DNS query timeout

[shuhei]

Give up when DNS server doesn't reply or the answer datagram is lost.

[shuhei]

Some research on dns.resolve family functions.

Timeout

There is no way to change the timeout of dns.resolve functions. The timeout seems to be the default timeout of ares_init_options, which is 5 seconds. And it retries 3 more times (4 tries in total).

Cancel

There is no way to cancel outstanding DNS queries except Resolver#cancel(), which cancels the all outstanding queries on the Resolver.

Does it make sense to create a Resolver for each hostname and cancel the outstanding DNS request? I'm not sure whether it's useful to cancel outstanding requests when retrying with a timeout in the first place though.

[vigneshshanmugam]

Since the code is on the userland and Wont a simple setTimeout handler work? As you suggested, each hostname would get a Resolver and we can keep calling cancel on the resolver handle when we run out of retries and timeouts.

Not really sure, how much it would affect the performance though.

[shuhei]

For now, I don't see any big issues with only the default timeout of c-ares yet. One possible case is faster retry with a shorter timeout, but pollen keeps previous IP addresses even if DNS queries fail...

[vigneshshanmugam]

Agreed on the faster retry part.

but pollen keeps previous IP addresses even if DNS queries fail.

This will be an issue if the traffic switch was aggressive(100% to new stack) and old stack deleted due to a serious bug.

[shuhei]

Good point. To address it, we also need a shorter polling interval.