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tls: Add descriptions for x509v3 alt name verification (tls.verify_hostname) #1393

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Jun 27, 2024
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tls: Add descriptions for x509v3 alt name verification (tls.verify_hostname) #1393

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tls: Add a description for tls.verify_hostname parameter
cosmo0920 Jun 17, 2024
6c3f5d0
filter_kubernetes: Add a description for tls.verify_hostname
cosmo0920 Jun 17, 2024
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cosmo0920 Jun 21, 2024
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40 changes: 40 additions & 0 deletions administration/transport-security.md
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ Both input and output plugins that perform Network I/O can optionally enable TLS
| :--- | :--- | :--- |
| tls | enable or disable TLS support | Off |
| tls.verify | force certificate validation | On |
| tls.verify\_hostname | force TLS verification of hostnames | Off |
| tls.debug | Set TLS debug verbosity level. It accept the following values: 0 \(No debug\), 1 \(Error\), 2 \(State change\), 3 \(Informational\) and 4 Verbose | 1 |
| tls.ca\_file | absolute path to CA certificate file | |
| tls.ca\_path | absolute path to scan for certificate files | |
Expand Down Expand Up @@ -171,3 +172,42 @@ Fluent Bit supports [TLS server name indication](https://en.wikipedia.org/wiki/S
tls.ca_file /etc/certs/fluent.crt
tls.vhost fluent.example.com
```

### Verify subjectAltName

By default, TLS verification of hostnames is not done automatically.
As an example, we can extract the X509v3 Subject Alternative Name from a certificate:

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

As you can see, this certificate covers only `my.fluent-aggregator.net` so if we use a different hostname it should fail.

To fully verify the alternative name and demonstrate the failure we enable `tls.verify_hostname`:


```text
[INPUT]
Name cpu
Tag cpu

[OUTPUT]
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 be failed and disconnected:

```
[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
```
1 change: 1 addition & 0 deletions pipeline/filters/kubernetes.md
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Expand Up @@ -37,6 +37,7 @@ The plugin supports the following configuration parameters:
| Keep\_Log | When `Keep_Log` is disabled, the `log` field is removed from the incoming message once it has been successfully merged \(`Merge_Log` must be enabled as well\). | On |
| tls.debug | Debug level between 0 \(nothing\) and 4 \(every detail\). | -1 |
| tls.verify | When enabled, turns on certificate validation when connecting to the Kubernetes API server. | On |
| tls.verify\_hostname | When enabled, turns on hostname validation for certificates | Off |
| Use\_Journal | When enabled, the filter reads logs coming in Journald format. | Off |
| Cache\_Use\_Docker\_Id | When enabled, metadata will be fetched from K8s when docker\_id is changed. | Off |
| Regex\_Parser | Set an alternative Parser to process record Tag and extract pod\_name, namespace\_name, container\_name and docker\_id. The parser must be registered in a [parsers file](https://github.com/fluent/fluent-bit/blob/master/conf/parsers.conf) \(refer to parser _filter-kube-test_ as an example\). | |
Expand Down