Subject: Re: How to configure client-side TLS ciphers for streaming replication?

From: Laurenz Albe <[email-masked]>
Date: Tue, 26 Aug 2025 14:16:58 +0200

On Tue, 2025-08-26 at 19:48 +0800, xx Z wrote:
> Is there a way for a streaming replication standby (client) to restrict its list
> of supported TLS ciphers, similar to how the ssl_ciphers parameter works on the
> primary server?
> We need this for security compliance but can't find an equivalent setting for
> the client-side connection in primary_conninfo.

I don't think that there is a way to do that on the client side.
But the streaming replication primary is surely under your control, so it should
be sufficient to set "ssl_siphers" there.

Yours,
Laurenz Albe

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From: xx Z <[email-masked]>
Date: Tue, 26 Aug 2025 20:34:59 +0800

Thanks for your suggestion.
But I still want to know why we can't set "ssl_ciphers" on the client side.
This is still considered a security issue in some cases, and PostgreSQL has
mature capabilities on the master side to implement this functionality.

Greetings,
Yunfei Zhou