Reduce transform

Collapse multiple log events into a single event based on a set of conditions and merge strategies

Reduces multiple log events into a single log event based on a set of conditions and merge strategies.

Configuration

Example configurations

{
  "transforms": {
    "my_transform_id": {
      "type": "reduce",
      "inputs": [
        "my-source-or-transform-id"
      ]
    }
  }
}

[transforms.my_transform_id]
type = "reduce"
inputs = [ "my-source-or-transform-id" ]

transforms:
  my_transform_id:
    type: reduce
    inputs:
      - my-source-or-transform-id

{
  "transforms": {
    "my_transform_id": {
      "type": "reduce",
      "inputs": [
        "my-source-or-transform-id"
      ],
      "expire_after_ms": 30000,
      "flush_period_ms": 1000,
      "group_by": [
        "request_id"
      ]
    }
  }
}

[transforms.my_transform_id]
type = "reduce"
inputs = [ "my-source-or-transform-id" ]
expire_after_ms = 30_000
flush_period_ms = 1_000
group_by = [ "request_id" ]

transforms:
  my_transform_id:
    type: reduce
    inputs:
      - my-source-or-transform-id
    expire_after_ms: 30000
    flush_period_ms: 1000
    group_by:
      - request_id

end_every_period_ms

optional uint

If supplied, every time this interval elapses for a given grouping, the reduced value for that grouping is flushed. Checked every flush_period_ms.

ends_when

optional condition

A condition used to distinguish the final event of a transaction.

If this condition resolves to true for an event, the current transaction is immediately flushed with this event.

ends_when.source

The text of the condition. The syntax of the condition depends on the value of type.

ends_when.type

The type of condition to supply. See Available syntaxes below for a list of available types for this transform.

Available syntaxes

Syntax	Description	Example
`vrl`	A Vector Remap Language (VRL) Boolean expression.	`.status_code != 200 && !includes(["info", "debug"], .severity)`
`datadog_search`	A Datadog Search query string.	`*stack`
`is_log`	Whether the incoming event is a log.
`is_metric`	Whether the incoming event is a metric.
`is_trace`	Whether the incoming event is a trace.

Shorthand for VRL

If you opt for the vrl syntax for this condition, you can set the condition as a string via the condition parameter, without needing to specify both a source and a type. The table below shows some examples:

Config format	Example
YAML	`condition: .status == 200`
TOML	`condition = ".status == 200"`
JSON	`"condition": ".status == 200"`

Condition config examples

Standard VRL

ends_when:
  type: "vrl"
  source: ".status == 500"

ends_when = { type = "vrl", source = ".status == 500" }

"ends_when": {
  "type": "vrl",
  "source": ".status == 500"
}

Datadog Search

ends_when:
  type: "datadog_search"
  source: "*stack"

ends_when = { type = "datadog_search", source = "*stack" }

"ends_when": {
  "type": "datadog_search",
  "source": "*stack"
}

VRL shorthand

ends_when: ".status == 500"

ends_when = ".status == 500"

"ends_when": ".status == 500"

expire_after_ms

optional uint

The maximum period of time to wait after the last event is received, in milliseconds, before a combined event should be considered complete.

default: 30000(milliseconds)

flush_period_ms

optional uint

The interval to check for and flush any expired events, in milliseconds.

default: 1000(milliseconds)

graph

optional object

Extra graph configuration

Configure output for component when generated with graph command

graph.node_attributes

optional object

Node attributes to add to this component’s node in resulting graph

They are added to the node as provided

graph.node_attributes.*

required string literal

A single graph node attribute in graphviz DOT language.

Examples

{
  "color": "red",
  "name": "Example Node",
  "width": "5.0"
}

group_by

optional [string]

An ordered list of fields by which to group events.

Each group with matching values for the specified keys is reduced independently, allowing you to keep independent event streams separate. Note that each field specified, will be reduced with the default merge strategy based on its type unless a merge strategy is explicitly defined in merge_strategies.

