From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTP id C1D995A0082 for ; Wed, 25 Jan 2023 18:55:28 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674669327; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EBOld4r+wxvCatWFhxrnZyvivtDYW75UOZ3dpZYoIck=; b=DZvK7WJmEhJ+EiGhTus5XxjXruJvqngI8d4fQZHPC3pkDvUwC7rlqP3gcx9GYwBeI8eOFd EmkyZj6zQDTjJ9KTXBsmMdoRdwFJ9c+ZexCIbrgEldqc+NrB3ZC7QVDfVFy05Vh0SYQezI +AE1dxRvaKsCMqdw68hvcq25+sWzpSw= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-609-Z5AV6rJ4Nca1vwlYXnYoMg-1; Wed, 25 Jan 2023 12:55:26 -0500 X-MC-Unique: Z5AV6rJ4Nca1vwlYXnYoMg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DC8F88533B6; Wed, 25 Jan 2023 17:55:25 +0000 (UTC) Received: from maya.cloud.tilaa.com (ovpn-208-4.brq.redhat.com [10.40.208.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 80C9F2166B26; Wed, 25 Jan 2023 17:55:25 +0000 (UTC) Date: Wed, 25 Jan 2023 18:55:06 +0100 From: Stefano Brivio To: Noah Gold Subject: Re: Improved handling of changing DNS resolvers Message-ID: <20230125185506.7b5462ca@elisabeth> In-Reply-To: References: <20230121104703.3ebcc753@elisabeth> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: B4KYCVDXQ5LOFRQGI7ICNLMH4J4LPUGR X-Message-ID-Hash: B4KYCVDXQ5LOFRQGI7ICNLMH4J4LPUGR X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: David Gibson , passt-dev@passt.top X-Mailman-Version: 3.3.3 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Mon, 23 Jan 2023 17:20:13 +1100 David Gibson wrote: > On Sat, Jan 21, 2023 at 10:47:03AM +0100, Stefano Brivio wrote: > > Hi Noah, > > > > Sorry for the delay, I didn't check pending mailing list posts for a > > couple of days. Comments below: > > > > On Tue, 17 Jan 2023 11:50:50 -0800 > > Noah Gold wrote: > > > > > Hi folks, > > > > > > libslirp and Passt have different approaches to sharing DNS resolvers with > > > the guest system, each with their own benefits & drawbacks. On the libslirp > > > project, we're discussing [1] how to support DNS failover. Passt already has > > > support for this, but there is a drawback to its solution which prevents us > > > from taking a similar approach: the resolvers are read exactly once, so if the > > > host changes networks at runtime, the guest will not receive the updated > > > resolvers and thus its connectivity will break. > > So, passt/pasta kinda-sorta binds itself to a particular host > interface, so DNS won't be the only issue if the host changes > network. For one thing, at least by default the guest gets the same > IP as the host, so if the host IP changes the guest will get out of > sync. We'll mostly cope with that ok, but there will be some edge > cases which will break (most obviously if after the network change the > guest wants to talk to something at the host's old address / its > current address). Noah, by the way, if your usage for DNS failover is related to a virtual machine being migrated to another host with different addressing, mind that you could simply tell qemu to connect to a new instance of passt. That's something you can't do with libslirp. Would that solve your problem, or your issue is specifically related to DNS failover without any VM migration playing a role? -- Stefano