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Transport Security

Fluent Bit provides integrated support for Transport Layer Security (TLS) and its predecessor Secure Sockets Layer (SSL). This section refers only to TLS for both implementations.

Both input and output plugins that perform Network I/O can optionally enable TLS and configure the behavior. The following table describes the properties available:

Property
Description
Default

tls

Enable or disable TLS support.

Off

tls.verify

Force certificate validation.

On

tls.verify_hostname

Force TLS verification of host names.

Off

tls.debug

Set TLS debug verbosity level. Accepted values: 0 (No debug), 1 (Error), 2 (State change), 3 (Informational) and 4. (Verbose)

1

tls.ca_file

Absolute path to CA certificate file.

none

tls.ca_path

Absolute path to scan for certificate files.

none

tls.crt_file

Absolute path to Certificate file.

none

tls.key_file

Absolute path to private Key file.

none

tls.key_passwd

Optional password for tls.key_file file.

none

tls.vhost

Hostname to be used for TLS SNI extension.

none

To use TLS on input plugins, you must provide both a certificate and a private key.

The listed properties can be enabled in the configuration file, specifically in each output plugin section or directly through the command line.

The following output plugins can take advantage of the TLS feature:

The following input plugins can take advantage of the TLS feature:

In addition, other plugins implement a subset of TLS support, with restricted configuration:

Example: enable TLS on HTTP input

By default, the HTTP input plugin uses plain TCP. Run the following command to enable TLS:

./bin/fluent-bit -i http \
           -p port=9999 \
           -p tls=on \
           -p tls.verify=off \
           -p tls.crt_file=self_signed.crt \
           -p tls.key_file=self_signed.key \
           -o stdout \
           -m '*'

See Tips & Trick section below for details on generating self_signed.crt and self_signed.key files shown in these examples.

In the previous command, the two properties tls and tls.verify are set for demonstration purposes. Always enable verification in production environments.

The same behavior can be accomplished using a configuration file:

pipeline:
    inputs:
      - name: http
        port: 9999
        tls: on
        tls.verify: off
        tls.cert_file: self_signed.crt
        tls.key_file: self_signed.key

    outputs:
      - name: stdout
        match: '*'

Example: enable TLS on HTTP output

By default, the HTTP output plugin uses plain TCP. Run the following command to enable TLS:

fluent-bit -i cpu -t cpu -o http://192.168.2.3:80/something \
    -p tls=on         \
    -p tls.verify=off \
    -m '*'

In the previous command, the properties tls and tls.verify are enabled for demonstration purposes. Always enable verification in production environments.

The same behavior can be accomplished using a configuration file:

pipeline:
    inputs:
      - name: cpu
        tag: cpu

    outputs:
      - name: http
        match: '*'
        host: 192.168.2.3
        port: 80
        uri: /something
        tls: on
        tls.verify: off

Tips and Tricks

Generate a self signed certificates for testing purposes

The following command generates a 4096 bit RSA key pair and a certificate that's signed using SHA-256 with the expiration date set to 30 days in the future. In this example,test.host.net is set as the common name. This example opts out of DES, so the private key is stored in plain text.

openssl req -x509 \
            -newkey rsa:4096 \
            -sha256 \
            -nodes \
            -keyout self_signed.key \
            -out self_signed.crt \
            -subj "/CN=test.host.net"

Connect to virtual servers using TLS

Fluent Bit supportsTLS server name indication. If you are serving multiple host names on a single IP address (for example, using virtual hosting), you can make use of tls.vhost to connect to a specific hostname.

pipeline:
    inputs:
      - name: cpu
        tag: cpu

    outputs:
      - name: forward
        match: '*'
        host: 192.168.10.100
        port: 24224
        tls: on
        tls.verify: off
        tls.ca_file: '/etc/certs/fluent.crt'
        tls.vhost: 'fluent.example.com'

Verify subjectAltName

By default, TLS verification of host names isn't done automatically. As an example, you can extract the X509v3 Subject Alternative Name from a certificate:

X509v3 Subject Alternative Name:
    DNS:my.fluent-aggregator.net

This certificate covers only my.fluent-aggregator.net so if you use a different hostname it should fail.

To fully verify the alternative name and demonstrate the failure, enabletls.verify_hostname:

pipeline:
    inputs:
      - name: cpu
        tag: cpu

    outputs:
      - name: forward
        match: '*'
        host: other.fluent-aggregator.net
        port: 24224
        tls: on
        tls.verify: on
        tls.verify_hostname: on
        tls.ca_file: '/path/to/fluent-x509v3-alt-name.crt'

This outgoing connect will fail and disconnect:

[2024/06/17 16:51:31] [error] [tls] error: unexpected EOF with reason: certificate verify failed
[2024/06/17 16:51:31] [debug] [upstream] connection #50 failed to other.fluent-aggregator.net:24224
[2024/06/17 16:51:31] [error] [output:forward:forward.0] no upstream connections available

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