This field is optional and when not specified, all events are reduced in a single group.

For example, if group_by = ["host", "region"], then all incoming events that have the same host and region are grouped together before being reduced.

Array string literal

Examples

[
  "request_id",
  "user_id",
  "transaction_id"
]

inputs

required [string]

A list of upstream source or transform IDs.

Wildcards (*) are supported.

See configuration for more info.

Array string literal

Examples

[
  "my-source-or-transform-id",
  "prefix-*"
]

max_events

optional uint

The maximum number of events to group together.

merge_strategies

optional object

A map of field names to custom merge strategies.

For each field specified, the given strategy is used for combining events rather than the default behavior.

The default behavior is as follows:

The first value of a string field is kept and subsequent values are discarded.
For timestamp fields the first is kept and a new field [field-name]_end is added with the last received timestamp value.
Numeric values are summed.
For nested paths, the field value is retrieved and then reduced using the default strategies mentioned above (unless explicitly specified otherwise).

merge_strategies.*

required string literal enum

An individual merge strategy.

Enum options

Option	Description
`array`	Append each value to an array.
`concat`	Concatenate each string value, delimited with a space.
`concat_newline`	Concatenate each string value, delimited with a newline.
`concat_raw`	Concatenate each string, without a delimiter.
`discard`	Discard all but the first value found.
`flat_unique`	Create a flattened array of all unique values.
`longest_array`	Keep the longest array seen.
`max`	Keep the maximum numeric value seen.
`min`	Keep the minimum numeric value seen.
`retain`	Discard all but the last value found. Works as a way to coalesce by not retaining `null`.
`shortest_array`	Keep the shortest array seen.
`sum`	Sum all numeric values.

Examples

"array"

"concat"

"concat_newline"

"concat_raw"

"discard"

"flat_unique"

"longest_array"

"max"

"min"

"retain"

"shortest_array"

"sum"

starts_when

optional condition

A condition used to distinguish the first event of a transaction.

If this condition resolves to true for an event, the previous transaction is flushed (without this event) and a new transaction is started.

starts_when.source

The text of the condition. The syntax of the condition depends on the value of type.

starts_when.type

The type of condition to supply. See Available syntaxes below for a list of available types for this transform.

Available syntaxes

Syntax	Description	Example
`vrl`	A Vector Remap Language (VRL) Boolean expression.	`.status_code != 200 && !includes(["info", "debug"], .severity)`
`datadog_search`	A Datadog Search query string.	`*stack`
`is_log`	Whether the incoming event is a log.
`is_metric`	Whether the incoming event is a metric.
`is_trace`	Whether the incoming event is a trace.

Shorthand for VRL

Config format	Example
YAML	`condition: .status == 200`
TOML	`condition = ".status == 200"`
JSON	`"condition": ".status == 200"`

Condition config examples

Standard VRL

starts_when:
  type: "vrl"
  source: ".status == 500"

starts_when = { type = "vrl", source = ".status == 500" }

"starts_when": {
  "type": "vrl",
  "source": ".status == 500"
}

Datadog Search

starts_when:
  type: "datadog_search"
  source: "*stack"

starts_when = { type = "datadog_search", source = "*stack" }

"starts_when": {
  "type": "datadog_search",
  "source": "*stack"
}

VRL shorthand

starts_when: ".status == 500"

starts_when = ".status == 500"

"starts_when": ".status == 500"

Input Types

The following section shows which telemetry data types are supported.

Logs

Log events are supported.

Outputs

<component_id>

Default output stream of the component. Use this component’s ID as an input to downstream transforms and sinks.

