Subject: Re: Feature request: A method to configure client-side TLS ciphers for streaming replication

From: Ron Johnson <[email-masked]>
Date: Tue, 26 Aug 2025 08:59:39 -0400

On Tue, Aug 26, 2025 at 3:28 AM xx Z <[email-masked]> wrote:

> Hello PostgreSQL community,
>
> I have a question regarding the configuration of streaming replication.
>
> When setting up streaming replication over TLS, I've noticed that while
> the primary server can restrict its supported encryption algorithms using
> the ssl_ciphers parameter, there doesn't seem to be a corresponding method
> for the standby (client) side of the replication connection. The standby
> appears to use all the default ciphers supported by the system's OpenSSL
> library.
>

What is a "standby (client)"?

Postgresql version: 15.2

That's missing 12 sets (three years) of bug fixes.  When using RPM or .deb
packages, updating takes only a few minutes.

-- 
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!

---

From: xx Z <[email-masked]>
Date: Tue, 26 Aug 2025 21:09:36 +0800

Hello,
Thank you for the reply and for the advice about our PostgreSQL version. We
will plan to update it.
To clarify what I meant by "standby (client)": In a streaming replication
setup, the standby server connects to the primary server to receive data.
In this specific network connection, the standby acts as the client, and
the primary acts as the server. My question is about restrict thr lists of
supported TLS ciphers on the standby (the client side of the connection).
Regarding my original question, does the latest version of PostgreSQL
provide a way to configure the client-side TLS cipher list for the
replication connection? If not, are there any discussions or plans to add
this feature in the future?
Thank you for your help.
Best regards,
Yunfei Zhou

---

From: Ron Johnson <[email-masked]>
Date: Tue, 26 Aug 2025 14:43:46 -0400

On Tue, Aug 26, 2025 at 9:09 AM xx Z <[email-masked]> wrote:

> Hello,
> Thank you for the reply and for the advice about our PostgreSQL version.
> We will plan to update it.
> the primary acts as the server.
>

I think you are using non-standard terminology.

> My question is about restrict thr lists of supported TLS ciphers on the
> standby (the client side of the connection).

That's the responsibility of your ssl configuration, I think.

https://www.postgresql.org/message-id/39BE74F7-903A-467F-AA15-E7062361A8E2%40yesql.se

>> That's missing 12 sets (three years) of bug fixes.  When using RPM or
>> .deb packages, updating takes only a few minutes.
>>
>