Configuration Parameter Types

Types of Configuration Parameters

Common Options

• default: Specifies the default value for a parameter. If omitted, the

  parameter is required. On startup, Fluentd uses the default value instead if

  the parameter is not configured.

  NOTE: It doesn't perform type conversion such as time type, and the specified default value is used as is.

# Required parameter: The configuration must have this parameter like 'param1 10'.
config_param :param1, :integer

# Optional parameter: If the configuration doesn't have 'param2', 100 is used.
config_param :param2, :integer, default: 100

• secret: If true, the parameter will be masked when Fluentd dumps its

  configuration on the standard output on startup.

config_param :secret_param, :string, secret: true

• deprecated: Specifies the deprecation warning message. If users use this

  parameter in the configuration, they will see the deprecation warning on

  startup.

config_param :old_param, :string, deprecated: "Use new_param instead"

• obsoleted: Specifies the obsolete error message. If users use this parameter

  in the configuration, Fluentd raises Fluent::ConfigError and stops.

config_param :dead_param, :string, obsoleted: "This parameter doesn't work anymore"

• alias: Alias for this parameter as a symbol.

• skip_accessor: If true, skip adding accessor to the plugin. For internal

  use only!

Data Types

:string

Defines a string parameter.

Code Example:

config_param :name, :string, default: "John Doe", alias: :full_name
config_param :password, :string, secret: true

def configure(conf)
  super

  log.info(name: @name, password: @password)
end

Configuration Example:

name John Titor
password very-secret-password

:regexp

Defines a regexp parameter. Since v1.2.0.

Code Example:

config_param :pattern, :regexp, default: /^key_/

def configure(conf)
  super

  log.info(pattern: @pattern)
end

def filter(tag, time, record)
  new_record = record.select do |k, v|
    @pattern.match(k)
  end
  new_record
end

Configuration Example:

pattern /^name_/
pattern ^name_    # Also support pattern without slashes

:integer

Defines an integer parameter.

Code Example:

config_param :num_children, :integer, default: 1

def start
  super
  # ...
  @num_children.times do |n|
    # do something...
  end
end

Configuration Example:

num_children 10

:float

Defines a float parameter.

Code Example:

helpers :timer
config_param :interval, :float, default: 0.5

def start
  super
  # ...
  timer_execute(:in_example, @interval) do
    # do something periodically
  end
end

Configuration Example:

interval 1.5

:size

Defines a size parameter in bytes.

Available suffixes: { k, m, g, t } (ignore case)

Code Example:

config_param :limit, :size

def do_something
  raise "overflow!" if @limit < current
  # ...
end

Configuration Example:

limit 10  # 10 byte
limit 10k # 10240 byte
limit 10m # 10485760 byte
limit 10g # 10737418240 byte
limit 10t # 10995116277760 byte

Configuration Example:

limit 10m

:time

Defines the length of the time parameter.

Available suffixes: { s, m, h, d } (lower case only).

If omitted, to_f is applied to the value which converts it to seconds.

Code Example:

config_param :interval, :time

def start
  timer_execute(:in_example, @interval) do
    # do something periodically
  end
end

Configuration Example:

interval 0.5 # 0.5 seconds
interval 1s  # 1 second
interval 1m  # 1 minute = 60 seconds
interval 1h  # 1 hour = 3600 seconds
interval 1d  # 1 day = 86400 seconds

Configuration Example:

interval 10m

:bool

Defines a Boolean parameter.

Code Example:

config_param :deep_copy, :bool, default: false

def copy(object)
  if @deep_copy
    # deep copy
  else
    # shallow copy
  end
end

Configuration Example:

deep_copy true

:enum

Defines an enumerated parameter.

Users can choose a value from the list. If a non-listed value is chosen, an error occurs on startup.

• Available options

  • list: List of available values.

Code Example:

config_param :protocol_type, :enum, list: [:udp, :tcp], default: :udp

def send
  case @protocol_type
  when :udp
    send_udp
  when :tcp
    send_tcp
  end
end

Configuration Example:

protocol_type tcp

:array

Defines an array parameter.

Users can set an array value for a parameter.

• Available options

  • value_type: Defines the type of the value.

    Available types: { :string, :integer, :float, :size, :bool, :time }

Code Example:

config_param :users, :array, default: [], value_type: :string

def available_user?(user)
  @users.include?(user)
end

Configuration Example:

users user1, user2, user3
users ["user1", "user2", "user3"] # written in JSON

This configuration will be converted to:

["user1", "user2", "user3"]

:hash

Defines a hash parameter.

• Available options

  • symbolize_keys: If true, the keys are symbolized.

  • value_type: Defines the same type for all values.

Code Example:

config_param :key_values, :hash, default: {}, symbolize_keys: true, value_type: :string

def do_something
  value1 = @key_values[:key1]
  value2 = @key_values[:key2]
  # ...
end

Configuration Example:

key_values {"key1": "value1", "key2": "value2"} # written in JSON
key_values key1:value1,key2:value2

This configurations will be converted to:

{ key1: "value1", key2: "value2" }

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.