Telemetry

Metrics

link

component_discarded_events_total

counter

The number of events dropped by this component.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

host optional

The hostname of the system Vector is running on.

intentional

True if the events were discarded intentionally, like a filter transform, or false if due to an error.

pid optional

The process ID of the Vector instance.

component_errors_total

counter

The total number of errors encountered by this component.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

error_type

The type of the error

host optional

The hostname of the system Vector is running on.

pid optional

The process ID of the Vector instance.

stage

The stage within the component at which the error occurred.

component_received_event_bytes_total

counter

The number of event bytes accepted by this component either from tagged origins like file and uri, or cumulatively from other origins.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

container_name optional

The name of the container from which the data originated.

file optional

The file from which the data originated.

host optional

The hostname of the system Vector is running on.

mode optional

The connection mode used by the component.

peer_addr optional

The IP from which the data originated.

peer_path optional

The pathname from which the data originated.

pid optional

The process ID of the Vector instance.

pod_name optional

The name of the pod from which the data originated.

uri optional

The sanitized URI from which the data originated.

component_received_events_count

histogram

A histogram of the number of events passed in each internal batch in Vector’s internal topology.

Note that this is separate than sink-level batching. It is mostly useful for low level debugging performance issues in Vector due to small internal batches.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

container_name optional

The name of the container from which the data originated.

file optional

The file from which the data originated.

host optional

The hostname of the system Vector is running on.

mode optional

The connection mode used by the component.

peer_addr optional

The IP from which the data originated.

peer_path optional

The pathname from which the data originated.

pid optional

The process ID of the Vector instance.

pod_name optional

The name of the pod from which the data originated.

uri optional

The sanitized URI from which the data originated.

component_received_events_total

counter

The number of events accepted by this component either from tagged origins like file and uri, or cumulatively from other origins.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

container_name optional

The name of the container from which the data originated.

file optional

The file from which the data originated.

host optional

The hostname of the system Vector is running on.

mode optional

The connection mode used by the component.

peer_addr optional

The IP from which the data originated.

peer_path optional

The pathname from which the data originated.

pid optional

The process ID of the Vector instance.

pod_name optional

The name of the pod from which the data originated.

uri optional

The sanitized URI from which the data originated.

component_sent_event_bytes_total

counter

The total number of event bytes emitted by this component.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

host optional

The hostname of the system Vector is running on.

output optional

The specific output of the component.

pid optional

The process ID of the Vector instance.

component_sent_events_total

counter

The total number of events emitted by this component.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

host optional

The hostname of the system Vector is running on.

output optional

The specific output of the component.

pid optional

The process ID of the Vector instance.

stale_events_flushed_total

counter

The number of stale events that Vector has flushed.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

host optional

The hostname of the system Vector is running on.

pid optional

The process ID of the Vector instance.

utilization

gauge

A ratio from 0 to 1 of the load on a component. A value of 0 would indicate a completely idle component that is simply waiting for input. A value of 1 would indicate a that is never idle. This value is updated every 5 seconds.

component_id

The Vector component ID.

component_kind

The Vector component kind.

component_type

The Vector component type.

host optional

The hostname of the system Vector is running on.

pid optional

The process ID of the Vector instance.

Examples

Merge Ruby exceptions

Given this event...

[{"log":{"host":"host-1.hostname.com","message":"foobar.rb:6:in `/': divided by 0 (ZeroDivisionError)","pid":1234,"tid":5678,"timestamp":"2020-10-07T12:33:21.223543Z"}},{"log":{"host":"host-1.hostname.com","message":"    from foobar.rb:6:in `bar'","pid":1234,"tid":5678,"timestamp":"2020-10-07T12:33:21.223543Z"}},{"log":{"host":"host-1.hostname.com","message":"    from foobar.rb:2:in `foo'","pid":1234,"tid":5678,"timestamp":"2020-10-07T12:33:21.223543Z"}},{"log":{"host":"host-1.hostname.com","message":"    from foobar.rb:9:in `\u003cmain\u003e'","pid":1234,"tid":5678,"timestamp":"2020-10-07T12:33:21.223543Z"}},{"log":{"host":"host-1.hostname.com","message":"Hello world, I am a new log","pid":1234,"tid":5678,"timestamp":"2020-10-07T12:33:22.123528Z"}}]

