Hello! On Sun, Nov 25, 2018 at 02:49:12PM -0800, David Coles wrote:
> Hi Maxim. Thanks for your comments. > > On Sat, Nov 24, 2018 at 4:35 AM Maxim Dounin <mdou...@mdounin.ru> wrote: > > No, thank you. This change makes nginx startup unconditionally > > dependant on the DNS availability. This is not something we are > > going to accept. > > That's reasonable. I based this behaviour off `hostname -f` which also > uses `gethostbyname` for resolving the FQDN. > Note, on most systems this doesn't trigger an actual DNS lookup > provided that hosts canonical name (usually the FQDN) is configured in > `/etc/hosts` (See paragraph 5 of THE FQDN > <https://manpages.debian.org/testing/hostname/hostname.1.en.html>). The "no DNS lookup on most systems" is not something we can rely on. > On some systems `gethostent` can be used to explicitly walk > `/etc/hosts`, but behaviour is so inconsistent I would avoid it. Trying to use /etc/hosts will lead to results different from results of normal name resolution, so this doesn't looks like an option. > How would you feel about trying to resolve the FQDN at nginx startup > and, if unavailable falling back to `$hostname`? This matches the > behaviour of other languages (e.g. Python's `socket.getfqdn()` > <https://docs.python.org/3/library/socket.html#socket.getfqdn>). Even trying to resolve the FQDN will imply DNS dependency. If DNS is not availble it will wait for a timeout to expire before proceeding any further. > I could also make this a runtime evaluation, but it would be nice to > only evaluate once as it would often be used in hot paths like logging > and tracing. Using system resolver at runtime is basically not possible, because there is no non-blocking interface to system resolver, and using blocking one will will block the whole worker process during name resolution - which can take significant time. That's basically why nginx has resolver in it. The only option I see is doing name resolution only conditionally, either when requested by a configuration directive, or when the variable is actually used in the configuration. But I don't think this worth the effort - configuring appropriate hostname and/or using the name directly in nginx configuration would be a better idea. [...] > Linux in particular seems to have interpreted `gethostname` as > returning a DNS label (maximum of 63 characters) rather than a full > DNS name (up to 213 characters). > Thus it's impossible to represent certain DNS names as the system hostname. There is more than one Linux distribution, and Debian is just one of them. There are others which use FQDN: https://serverfault.com/questions/331936/setting-the-hostname-fqdn-or-short-name Note well that Debian can use FQDN as well, and "hostname -f" is smart enough to use such name without looking further. While length restrictions might make it impossible to represent some names, this is unlikely a practical problem. -- Maxim Dounin http://mdounin.ru/ _______________________________________________ nginx-devel mailing list nginx-devel@nginx.org http://mailman.nginx.org/mailman/listinfo/nginx-devel
