Enable http3 for a subset of domains

Thu Jun 27 06:17:22 UTC 2024

> On 26 Jun 2024, at 17:56, Roman Arutyunyan <arut at nginx.com> wrote:
> 
> Hi,
> 
>> On 26 Jun 2024, at 7:21 PM, Riccardo Brunetti Host <riccardo.brunetti at host.it> wrote:
>> 
>> Hello, thanks for the answer.
>> 
>>> On 26 Jun 2024, at 16:45, Roman Arutyunyan <arut at nginx.com <mailto:arut at nginx.com>> wrote:
>>> 
>>> Hi,
>>> 
>>>> On 26 Jun 2024, at 6:15 PM, Riccardo Brunetti Host <riccardo.brunetti at host.it <mailto:riccardo.brunetti at host.it>> wrote:
>>>> 
>>>> Hello.
>>>> 
>>>> I have a Nginx server which acts as a reverse proxy for a given number of different domains and I’m trying to enable http3 for a subset of them.
>>>> 
>>>> I placed the directives:
>>>> 
>>>>>     http3 on;
>>>>>     listen xx.xx.xx.xx:443 default_server quic reuseport;
>>>>>     quic_retry on;
>>>> 
>>>> in the default.conf file and then, only for those domains which I want http3 enabled I also add in the corresponding virtual host:
>>>> 
>>>>>         http3 on;
>>>>>         listen xx.xx.xx.xx:443 quic;
>>>>>         quic_retry on;
>>>> 
>>>> In the server section and 
>>>> 
>>>>> add_header Alt-Svc 'h3=":8443"; ma=86400';
>>>> 
>>>> Inside the location.
>>>> 
>>>> Now, what happens is that if I try to open the sites *with* http3 enabled, everything works as expected. If I try to open a site *without* http3 enabled, sometimes I have an SSL error because the server returns the “default virtual host” certificate.
>>>> It seems related to the type of browser.
>>>> 
>>>> Is it an expected behaviour or I am doing something wrong with the server configuration?
>>> 
>>> If you use http/3 to access a virtual server that does not support http/3, the default http/3 server will be used.
>>> 
>>> Make sure the above add_header does not affect the servers which do not support http/3.
>> 
>> I add the header above only on the virtual hosts which I want to support http/3, thus it should not interfere with the other non http/3 domains.
>> Nevertheless, if I try with curl:
>> 
>> 1) Site http/3 enabled:
>> 
>>> # curl --http3 -I -v https://<fqdn>
>>> * Host <fqdn>t:443 was resolved.
>>> * IPv6: (none)
>>> * IPv4: <ip>
>>> * WARNING: no socket in pollset, transfer may stall!
>>> *   Trying <ip>:443...
>>> * Server certificate:
>>> *  subject: CN=<fqdn>
>>> *  start date: May 14 07:39:37 2024 GMT
>>> *  expire date: Aug 12 07:39:36 2024 GMT
>>> *  subjectAltName: host “<fqdn>" matched cert's “<fqdn>"
>>> *  issuer: C=US; O=Let's Encrypt; CN=R3
>>> *  SSL certificate verify ok.
>>> * Connected to <fqdn> (<ip>) port 443
>>> * using HTTP/3
>>> * [HTTP/3] [0] OPENED stream for https://<fqdn>/
>> …
>> …
>> 
>> So it gets the correct certificate and it goes on using http/3
>> 
>> 2) Site non http/3 enabled:
>> 
>>> # curl --http3 -I -v https://<fqdn>
>> 
>>> * Host <fqdn>:443 was resolved.
>>> * IPv6: (none)
>>> * IPv4: <ip>
>>> * WARNING: no socket in pollset, transfer may stall!
>>> *   Trying <ip>:443...
>>> * SSL certificate problem: unable to get local issuer certificate
>>> * connect to <ip> port 443 failed: SSL peer certificate or SSH remote key was not OK
>>> * Failed to connect to<fqdn> port 443 after 33 ms: SSL peer certificate or SSH remote key was not OK
>>> *   Trying <ip>:443...
>>> * Connected to<fqdn> (<ip>) port 443
>>> * ALPN: curl offers h2,http/1.1
>>> * TLSv1.2 (OUT), TLS handshake, Client hello (1):
>>> * TLSv1.2 (IN), TLS handshake, Server hello (2):
>>> * TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
>>> * TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
>>> * TLSv1.3 (IN), TLS handshake, Certificate (11):
>>> * TLSv1.3 (IN), TLS handshake, CERT verify (15):
>>> * TLSv1.3 (IN), TLS handshake, Finished (20):
>>> * TLSv1.3 (OUT), TLS handshake, Finished (20):
>>> * SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384 / [blank] / UNDEF
>>> * ALPN: server accepted h2
>>> * Server certificate:
>>> *  subject: CN=<fqdn>
>>> *  start date: Apr 16 08:36:25 2024 GMT
>>> *  expire date: Jul 15 08:36:24 2024 GMT
>>> *  subjectAltName: host "<fqdn>" matched cert's "<fqdn>"
>>> *  issuer: C=US; O=Let's Encrypt; CN=R3
>>> *  SSL certificate verify ok.
>>> * using HTTP/2
>>> * [HTTP/2] [1] OPENED stream for https://<fqdn>/
>> 
>> 
>> So it tries with http/3, gets a wrong certificate (the server default one), then it switches to http/2 and goes on. 
>> The first attempt with http/3 probably gives problems with some browsers?
>> If this is the case, is there a way to avoid this or should I simply configure http/3 on all domains?
> 
> Why would you (or client) connect to an http/3 port for a server which does not support http/3?
> What would be your expectation in this case? The same will happen for http/1 and http/2 as well.
> You can connect to an http/1 ssl port, request a missing server and receive a default server certificate.
> It's just there is no fallback for http/1 and client will just give up.
> 
> The add_header suggests that http/3 is supported for a certain server.
> It should not be sent for servers which do not support http/3, and clients should not use http/3 for them.

I agree with you, mine was an example just to show with curl what seems to happen with some browsers.
It seems to me that they try http/3 even if the server doesn’t advertise the header and then stop because of the error on the certificate.
I don’t know if this is something known.
Anyway, I think I will bypass this by enabling http/3 on all sites.

Thanks a lot for you help

Riccardo 

> 
>>> If it does, this will mislead clients by offering them to switch to unsupported http/3.
>>> 
>>>> Nginx version: nginx/1.26.1 on ubuntu 22.04
>>>> 
>>>> Thanks.
>>>> Riccardo
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>>> 
>>> ----
>>> Roman Arutyunyan
>>> arut at nginx.com <mailto:arut at nginx.com>
>>> 
>> 
>> Riccardo
>> 
>>> 
>>> 
>>> 
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>> 
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> ----
> Roman Arutyunyan
> arut at nginx.com
> 
> 
> 
> 
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