nsqd: refresh the address of nsqlookupd on DNS changes

[danbf]

right now an nsqd client doesn't refresh it's ip connections to lookupd on lookupd DNS changes. this causes a problem on long running instances when a lookupd instance gets rebuilt.

[starsz]

Hello，I think you can config the lookupd address by using IP.
When a lookupd instance gets rebuilt, you can update by using
PUT /config/nsqlookupd_tcp_addresses interface.

See nsq doc https://nsq.io/components/nsqd.html#put-confignsqlookupd_tcp_addresses.

[mreiferson]

Agreed, although @starsz points out a workaround, I think it's a reasonable expectation that if you use DNS to provide some operational control over nsqlookupd deployments that it should generally work as expected.

[starsz]

Aha，@mreiferson I think I can contribute to this project. : )

[mreiferson]

@starsz please do!