Hi Neil
Thank you for sharing your perspectives.
TTL-based DNS re-resolving is planned for this feature.
Also, nginx resolver (which we plan to use) supports "ipv6=off" and
(since 1.23.1) "ipv4=off" parameters for cases when IPv6 or IPv4 addresses
are not desired.
We know about solutions based on Lua. However, the motivation is to provide
a solution that works out of the box.
--
Vladimir Kokshenev
On 7/21/22, 6:02 AM, "Neil Craig" <neil.cr...@bbc.co.uk> wrote:
EXTERNAL MAIL: neil.cr...@bbc.co.uk
Hi Vladimir
I hope you don't mind me chipping in here.
We currently have 2 services which use Nginx with upstreams whose DNS can
change frequently (e.g. AWS S3, ELB/ALB origins) so we're familiar with this
problem. Initially we did a config reload every minute to solve the issue but
since then, we've created custom Lua (using the OpenResty Lua module) to
achieve the same thing in a more efficient way.
What you're proposing sounds great to me. I wanted to suggest a few feature
ideas for your consideration:
* DNS TTL-based refresh (rather than refreshing every N seconds)
* DNS prefresh (update DNS when the elapsed time since the last refresh is
perhaps 90% of the TTL)
* IPv4/6 ignore (useful for example when there's a v6 IP available but the
system/network doesn't support v6)
Cheers
Neil Craig (He/Him)
Lead Architect, BBC Digital Distribution
On 20/07/2022, 20:09, "Vladimir Kokshenev via nginx-devel"
<nginx-devel@nginx.org> wrote:
Hello!
This is the two-part proposal to open-source periodic upstream server
resolution
and implement a dedicated service worker for nginx. The purpose of this
e-mail
is to describe the WHY and solicit feedback.
Nginx supports domain names in the upstream server configuration.
Currently, domain names are resolved at configuration time only,
and there are no subsequent name resolutions.
There are plans to open-source re-resolvable upstream servers.
This will allow applying DNS updates to upstream configurations in
runtime.
So, there is a need to support periodic asynchronous operations.
And a dedicated service worker is a possible architectural way to
address this.
The master process reads and parses configuration and creates the
service worker
when needed (in a similar way to cache-related processes).
The service worker manages periodic name resolutions and updates
corresponding
upstream configurations. The name resolution relies on the existing
nginx
resolver and upstream zone functionality.
The service worker will be responsible solely for periodic background
tasks
and wouldn't accept client connections.
The service worker should be the last worker process to shut down
to maintain the actual state of upstreams when there are active workers.
Alternative architecture considered was about choosing one of the
regular
workers (e.g., worker zero) to take care of periodic upstream server
resolution,
but it creates asymmetry in responsibilities and load for this
dedicated worker.
--
Vladimir Kokshenev
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