The ANY query type is weird, and some resolvers don't 'do the legwork' of resolving useful things like CNAMEs. Given that upstream resolver behavior is not always under the control of the HAProxy administrator, we should not use the ANY query type. Rather, we should use A or AAAA according to either the explicit preferences of the operator, or the implicit default (AAAA/IPv6).
- Andrew Hayworth
>From 8ed172424cbd79197aacacd1fd89ddcfa46e213d Mon Sep 17 00:00:00 2001
From: Andrew Hayworth <andrew.haywo...@getbraintree.com>
Date: Mon, 19 Oct 2015 22:29:51 +0000
Subject: [PATCH] MEDIUM: dns: Don't use the ANY query type
Basically, it's ill-defined and shouldn't really be used going forward.
We can't guarantee that resolvers will do the 'legwork' for us and
actually resolve CNAMES when we request the ANY query-type. Case in point
(obfuscated, clearly):
PRODUCTION! ahaywo...@secret-hostname.com:~$
dig @10.11.12.53 ANY api.somestartup.io
; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> @10.11.12.53 ANY api.somestartup.io
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62454
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 0
;; QUESTION SECTION:
;api.somestartup.io. IN ANY
;; ANSWER SECTION:
api.somestartup.io. 20 IN CNAME
api-somestartup-production.ap-southeast-2.elb.amazonaws.com.
;; AUTHORITY SECTION:
somestartup.io. 166687 IN NS ns-1254.awsdns-28.org.
somestartup.io. 166687 IN NS ns-1884.awsdns-43.co.uk.
somestartup.io. 166687 IN NS ns-440.awsdns-55.com.
somestartup.io. 166687 IN NS ns-577.awsdns-08.net.
;; Query time: 1 msec
;; SERVER: 10.11.12.53#53(10.11.12.53)
;; WHEN: Mon Oct 19 22:02:29 2015
;; MSG SIZE rcvd: 242
HAProxy can't handle that response correctly.
Rather than try to build in support for resolving CNAMEs presented
without an A record in an answer section (which may be a valid
improvement further on), this change just skips ANY record types
altogether. A and AAAA are much more well-defined and predictable.
Notably, this commit preserves the implicit "Prefer IPV6 behavior."
---
include/types/dns.h | 3 ++-
src/checks.c | 6 +++++-
src/dns.c | 6 +++++-
src/server.c | 18 +++++++-----------
4 files changed, 19 insertions(+), 14 deletions(-)
diff --git a/include/types/dns.h b/include/types/dns.h
index f8edb73..ea1a9f9 100644
--- a/include/types/dns.h
+++ b/include/types/dns.h
@@ -161,7 +161,8 @@ struct dns_resolution {
unsigned int last_status_change; /* time of the latest DNS
resolution status change */
int query_id; /* DNS query ID dedicated for this resolution */
struct eb32_node qid; /* ebtree query id */
- int query_type; /* query type to send. By default DNS_RTYPE_ANY */
+ int query_type;
+ /* query type to send. By default DNS_RTYPE_A or DNS_RTYPE_AAAA
depending on resolver_family_priority */
int status; /* status of the resolution being processed RSLV_STATUS_* */
int step; /* */
int try; /* current resolution try */
diff --git a/src/checks.c b/src/checks.c
index ade2428..d3cd567 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -2214,7 +2214,11 @@ int trigger_resolution(struct server *s)
resolution->query_id = query_id;
resolution->qid.key = query_id;
resolution->step = RSLV_STEP_RUNNING;
- resolution->query_type = DNS_RTYPE_ANY;
+ if (resolution->resolver_family_priority == AF_INET) {
+ resolution->query_type = DNS_RTYPE_A;
+ } else {
+ resolution->query_type = DNS_RTYPE_AAAA;
+ }
resolution->try = resolvers->resolve_retries;
resolution->try_cname = 0;
resolution->nb_responses = 0;
diff --git a/src/dns.c b/src/dns.c
index 7f71ac7..53b65ab 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -102,7 +102,11 @@ void dns_reset_resolution(struct dns_resolution
*resolution)
resolution->qid.key = 0;
/* default values */
- resolution->query_type = DNS_RTYPE_ANY;
+ if (resolution->resolver_family_priority == AF_INET) {
+ resolution->query_type = DNS_RTYPE_A;
+ } else {
+ resolution->query_type = DNS_RTYPE_AAAA;
+ }
/* the second resolution in the queue becomes the first one */
LIST_DEL(&resolution->list);
diff --git a/src/server.c b/src/server.c
index 8ddff00..33d6922 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2692,21 +2692,13 @@ int snr_resolution_error_cb(struct
dns_resolution *resolution, int error_code)
case DNS_RESP_TRUNCATED:
case DNS_RESP_ERROR:
case DNS_RESP_NO_EXPECTED_RECORD:
- qtype_any = resolution->query_type == DNS_RTYPE_ANY;
res_preferred_afinet = resolution->resolver_family_priority ==
AF_INET && resolution->query_type == DNS_RTYPE_A;
res_preferred_afinet6 = resolution->resolver_family_priority ==
AF_INET6 && resolution->query_type == DNS_RTYPE_AAAA;
- if ((qtype_any || res_preferred_afinet || res_preferred_afinet6)
+ if ((res_preferred_afinet || res_preferred_afinet6)
|| (resolution->try > 0)) {
/* let's change the query type */
- if (qtype_any) {
- /* fallback from ANY to resolution preference */
- if (resolution->resolver_family_priority == AF_INET6)
- resolution->query_type = DNS_RTYPE_AAAA;
- else
- resolution->query_type = DNS_RTYPE_A;
- }
- else if (res_preferred_afinet6) {
+ if (res_preferred_afinet6) {
/* fallback from AAAA to A */
resolution->query_type = DNS_RTYPE_A;
}
@@ -2716,7 +2708,11 @@ int snr_resolution_error_cb(struct
dns_resolution *resolution, int error_code)
}
else {
resolution->try -= 1;
- resolution->query_type = DNS_RTYPE_ANY;
+ if (resolution->resolver_family_priority == AF_INET) {
+ resolution->query_type = DNS_RTYPE_A;
+ } else {
+ resolution->query_type = DNS_RTYPE_AAAA;
+ }
}
dns_send_query(resolution);
--
2.1.3
0001-MEDIUM-dns-Don-t-use-the-ANY-query-type.patch
Description: Binary data
