of: append, replace
Default value is "append"

Determine what action to do: append or replace the values in the fields specified under reverse and resolve.

`failed_cache_size`

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Value type is number
Default value is 0 (cache disabled)

cache size for failed requests

`failed_cache_ttl`

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Value type is number
Default value is 5

how long to cache failed requests (in seconds)

`hit_cache_size`

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Value type is number
Default value is 0 (cache disabled)

set the size of cache for successful requests

`hit_cache_ttl`

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Value type is number
Default value is 60

how long to cache successful requests (in seconds)

`hostsfile`

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Value type is array
There is no default value for this setting.

Use custom hosts file(s). For example: ["/var/db/my_custom_hosts"]

`max_retries`

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Value type is number
Default value is 2

number of times to retry a failed resolve/reverse

`nameserver`

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Value type is hash, and is composed of:
- a required address key, whose value is either a string or an array, representing one or more nameserver ip addresses
- an optional search key, whose value is either a string or an array, representing between one and six search domains (e.g., with search domain com, a query for example will match DNS entries for example.com)
- an optional ndots key, used in conjunction with search, whose value is a number, representing the minimum number of dots in a domain name being resolved that will prevent the search domains from being used (default 1; this option is rarely needed)
For backward-compatibility, values of string and array are also accepted, representing one or more nameserver ip addresses without search domains.
There is no default value for this setting.

Use custom nameserver(s). For example:

    filter {
      dns {
        nameserver => {
          address => ["8.8.8.8", "8.8.4.4"]
          search  => ["internal.net"]
        }
      }
    }

If nameserver is not specified then /etc/resolv.conf will be read to configure the resolver using the nameserver, domain, search and ndots directives in /etc/resolv.conf.

`resolve`

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Value type is array
There is no default value for this setting.

Forward resolve one or more fields.

`reverse`

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Value type is array
There is no default value for this setting.

Reverse resolve one or more fields.

`timeout`

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Value type is number
Default value is 0.5

resolv calls will be wrapped in a timeout instance

`tag_on_timeout`

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Value type is array
Defaults to ["_dnstimeout"].

Add tag(s) on DNS lookup time out.

Common Options

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The following configuration options are supported by all filter plugins:

Setting	Input type	Required
`add_field`	hash	No
`add_tag`	array	No
`enable_metric`	boolean	No
`id`	string	No
`periodic_flush`	boolean	No
`remove_field`	array	No
`remove_tag`	array	No

`add_field`

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Value type is hash
Default value is {}

If this filter is successful, add any arbitrary fields to this event. Field names can be dynamic and include parts of the event using the %{field}.

Example:

    filter {
      dns {
        add_field => { "foo_%{somefield}" => "Hello world, from %{host}" }
      }
    }

    # You can also add multiple fields at once:
    filter {
      dns {
        add_field => {
          "foo_%{somefield}" => "Hello world, from %{host}"
          "new_field" => "new_static_value"
        }
      }
    }

If the event has field "somefield" == "hello" this filter, on success, would add field foo_hello if it is present, with the value above and the %{host} piece replaced with that value from the event. The second example would also add a hardcoded field.

`add_tag`

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Value type is array
Default value is []

If this filter is successful, add arbitrary tags to the event. Tags can be dynamic and include parts of the event using the %{field} syntax.

Example:

    filter {
      dns {
        add_tag => [ "foo_%{somefield}" ]
      }
    }

    # You can also add multiple tags at once:
    filter {
      dns {
        add_tag => [ "foo_%{somefield}", "taggedy_tag"]
      }
    }

If the event has field "somefield" == "hello" this filter, on success, would add a tag foo_hello (and the second example would of course add a taggedy_tag tag).

`enable_metric`

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Value type is boolean
Default value is true

Disable or enable metric logging for this specific plugin instance. By default we record all the metrics we can, but you can disable metrics collection for a specific plugin.

`id`

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Value type is string
There is no default value for this setting.

Add a unique ID to the plugin configuration. If no ID is specified, Logstash will generate one. It is strongly recommended to set this ID in your configuration. This is particularly useful when you have two or more plugins of the same type, for example, if you have 2 dns filters. Adding a named ID in this case will help in monitoring Logstash when using the monitoring APIs.

    filter {
      dns {
        id => "ABC"
      }
    }

Variable substitution in the id field only supports environment variables and does not support the use of values from the secret store.

`periodic_flush`

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Value type is boolean
Default value is false

Call the filter flush method at regular interval. Optional.

`remove_field`

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Value type is array
Default value is []

If this filter is successful, remove arbitrary fields from this event. Fields names can be dynamic and include parts of the event using the %{field} Example:

    filter {
      dns {
        remove_field => [ "foo_%{somefield}" ]
      }
    }

    # You can also remove multiple fields at once:
    filter {
      dns {
        remove_field => [ "foo_%{somefield}", "my_extraneous_field" ]
      }
    }

If the event has field "somefield" == "hello" this filter, on success, would remove the field with name foo_hello if it is present. The second example would remove an additional, non-dynamic field.

`remove_tag`

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Value type is array
Default value is []

If this filter is successful, remove arbitrary tags from the event. Tags can be dynamic and include parts of the event using the %{field} syntax.

Example:

    filter {
      dns {
        remove_tag => [ "foo_%{somefield}" ]
      }
    }

    # You can also remove multiple tags at once:
    filter {
      dns {
        remove_tag => [ "foo_%{somefield}", "sad_unwanted_tag"]
      }
    }

If the event has field "somefield" == "hello" this filter, on success, would remove the tag foo_hello if it is present. The second example would remove a sad, unwanted tag as well.

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