Environment variables

The env section of YAML configuration files lets you define environment variables. These variables can then be used to dynamically replace values throughout your configuration using the ${VARIABLE_NAME} syntax.

Values set in the env section are case-sensitive. However, as a best practice, Fluent Bit recommends using uppercase names for environment variables. The following example defines two variables, FLUSH_INTERVAL and STDOUT_FMT, which can be accessed in the configuration using ${FLUSH_INTERVAL} and ${STDOUT_FMT}:

env:
  FLUSH_INTERVAL: 1
  STDOUT_FMT: 'json_lines'

service:
  flush: ${FLUSH_INTERVAL}
  log_level: info

pipeline:
  inputs:
    - name: random

  outputs:
    - name: stdout
      match: '*'
      format: ${STDOUT_FMT}

Predefined variables

Fluent Bit supports the following predefined environment variables. You can reference these variables in configuration files without defining them in the env section.

Name	Description
${HOSTNAME}	The system's hostname.

External variables

In addition to variables defined in the configuration file or the predefined ones, Fluent Bit can access system environment variables set in the user space. These external variables can be referenced in the configuration using the same ${VARIABLE_NAME} pattern.

Variables set in the env section can't be overridden by system environment variables.

For example, to set the FLUSH_INTERVAL system environment variable to 2 and use it in your configuration:

export FLUSH_INTERVAL=2

In the configuration file, you can then access this value as follows:

service:
  flush: ${FLUSH_INTERVAL}
  log_level: info

pipeline:
  inputs:
    - name: random

  outputs:
    - name: stdout
      match: '*'
      format: json_lines

This approach lets you manage and override configuration values using environment variables, providing flexibility in various deployment environments.