[PATCH 2 of 2] The "sort=" parameter of the "resolver" directive

[Maxim Dounin]

Hello!

On Tue, Jun 28, 2022 at 08:25:36PM +0400, Sergey Kandaurov wrote:

> # HG changeset patch
> # User Ruslan Ermilov <ru at nginx.com>
> # Date 1645589387 -10800
> #      Wed Feb 23 07:09:47 2022 +0300
> # Node ID e80adbf788f6796c6bdf415938abb19b7aa43e3e
> # Parent  04e314eb6b4d20a48c5d7bab0609e1b03b51b406
> The "sort=" parameter of the "resolver" directive.

As already noted, should be "prefer=".

> 
> diff -r 04e314eb6b4d -r e80adbf788f6 src/core/ngx_resolver.c
> --- a/src/core/ngx_resolver.c	Wed Feb 23 07:08:37 2022 +0300
> +++ b/src/core/ngx_resolver.c	Wed Feb 23 07:09:47 2022 +0300
> @@ -227,6 +227,7 @@ ngx_resolver_create(ngx_conf_t *cf, ngx_
>          }
>  
>  #if (NGX_HAVE_INET6)
> +
>          if (ngx_strncmp(names[i].data, "ipv4=", 5) == 0) {
>  
>              if (ngx_strcmp(&names[i].data[5], "on") == 0) {
> @@ -260,6 +261,24 @@ ngx_resolver_create(ngx_conf_t *cf, ngx_
>  
>              continue;
>          }
> +
> +        if (ngx_strncmp(names[i].data, "prefer=", 7) == 0) {
> +
> +            if (ngx_strcmp(&names[i].data[7], "ipv4") == 0) {
> +                r->prefer = NGX_RESOLVE_PREFER_A;
> +
> +            } else if (ngx_strcmp(&names[i].data[7], "ipv6") == 0) {
> +                r->prefer = NGX_RESOLVE_PREFER_AAAA;
> +
> +            } else {
> +                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
> +                                   "invalid parameter: %V", &names[i]);
> +                return NULL;
> +            }
> +
> +            continue;
> +        }
> +
>  #endif
>  
>          ngx_memzero(&u, sizeof(ngx_url_t));
> @@ -4250,7 +4269,27 @@ ngx_resolver_export(ngx_resolver_t *r, n
>      }
>  
>      i = 0;
> -    d = rotate ? ngx_random() % n : 0;
> +
> +    switch (r->prefer) {
> +
> +#if (NGX_HAVE_INET6)
> +    case NGX_RESOLVE_PREFER_A:
> +        d = 0;
> +        break;
> +
> +    case NGX_RESOLVE_PREFER_AAAA:
> +        d = rn->naddrs6;
> +
> +        if (d == n) {
> +            d = 0;
> +        }
> +
> +        break;
> +#endif
> +
> +    default:
> +        d = rotate ? ngx_random() % n : 0;
> +    }

With this code, a configuration like this:

    resolver ... prefer=ipv4;
    set $foo "";
    proxy_pass http://example.com$foo;

will result in only IPv4 addresses being used assuming successful 
connections, and IPv6 addresses being used only as a backup.  This 
looks quite different from the current behaviour, as well as from 
what we do with

    proxy_pass http://example.com;

when using system resolver.

Not sure we want to introduce such behaviour.  While it might be 
closer to what RFC 6724 recommends for clients, it is clearly not 
in line with how we handle multiple upstream addresses in general, 
and certainly will confuse users.  If we want to introduce this, 
it probably should be at least consistent within resolver vs. 
system resolver cases.

>  
>      if (rn->naddrs) {
>          j = rotate ? ngx_random() % rn->naddrs : 0;
> diff -r 04e314eb6b4d -r e80adbf788f6 src/core/ngx_resolver.h
> --- a/src/core/ngx_resolver.h	Wed Feb 23 07:08:37 2022 +0300
> +++ b/src/core/ngx_resolver.h	Wed Feb 23 07:09:47 2022 +0300
> @@ -36,6 +36,9 @@
>  
>  #define NGX_RESOLVER_MAX_RECURSION    50
>  
> +#define NGX_RESOLVE_PREFER_A          1
> +#define NGX_RESOLVE_PREFER_AAAA       2
> +
>  
>  typedef struct ngx_resolver_s  ngx_resolver_t;
>  
> @@ -175,6 +178,8 @@ struct ngx_resolver_s {
>      ngx_queue_t               srv_expire_queue;
>      ngx_queue_t               addr_expire_queue;
>  
> +    unsigned                  prefer:2;
> +
>      unsigned                  ipv4:1;
>  
>  #if (NGX_HAVE_INET6)

-- 
Maxim Dounin
http://mdounin.ru/