...and this configuration...

transforms:
  my_transform_id:
    type: reduce
    inputs:
      - my-source-or-transform-id
    group_by:
      - host
      - pid
      - tid
    merge_strategies:
      message: concat_newline
      pid: discard
      tid: discard
    starts_when: match(string!(.message), r'^[^\s]')

[transforms.my_transform_id]
type = "reduce"
inputs = [ "my-source-or-transform-id" ]
group_by = [ "host", "pid", "tid" ]
starts_when = "match(string!(.message), r'^[^\\s]')"

  [transforms.my_transform_id.merge_strategies]
  message = "concat_newline"
  pid = "discard"
  tid = "discard"

{
  "transforms": {
    "my_transform_id": {
      "type": "reduce",
      "inputs": [
        "my-source-or-transform-id"
      ],
      "group_by": [
        "host",
        "pid",
        "tid"
      ],
      "merge_strategies": {
        "message": "concat_newline",
        "pid": "discard",
        "tid": "discard"
      },
      "starts_when": "match(string!(.message), r'^[^\\s]')"
    }
  }
}

...this Vector event is produced:

[{"log":{"host":"host-1.hostname.com","message":"foobar.rb:6:in `/': divided by 0 (ZeroDivisionError)\n    from foobar.rb:6:in `bar'\n    from foobar.rb:2:in `foo'\n    from foobar.rb:9:in `\u003cmain\u003e'","pid":1234,"tid":5678,"timestamp":"2020-10-07T12:33:21.223543Z"}},{"log":{"host":"host-1.hostname.com","message":"Hello world, I am a new log","pid":1234,"tid":5678,"timestamp":"2020-10-07T12:33:22.123528Z"}}]

Reduce Rails logs into a single transaction

Given this event...

[{"log":{"message":"Received GET /path","request_id":"abcd1234","request_params":{"key":"val"},"request_path":"/path","timestamp":"2020-10-07T12:33:21.223543Z"}},{"log":{"message":"Executed query in 5.2ms","query":"SELECT * FROM table","query_duration_ms":5.2,"request_id":"abcd1234","timestamp":"2020-10-07T12:33:21.832345Z"}},{"log":{"message":"Rendered partial _partial.erb in 2.3ms","render_duration_ms":2.3,"request_id":"abcd1234","template":"_partial.erb","timestamp":"2020-10-07T12:33:22.457423Z"}},{"log":{"message":"Executed query in 7.8ms","query":"SELECT * FROM table","query_duration_ms":7.8,"request_id":"abcd1234","timestamp":"2020-10-07T12:33:22.543323Z"}},{"log":{"message":"Sent 200 in 15.2ms","request_id":"abcd1234","response_duration_ms":5.2,"response_status":200,"timestamp":"2020-10-07T12:33:22.742322Z"}}]

...and this configuration...

transforms:
  my_transform_id:
    type: reduce
    inputs:
      - my-source-or-transform-id

[transforms.my_transform_id]
type = "reduce"
inputs = [ "my-source-or-transform-id" ]

{
  "transforms": {
    "my_transform_id": {
      "type": "reduce",
      "inputs": [
        "my-source-or-transform-id"
      ]
    }
  }
}

...this Vector event is produced:

{
  "message": "Received GET /path",
  "query": "SELECT * FROM table",
  "query_duration_ms": 13,
  "render_duration_ms": 2.3,
  "request_id": "abcd1234",
  "request_params": {
    "key": "val"
  },
  "request_path": "/path",
  "response_duration_ms": 5.2,
  "response_status": 200,
  "template": "_partial.erb",
  "timestamp": "2020-10-07T12:33:21.223543Z"
}

How it works

State

This component is stateful, meaning its behavior changes based on previous inputs (events). State is not preserved across restarts, therefore state-dependent behavior will reset between restarts and depend on the inputs (events) received since the most recent restart.