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Plugin Helper: Server
The server plugin helper manages various types of servers.
Here is an example:
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require 'fluent/plugin/input'
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module Fluent::Plugin
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class ExampleInput < Input
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Fluent::Plugin.register_input('example', self)
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# 1. Load server helper
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helpers :server
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# Omit `configure`, `shutdown` and other plugin APIs
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def start
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# 2. Create server
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server_create(:title, @port) do |data|
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#3. Process data
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end
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end
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end
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end
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The launched server is managed by the plugin helper. No need of server shutdown code in plugin's shutdown method. The plugin shutdowns the launched servers automatically.
For more details, see Transport Section.

Methods

server_create_connection(title, port, proto: nil, bind: '0.0.0.0', shared: true, backlog: nil, tls_options: nil, **socket_options, &block)

This method creates a server instance for various protocols.
The &block is invoked with the new connection as a parameter.
  • title: unique symbol
  • port: the port to listen to
  • proto: protocol type. { :tcp, :tls }
  • bind: the bind address to listen to
  • shared: if true, share socket via server engine for multiple workers
  • backlog: the maximum length of the queue for pending connections
  • tls_options: options for TLS
    • version: set TLS version :TLSv1_1 or :TLSv1_2.
      Default: :TLSv1_2
    • ciphers: set the list of available cipher suites. (default:
      "ALL:!aNULL:!eNULL:!SSLv2")
    • insecure: if true, set TLS verify mode NONE
    • cert_verifier: if specified, pass evaluated object to OpenSSL's verify_callback. See also "cert_verifier example" section.
    • verify_fqdn: if true, validate the server certificate for the hostname
    • fqdn: set FQDN
    • enable_system_cert_store: if true, enable system default cert store
    • allow_self_signed_cert: if true, allow self-signed certificate
    • cert_paths: files contain PEM-encoded certificates
  • socket_options: options for socket
    • resolve_name: if true, resolve the hostname
    • connect: if true, connect to host
    • nonblock: if true, use non-blocking I/O
    • linger_timeout: the timeout (seconds) to set SO_LINGER
    • recv_timeout: the timeout (seconds) to set SO_RECVTIMEO
    • send_timeout: the timeout (seconds) to set SO_SNDTIMEO
    • send_keepalive_packet: if true, enable TCP keep-alive via SO_KEEPALIVE. See also socket article.
Example:
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# TCP
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server_create_connection(:title, @port) do |conn|
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# on connection
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# conn is Fluent::PluginHelper::Server::TCPCallbackSocket
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source_addr = conn.remote_host
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source_port = conn.remote_port
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conn.data do |data|
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conn.write(something)
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end
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end
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server_create(title, port, proto: nil, bind: '0.0.0.0', shared: true, socket: nil, backlog: nil, tls_options: nil, max_bytes: nil, flags: 0, **socket_options, &callback)

This method creates a server instance for various protocols.
The &block is invoked with parameter(s) on data.
  • title: unique symbol
  • port: the port to listen to
  • proto: protocol type. { :tcp, :udp, :tls }
  • bind: the bind address to listen to
  • shared: if true, share socket via server engine for multiple workers
  • socket: socket instance for UDP (only for UDP)
  • backlog: the maximum length of the queue for pending connections
  • tls_options: options for TLS
    • version: set TLS version :TLSv1_1 or :TLSv1_2. (default: :TLSv1_2)
    • ciphers: set the list of available cipher suites. (default:
      "ALL:!aNULL:!eNULL:!SSLv2")
    • insecure: if true, set TLS verify mode NONE
    • cert_verifier: if specified, pass evaluated object to OpenSSL's verify_callback. See also "cert_verifier example" section.
    • verify_fqdn: if true, validate the server certificate for the hostname
    • fqdn: set FQDN
    • enable_system_cert_store: if true, enable system default cert store
    • allow_self_signed_cert: if true, allow self signed certificate
    • cert_paths: files contain PEM-encoded certificates
  • max_bytes: the maximum number of bytes to receive (required for UDP)
  • flags: zero or more of the MSG_ options (UDP-only)
  • socket_options: options for socket
    • resolve_name: if true, resolve the hostname
    • connect: if true, connect to host
    • nonblock: if true, use non-blocking I/O
    • linger_timeout: the timeout (seconds) to set SO_LINGER
    • recv_timeout: the timeout (seconds) to set SO_RECVTIMEO
    • send_timeout: the timeout (seconds) to set SO_SNDTIMEO
    • send_keepalive_packet: if true, enable TCP keep-alive via SO_KEEPALIVE. See also socket article.
Code example:
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# UDP (w/o socket)
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server_create(:title, @port, proto: :udp, max_bytes: 2048) do |data|
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# data is received data
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end
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# UDP (w/ socket)
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server_create(:title, @port, proto: :udp, max_bytes: 2048) do |data, sock|
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# data is received data
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# sock is UDPSocket
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end
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# TCP (w/o connection)
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server_create(:title, @port) do |data|
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# data is received data
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end
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# TCP (w/ connection)
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server_create(:title, @port) do |data, conn|
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# data is received data
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# conn is Fluent::PluginHelper::Server::TCPCallbackSocket
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end
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# TLS (w/o connection)
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server_create(:title, @port, proto: :tls) do |data|
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# data is received data
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end
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# TLS (w/ connection)
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server_create(:title, @port, proto: :tls) do |data, conn|
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# data is received data
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# conn is Fluent::PluginHelper::Server::TLSCallbackSocket
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end
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Configuration example

