tree ec39bf37c61706b932d892481332983de90ddf75
parent 8ea0bcc911809e77560bdd937c02a0b832526ef7
author Baptiste Assmann <bedis9@gmail.com> 1495459035 +0200
committer Willy Tarreau <w@1wt.eu> 1496397534 +0200
encoding latin1

MAJOR/REORG: dns: DNS resolution task and requester queues

This patch is a major upgrade of the internal run-time DNS resolver in
HAProxy and it brings the following 2 main changes:

1. DNS resolution task

Up to now, DNS resolution was triggered by the health check task.
From now, DNS resolution task is autonomous. It is started by HAProxy
right after the scheduler is available and it is woken either when a
network IO occurs for one of its nameserver or when a timeout is
matched.

From now, this means we can enable DNS resolution for a server without
enabling health checking.

2. Introduction of a dns_requester structure

Up to now, DNS resolution was purposely made for resolving server
hostnames.
The idea, is to ensure that any HAProxy internal object should be able
to trigger a DNS resolution. For this purpose, 2 things has to be done:
  - clean up the DNS code from the server structure (this was already
    quite clean actually) and clean up the server's callbacks from
    manipulating too much DNS resolution
  - create an agnostic structure which allows linking a DNS resolution
    and a requester of any type (using obj_type enum)

3. Manage requesters through queues

Up to now, there was an uniq relationship between a resolution and it's
owner (aka the requester now). It's a shame, because in some cases,
multiple objects may share the same hostname and may benefit from a
resolution being performed by a third party.
This patch introduces the notion of queues, which are basically lists of
either currently running resolution or waiting ones.

The resolutions are now available as a pool, which belongs to the resolvers.
The pool has has a default size of 64 resolutions per resolvers and is
allocated at configuration parsing.