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BUG/MINOR: dns: add tempo between 2 connection attempts for dns servers

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As reported by Lukas Tribus on the mailing list [1], trying to connect to
a nameserver with invalid network settings causes haproxy to retry a new
connection attempt immediately which eventually causes unexpected CPU usage
on the thread responsible for the applet (namely 100% on one CPU will be
observed).

This can be reproduced with the test config below:

 resolvers default
  nameserver ns1 tcp4@8.8.8.8:53 source 192.168.99.99
 listen listen
  mode http
  bind :8080
  server s1 www.google.com resolvers default init-addr none

To fix this the issue, we add a temporisation of one second between a new
connection attempt is retried. We do this in dns_session_create() when we
know that the applet was created in the release callback (when previous
query attempt was unsuccessful), which means initial connection is not
affected.

[1]: https://www.mail-archive.com/haproxy@formilux.org/msg45665.html

This should fix GH #2909 and may be backported to all stable versions.
This patch depends on ("MINOR: applet: add appctx_schedule() macro")
This commit is contained in:
Aurelien DARRAGON 2025-04-29 20:13:00 +02:00
parent 1ced5ef2fd
commit 27236f2218
1 changed files with 13 additions and 7 deletions
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20
src/dns.c
View File

@ -806,7 +806,7 @@ void dns_session_free(struct dns_session *ds)
pool_free(dns_session_pool, ds);
}
static struct appctx *dns_session_create(struct dns_session *ds);
static struct appctx *dns_session_create(struct dns_session *ds, int tempo);
static int dns_session_init(struct appctx *appctx)
{
@ -912,7 +912,7 @@ static void dns_session_release(struct appctx *appctx)
/* Create a new appctx, We hope we can
* create from the release callback! */
ds->appctx = dns_session_create(ds);
ds->appctx = dns_session_create(ds, 1);
if (!ds->appctx) {
dns_session_free(ds);
HA_SPIN_UNLOCK(DNS_LOCK, &dss->lock);
@ -937,8 +937,10 @@ static struct applet dns_session_applet = {
/*
* Function used to create an appctx for a DNS session
* It sets its context into appctx->svcctx.
* if <tempo> is set, then the session startup will be delayed by 1
* second
*/
static struct appctx *dns_session_create(struct dns_session *ds)
static struct appctx *dns_session_create(struct dns_session *ds, int tempo)
{
struct appctx *appctx;
@ -947,10 +949,14 @@ static struct appctx *dns_session_create(struct dns_session *ds)
goto out_close;
appctx->svcctx = (void *)ds;
if (appctx_init(appctx) == -1) {
ha_alert("out of memory in dns_session_create().\n");
goto out_free_appctx;
if (!tempo) {
if (appctx_init(appctx) == -1) {
ha_alert("out of memory in dns_session_create().\n");
goto out_free_appctx;
}
}
else
appctx_schedule(appctx, tick_add(now_ms, MS_TO_TICKS(1000)));
return appctx;
@ -1072,7 +1078,7 @@ struct dns_session *dns_session_new(struct dns_stream_server *dss)
ds->task_exp->process = dns_process_query_exp;
ds->task_exp->context = ds;
ds->appctx = dns_session_create(ds);
ds->appctx = dns_session_create(ds, 0);
if (!ds->appctx)
goto error;