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tcp

The in_tcp Input plugin enables Fluentd to accept TCP payload.

It is included in Fluentd's core.

Don't use this plugin for receiving logs from Fluentd client libraries. Use in_forward for such cases.

Example Configuration

<source>
  @type tcp
  tag tcp.events # required
  <parse>
    @type regexp
    expression /^(?<field1>\d+):(?<field2>\w+)$/
  </parse>
  port 20001   # optional. 5170 by default
  bind 0.0.0.0 # optional. 0.0.0.0 by default
  delimiter "\n" # optional. "\n" (newline) by default
</source>

Example input:

$ echo '123456:awesome' | netcat 0.0.0.0 5170

Parsed result:

{"field1":"123456","field2":"awesome"}

Refer to the Configuration File article for the basic structure and syntax of the configuration file.

For <parse>, see Parse Section.

We have observed drastic performance improvements on Linux, with proper kernel parameter settings. If you have high-volume TCP traffic, follow Before Installing Fluentd instructions.

Plugin Helpers

Parameters

See Common Parameters.

@type

The value must be tcp.

tag

type default version
string required parameter 0.14.0

The tag of output events.

port

type default version
integer 5170 0.14.0

The port to listen to.

bind

type default version
string 0.0.0.0 (all addresses) 0.14.0

The bind address to listen to.

source_hostname_key

type default version
string nil (no adding hostname) 0.14.10

The field name of the client's hostname. If set, the client's hostname will be set to its key. The default is nil (no adding hostname).

With this configuration:

source_hostname_key client_host

The client's hostname is set to client_host field:

{
    ...
    "foo": "bar",
    "client_host": "client.hostname.org"
}

source_address_key

type default version
string nil (no adding source address) 1.4.2

The field name for the client's IP address. If set, Fluentd automatically adds the remote address to each data record.

For example, if you have the following configuration:

<source>
  @type tcp
  source_address_key client_addr
  # ...
</source>

You will get something like below:

{
    ...
    "client_addr": "192.168.10.10"
    ...
}

message_length_limit

type default version
size nil (no limit) 1.16.1

The maximum number of bytes for the message.

<transport> Section

type default available values version
enum tcp tcp, tls 0.14.12

This section is for setting TLS transport or some general transport configurations. See Config: Transport Section for all supported parameters.

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.

{% hint style='info' %} On Windows, Fluentd sends FIN without depending on this setting. {% endhint %}

<source>
  @type tcp
  # other plugin parameters
  <transport tcp>
    linger_timeout 1
  </transport>
</source>
send_keepalive_packet
type default available transport type version
bool false tcp, tls 1.16.0

Enable SO_KEEPALIVE on the underlying TCP sockets.

This is useful when you connect to Fluentd over firewalls or proxies and want to prevent connections from being closed automatically.

TLS configuration

<transport tls>
  cert_path /path/to/fluentd.crt
  # ...
</transport>

See How to Enable TLS Encryption section for how to use and see Configuration Example for all supported parameters.

Without <transport tls>, in_tcp uses raw TCP.

<security> Section

required multi version
false false 1.7.2

Adds <security>/<client> section to allow access by Host/IP/Network.

<client> Section

host

type default version
string nil 1.7.2

The IP address or host name of the client.

This is exclusive with network.

network

type default version
string nil 1.7.2

Network address specification.

This is exclusive with host.

<parse> Section

required multi version
true false 0.14.10

in_tcp uses the parser plugin to parse the payload.

For more details:

Code Example

Here is a Ruby example to send an event to in_tcp:

require 'socket'

# This example uses json payload.
# In in_tcp configuration, need to configure "@type json" in "<parse>"
TCPSocket.open('127.0.0.1', 5170) do |s|
  s.write('{"k":"v1"}' + "\n")
  s.write('{"k":"v2"}' + "\n")
end

Tips

How to Enable TLS Encryption

in_tcp supports TLS transport.

Example:

<source>
  @type tcp
  port 5140
  bind 0.0.0.0
  <transport tls>
    ca_path /etc/pki/ca.pem
    cert_path /etc/pki/cert.pem
    private_key_path /etc/pki/key.pem
    private_key_passphrase PASSPHRASE
  </transport>
  tag tcp
</source>

How to Enable TLS Mutual Authentication

Fluentd supports TLS mutual authentication (i.e. client certificate auth). If you want to use this feature, please set the client_cert_auth and ca_path options like this:

<source>
  @type tcp
  port 20001
  <transport tls>
    # ...
    client_cert_auth true
    ca_path /path/to/ca/cert
  </transport>
</source>

When this feature is enabled, Fluentd will check all the incoming requests for a client certificate signed by the trusted CA. Requests with an invalid client certificate will fail.

To check if mutual authentication is working properly, issue these commands:

$ openssl s_client -connect localhost:20001 \
  -key path/to/client.key \
  -cert path/to/client.crt \
  -CAfile path/to/ca.crt

If the connection gets established successfully, your setup is working fine.

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.