Standard Input

The stdin plugin supports retrieving a message stream from the standard input interface (stdin) of the Fluent Bit process. In order to use it, specify the plugin name as the input, e.g:

$ fluent-bit -i stdin -o stdout

If the stdin stream is closed (end-of-file), the stdin plugin will instruct Fluent Bit to exit with success (0) after flushing any pending output.

Input formats

If no parser is configured for the stdin plugin, it expects valid JSON input data in one of the following formats:

1. A JSON object with one or more key-value pairs: { "key": "value", "key2": "value2" }

2. A 2-element JSON array in Fluent Bit Event format, which may be:

• [TIMESTAMP, { "key": "value" }] where TIMESTAMP is a floating point value representing a timestamp in seconds; or

• from Fluent Bit v2.1.0, [[TIMESTAMP, METADATA], { "key": "value" }] where TIMESTAMP has the same meaning as above and and METADATA is a JSON object.

Multi-line input JSON is supported.

Any input data that is not in one of the above formats will cause the plugin to log errors like:

[debug] [input:stdin:stdin.0] invalid JSON message, skipping
[error] [input:stdin:stdin.0] invalid record found, it's not a JSON map or array

To handle inputs in other formats, a parser must be explicitly specified in the configuration for the stdin plugin. See parser input example for sample configuration.

Log event timestamps

The Fluent Bit event timestamp will be set from the input record if the 2-element event input is used or a custom parser configuration supplies a timestamp. Otherwise the event timestamp will be set to the timestamp at which the record is read by the stdin plugin.

Examples

Json input example

A better example to demonstrate how it works will be through a Bash script that generates messages and writes them to Fluent Bit. Write the following content in a file named test.sh:

#!/bin/sh

for ((i=0; i<=5; i++)); do
  echo -n "{\"key\": \"some value\"}"
  sleep 1
done

Now lets start the script and Fluent Bit:

$ bash test.sh | fluent-bit -q -i stdin -o stdout
[0] stdin.0: [[1684196745.942883835, {}], {"key"=>"some value"}]
[0] stdin.0: [[1684196746.938949056, {}], {"key"=>"some value"}]
[0] stdin.0: [[1684196747.940162493, {}], {"key"=>"some value"}]
[0] stdin.0: [[1684196748.941392297, {}], {"key"=>"some value"}]
[0] stdin.0: [[1684196749.942644238, {}], {"key"=>"some value"}]
[0] stdin.0: [[1684196750.943721442, {}], {"key"=>"some value"}]

Json input with timestamp example

An input event timestamp may also be supplied. Replace test.sh with:

#!/bin/sh

for ((i=0; i<=5; i++)); do
  echo -n "
    [
      $(date '+%s.%N' -d '1 day ago'),
      {
        \"realtimestamp\": $(date '+%s.%N')
      }
    ]
  "
  sleep 1
done

Re-run the sample command. Note that the timestamps output by Fluent Bit are now one day old because Fluent Bit used the input message timestamp.

$ bash test.sh | fluent-bit -q -i stdin -o stdout
[0] stdin.0: [[1684110480.028171300, {}], {"realtimestamp"=>1684196880.030070}]
[0] stdin.0: [[1684110481.033753395, {}], {"realtimestamp"=>1684196881.034741}]
[0] stdin.0: [[1684110482.036730051, {}], {"realtimestamp"=>1684196882.037704}]
[0] stdin.0: [[1684110483.039903879, {}], {"realtimestamp"=>1684196883.041081}]
[0] stdin.0: [[1684110484.044719457, {}], {"realtimestamp"=>1684196884.046404}]
[0] stdin.0: [[1684110485.048710107, {}], {"realtimestamp"=>1684196885.049651}]

Json input with metadata example

Additional metadata is also supported on Fluent Bit v2.1.0 and above by replacing the timestamp with a 2-element object, e.g.:

#!/bin/sh
for ((i=0; i<=5; i++)); do
  echo -n "
    [
      [
        $(date '+%s.%N' -d '1 day ago'),
	{\"metakey\": \"metavalue\"}
      ],
      {
        \"realtimestamp\": $(date '+%s.%N')
      }
    ]
  "
  sleep 1
done

$ bash ./test.sh | fluent-bit -q -i stdin -o stdout
[0] stdin.0: [[1684110513.060139417, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196913.061017}]
[0] stdin.0: [[1684110514.063085317, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196914.064145}]
[0] stdin.0: [[1684110515.066210508, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196915.067155}]
[0] stdin.0: [[1684110516.069149971, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196916.070132}]
[0] stdin.0: [[1684110517.072484016, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196917.073636}]
[0] stdin.0: [[1684110518.075428724, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196918.076292}]

On older Fluent Bit versions records in this format will be discarded. Fluent Bit will log:

[ warn] unknown time format 6

if the log level permits.

Parser input example

To capture inputs in other formats, specify a parser configuration for the stdin plugin.

For example, if you want to read raw messages line-by-line and forward them you could use a parser.conf that captures the whole message line:

[PARSER]
    name        stringify_message
    format      regex
    Key_Name    message
    regex       ^(?<message>.*)

then use that in the parser clause of the stdin plugin in the fluent-bit.conf:

[INPUT]
    Name    stdin
    Tag     stdin
    Parser  stringify_message

[OUTPUT]
    Name   stdout
    Match  *

Fluent Bit will now read each line and emit a single message for each input line:

$ seq 1 5 | /opt/fluent-bit/bin/fluent-bit -c fluent-bit.conf -R parser.conf -q
[0] stdin: [1681358780.517029169, {"message"=>"1"}]
[1] stdin: [1681358780.517068334, {"message"=>"2"}]
[2] stdin: [1681358780.517072116, {"message"=>"3"}]
[3] stdin: [1681358780.517074758, {"message"=>"4"}]
[4] stdin: [1681358780.517077392, {"message"=>"5"}]
$

In real-world deployments it is best to use a more realistic parser that splits messages into real fields and adds appropriate tags.

Configuration Parameters

The plugin supports the following configuration parameters:

Key	Description	Default
Buffer_Size	Set the buffer size to read data. This value is used to increase buffer size. The value must be according to the Unit Size specification.	16k
Parser	The name of the parser to invoke instead of the default JSON input parser