General configuration

linger_timeout

type
default
available transport type
version
integer
0
tcp, tls
1.14.6
The timeout (seconds) to set SO_LINGER.
The default value 0 is to send RST rather than FIN to avoid lots of connections sitting in TIME_WAIT on closing on non-Windows.
You can set positive value to send FIN on closing on non-Windows.
(On Windows, Fluentd sends FIN when linger_timeout is 0 too).
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<source>
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@type tcp
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# other plugin parameters
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<transport tcp>
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linger_timeout 1
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</transport>
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</source>
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TLS configuration: Basic examples

  1. 1.
    Use existing certs (signed by public CA or self signed CA)
  2. 2.
    Use certs automatically generated by Fluentd
Case 1. Use existing certs (signed by public CA or self signed CA)
If cert_path and private_key_path are specified, certs generation is disabled. The existing certs are loaded.
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<source>
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@type forward
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# other plugin parameters
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<transport tls>
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version TLSv1_2
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ciphers ALL:!aNULL:!eNULL:!SSLv2
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insecure false
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# For Cert signed by public CA
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ca_path /path/to/ca_file
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cert_path /path/to/cert_path
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private_key_path /path/to/priv_key
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private_key_passphrase "passphrase"
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client_cert_auth false
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# For Cert signed by self signed CA
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ca_path /path/to/ca_path
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cert_path /path/to/cert_path
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private_key_path /path/to/priv_key
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private_key_passphrase "passphrase"
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client_cert_auth false
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</transport>
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</source>
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Case 2. Use certs automatically generated by Fluentd
If ca_cert_path and ca_private_key_path are specified, certs generation is enabled. You can customize cert generation behavior via generation_... parameters. See Generated and Signed by Private CA Certs or Self-signed Parameters about parameter details.
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<source>
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@type forward
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# other plugin parameters
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<transport tls>
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version TLSv1_2
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ciphers ALL:!aNULL:!eNULL:!SSLv2
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insecure false
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# For Cert generated
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ca_cert_path /path/to/ca_cert
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ca_private_key_path /path/to/ca_priv_key
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ca_private_key_passphrase "ca_passphrase"
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</transport>
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</source>
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TLS configuration: cert_verifier example

cert_verifier is supported since v1.10.0.
Configuration example:
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<source>
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@type forward
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<transport tls>
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# other parameters
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client_cert_auth true
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cert_verifier /path/to/my_verifier.rb
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</transport>
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</source>
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  • my_verifier.rb example
The code must return a callable object that has a call method with two arguments. This object is used as OpenSSL's verify_callback.

Proc or lambda Object for the Simple Scenario

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Proc.new { |ok, ctx|
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# check code
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if cond
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true
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else
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false
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end
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}
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Use class for the Complicated Scenario

This is CN check example:
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module Fluent
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module Plugin
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class InForwardCNChecker
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def initialize
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# Modify for actual common names
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@allow_list = ['fluentd', 'fluentd-client', 'other-org']
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end
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def call(ok, ctx)
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subject = ctx.chain.first.subject.to_a.find { |entry| entry.first == 'CN' }
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if subject
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@allow_list.include?(subject[1])
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else
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false
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end
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end
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end
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end
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end
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Fluent::Plugin::InForwardCNChecker.new
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Plugins using server

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.