> For the complete documentation index, see [llms.txt](https://docs.fluentbit.io/manual/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fluentbit.io/manual/data-pipeline/outputs/udp.md).

# UDP

The *UDP* output plugin lets you send records to a remote UDP server. The payload can be formatted in different ways as required.

## Configuration parameters

This plugin supports the following parameters:

| Key                | Description                                                                                                                                  | Default      |
| ------------------ | -------------------------------------------------------------------------------------------------------------------------------------------- | ------------ |
| `format`           | Specify the data format to be printed. Supported formats: `msgpack`, `json`, `json_lines`, `json_stream`.                                    | `json_lines` |
| `host`             | Target host where the UDP server is listening.                                                                                               | `127.0.0.1`  |
| `json_date_format` | Specify the format of the date. Supported formats: `double`, `epoch`, `epoch_ms`, `iso8601`, `java_sql_timestamp`.                           | `double`     |
| `json_date_key`    | Specify the name of the time key in the output record. To disable the time key, set the value to `false`.                                    | `date`       |
| `port`             | UDP port of the target service.                                                                                                              | `5170`       |
| `raw_message_key`  | Use a raw message key for the message. When set, the plugin sends the value of this key as the raw message instead of formatting it as JSON. | *none*       |
| `workers`          | The number of [workers](/manual/administration/multithreading.md#outputs) to perform flush operations for this output.                       | `2`          |

## Get started

To send records to a `UDP` server, you can run the plugin from the command line or through the configuration file.

### Command line

The `UDP` plugin can read the parameters from the command line through the `-p` argument (property) or by setting them directly through the service URI. The URI format is the following:

```
udp://host:port
```

Using the format specified, start Fluent Bit through:

```shell
fluent-bit -i cpu -t cpu -o udp://192.168.2.3:5170 -p format=json_lines -v
```

which is similar to:

```shell
fluent-bit -i cpu -t cpu -o udp -p host=192.168.2.3 -p port=5170 \
  -p format=json_lines -o stdout -m '*'
```

### Configuration file

In your main configuration file append the following:

{% tabs %}
{% tab title="fluent-bit.yaml" %}

```yaml
pipeline:
  inputs:
    - name: cpu
      tag: cpu

  outputs:
    - name: udp
      match: '*'
      host: 192.168.2.3
      port: 5170
      format: json_lines
```

{% endtab %}

{% tab title="fluent-bit.conf" %}

```
[INPUT]
  Name cpu
  Tag  cpu

[OUTPUT]
  Name  udp
  Match *
  Host  192.168.2.3
  Port  5170
  Format json_lines
```

{% endtab %}
{% endtabs %}

## JSON format examples

### JSON lines format

This example sends CPU metrics in JSON lines format to a `UDP` server:

{% tabs %}
{% tab title="fluent-bit.yaml" %}

```yaml
pipeline:
  inputs:
    - name: cpu
      tag: cpu

  outputs:
    - name: udp
      match: '*'
      host: 127.0.0.1
      port: 5170
      format: json_lines
      json_date_key: timestamp
      json_date_format: iso8601
```

{% endtab %}

{% tab title="fluent-bit.conf" %}

```
[INPUT]
  Name cpu
  Tag  cpu

[OUTPUT]
  Name            udp
  Match           *
  Host            127.0.0.1
  Port            5170
  Format          json_lines
  Json_Date_Key   timestamp
  Json_Date_Format iso8601
```

{% endtab %}
{% endtabs %}

Run the following in a separate terminal, `netcat` will start listening for messages on `UDP` port `5170`:

```shell
nc -u -l 5170
```

After Fluent Bit connects, you should see output in JSON format:

```
{"timestamp":"2024-01-15T10:30:45.123456Z","cpu_p":1.1875,"user_p":0.5625,"system_p":0.625}
{"timestamp":"2024-01-15T10:30:46.123456Z","cpu_p":2.25,"user_p":2.0,"system_p":0.25}
```

### Raw message format

When `raw_message_key` is set, the plugin sends the value of the specified key as a raw message instead of applying formatting, causing the `format` property to be ignored:

{% tabs %}
{% tab title="fluent-bit.yaml" %}

```yaml
pipeline:
  inputs:
    - name: tail
      path: /var/log/app.log
      tag: app

  outputs:
    - name: udp
      match: '*'
      host: 127.0.0.1
      port: 5170
      raw_message_key: $message
```

{% endtab %}

{% tab title="fluent-bit.conf" %}

```
[INPUT]
  Name tail
  Path /var/log/app.log
  Tag  app

[OUTPUT]
  Name           udp
  Match          *
  Host           127.0.0.1
  Port           5170
  Raw_Message_Key $message
```

{% endtab %}
{% endtabs %}

The `$` sign is required to signal the record accessor to extract the value from the specified key - this can be a top-level or nested field:

{% tabs %}
{% tab title="Top-level field" %}
Example log:

```json
{
  "timestamp": "2026-07-05T14:32:07Z",
  "message": "<34>Jul  5 14:32:07 myhost kernel: Payload detected: 54 42 50 20 77 61 73 20 68 65 72 65"
}
```

Setting `raw_message_key` to `$message` will yield:

```
<34>Jul  5 14:32:07 myhost kernel: Payload detected: 54 42 50 20 77 61 73 20 68 65 72 65
```

{% endtab %}

{% tab title="Nested field" %}
Example log:

```json
{
  "timestamp": "2026-07-05T14:32:07Z",
  "message": {
    "original": "<34>Jul  5 14:32:07 myhost kernel: Payload detected: 54 42 50 20 77 61 73 20 68 65 72 65"
  }
}
```

Setting `raw_message_key` to `$message['original']` will yield:

```
<34>Jul  5 14:32:07 myhost kernel: Payload detected: 54 42 50 20 77 61 73 20 68 65 72 65
```

{% endtab %}
{% endtabs %}

## Message size limitations

`UDP` has a maximum datagram size of `65535` bytes. If a record exceeds this size, the plugin will send it but log a debug message. For large messages, consider using `TCP` or `HTTP` output plugins instead.

## Testing

To test the `UDP` output plugin, you can use `netcat` to listen for incoming `UDP` messages:

```shell
nc -u -l 5170
```

Or use `socat` for more advanced testing:

```shell
socat UDP-RECV:5170 STDOUT
```


---

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