record_transformer
The filter_record_transformer
filter plugin mutates/transforms incoming event streams in a versatile manner. If there is a need to add/delete/modify events, this plugin is the first filter to try.
It is included in the Fluentd's core.
Example Configurations
The above filter adds the new field hostname
with the server's hostname as its value (It is taking advantage of Ruby's string interpolation) and the new field tag
with tag value.
So, an input like:
is transformed into
Here is another example where the field total
is divided by the field count
to create a new field avg
:
It transforms an event like
into
With the enable_ruby
option, an arbitrary Ruby expression can be used inside ${...}
. Note that the avg
field is typed as a string in this example. You may use auto_typecast true
option to treat the field as a float.
You can also use this plugin to modify your existing fields as:
An input like
is transformed into
Finally, this configuration embeds the value of the second part of the tag in the field service_name
. It might come in handy when aggregating data across many services.
So, if an event with the tag web.auth
and record {"user_id":1, "status":"ok"}
comes in, it transforms it into {"user_id":1, "status":"ok", "service_name":"auth"}
.
Parameters
See Common Parameters.
@type
@type
The value must be record_transformer
.
<record>
directive
<record>
directiveThe parameters inside <record>
directives are considered to be new key-value pairs:
For NEW_FIELD
and NEW_VALUE
, a special syntax ${}
allows the user to generate a new field dynamically. Inside the curly braces, the following variables are available:
The incoming event's existing values can be referred by their field
names. So, if the record is
{"total":100, "count":10}
, thenrecord["total"]=100
andrecord["count"]=10
.tag
refers to the whole tag.time
refers to stringified event time.hostname
refers to the machine's hostname. The actual value is the result of
You can also access to a certain portion of a tag using the following notations:
tag_parts[N]
refers to theNth
part of the tag.tag_prefix[N]
refers to the[0..N]
part of the tag.tag_suffix[N]
refers to the[N..]
part of the tag.
All indices are zero-based. For example, if you have an incoming event tagged debug.my.app
, then tag_parts[1]
will represent my
. Also in this case, tag_prefix[N]
and tag_suffix[N]
will work as follows:
enable_ruby
enable_ruby
When set to true
, the full Ruby syntax is enabled in the ${...}
expression. The default value is false
.
With true
, additional variables could be used inside ${}
:
record
refers to the whole record.time
refers to event time as Time object, not stringified event time.
Here is an example:
By historical reason, enable_ruby true
is too slow. If you need this option, consider record_modifier
filter instead. See also Need more performance?
section.
auto_typecast
auto_typecast
Automatically casts the field types. Default is false
.
LIMITATION: This option is effective only for field values comprised of a single placeholder.
Effective examples:
Non-Effective examples:
Internally, this keeps the original value type only when a single placeholder is used.
renew_record
renew_record
By default, the record transformer filter mutates the incoming data. However, if this parameter is set to true
, it modifies a new empty hash instead.
renew_time_key
renew_time_key
renew_time_key foo
overwrites the time of events with a value of the record field foo
if exists. The value of foo
must be a Unix timestamp.
keep_keys
keep_keys
A list of keys to keep. Only relevant if renew_record
is set to true
.
keep_keys
has been supported since 0.14.0.
remove_keys
remove_keys
A list of keys to delete.
This parameter supports nested field via record_accessor syntax since v1.1.0.
Example:
Given the configuration:
And a message:
The output would be:
Need more performance?
filter_record_modifier
is lightweight and faster version of filter_record_transformer
. filter_record_modifier
does not provide several filter_record_transformer
features, but it covers popular cases. If you need better performance for mutating records, consider filter_record_modifier
instead.
Tips
Use dig
Method for Nested Field
dig
Method for Nested FieldUsers sometimes need to access a nested field. In this case, you can use []
to create a chain like this:
But, this approach has a problem. When record["top"]
or record["top"]["nest1"]
does not exist, you hit an unexpected error.
Here is the log example:
dig
method resolves this problem. If field is not found, it returns nil
instead of raising error:
FAQ
What are the differences between ${record["key"]}
and ${key}
?
${record["key"]}
and ${key}
?${key}
was a shortcut for ${record["key"]}
. This is error-prone because ${tag}
is unclear, event tag or record["tag"]
. So the ${key}
syntax was removed since v0.14. v0.12 still supports ${key}
but it is not recommended.
I got unknown placeholder ${record['msg']} found
error, why?
unknown placeholder ${record['msg']} found
error, why?Without enable_ruby
, ${}
placeholder supports only double-quoted string for record field access. So, use ${record["key"]}
instead of ${record['key']}
. This could also happen when the input does not contain key
.
Learn More
If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is an open-source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.
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