feat: add information about fluentd tls connection

[enoot]

Description

I added information about TLS support for Fluentd log driver connection
https://github.com/moby/moby/blob/294f0c36e468dc097d56dcf88d4418b7dc3d2856/vendor/github.com/fluent/fluent-logger-golang/fluent/fluent.go#L443

Related issues or tickets

• relates to vendor: github.com/fluent/fluent-logger-golang v1.8.0 moby/moby#42979
• relates to TLS Support fluent/fluent-logger-golang#107
• relates to Add a new option TLSCertPath fluent/fluent-logger-golang#112

Reviews

• Technical review
• Editorial review
• Product review

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[thaJeztah]

Thanks! Looks indeed that the updated dependency from moby/moby#42979 add this as option (as part of docker engine v23.0 and up).

Looking a bit further, I see that a colleague (@akerouanton) left a comment in the PR that implemented it in the dependency; mentioning that it was "incomplete"; fluent/fluent-logger-golang#107 (comment)

Although this PR allows using self-signed TLS certs, it doesn't offer proper way of securely doing TLS because there's no way to specify which CA cert is accepted. With this change, if an attacker can mitm/redirect fluentd's network stream, they could still generate their own self-signed cert and bypass TLS promises. IMHO it could give a false sense of security. It would be great to be able to specify which CA certs are accepted (on top of what's in system truststore).

• ☝️ tracking ticket for that is in Add a new option TLSCertPath fluent/fluent-logger-golang#112

So, wondering if it was intentionally left undocumented (because of that), or if it's something we should (somewhere?) call out in the docs, in case users try to use the option and run into issues because of that limitation.

cc @akerouanton @vvoland for thoughts

[enoot]

Thanks! Looks indeed that the updated dependency from moby/moby#42979 add this as option (as part of docker engine v23.0 and up).

Looking a bit further, I see that a colleague (@akerouanton) left a comment in the PR that implemented it in the dependency; mentioning that it was "incomplete"; fluent/fluent-logger-golang#107 (comment)

Although this PR allows using self-signed TLS certs, it doesn't offer proper way of securely doing TLS because there's no way to specify which CA cert is accepted. With this change, if an attacker can mitm/redirect fluentd's network stream, they could still generate their own self-signed cert and bypass TLS promises. IMHO it could give a false sense of security. It would be great to be able to specify which CA certs are accepted (on top of what's in system truststore).

• ☝️ tracking ticket for that is in Add a new option TLSCertPath fluent/fluent-logger-golang#112

So, wondering if it was intentionally left undocumented (because of that), or if it's something we should (somewhere?) call out in the docs, in case users try to use the option and run into issues because of that limitation.

cc @akerouanton @vvoland for thoughts

Yes, looks like you can't verify self-signed cert.
You can still use your private CA trusted by your host and sign the certificate with it, then Docker will be able to verify it against your host CA bundle. (You need to restart docker to reread updated bundle)
https://docs.fluentd.org/plugin-helper-overview/api-plugin-helper-server#tls-configuration-basic-examples

[thaJeztah]

Thanks! Yes, so sounds like it may be a good idea to have some warning / note / callout to outline the limitations / caveats. That way the user can make a more well-informed decision whether that's acceptable for their use.

At least, I generally prefer not trying to shove such things under the rug (even if they're ugly)

Suggestions for that definitely welcome! Also /cc @ArthurFlag (in case you have any! ❤️ )