From ac1c60fd9c63dd9ac4bab7e9a9f24fb347a5fbdf Mon Sep 17 00:00:00 2001
From: Christopher Faulet <cfaulet@haproxy.com>
Date: Mon, 26 Oct 2020 10:31:17 +0100
Subject: [PATCH] BUG/MINOR: server: Set server without addr but with dns in
 RMAINT on startup

On startup, if a server has no address but the dns resolutions are configured,
"none" method is added to the default init-addr methods, in addition to "last"
and "libc". Thus on startup, this server is set to RMAINT mode if no address is
found. It is only performed if no other init-addr method is configured.

Setting the RMAINT mode on startup is important to inhibit the health checks.

For instance, following servers will now be set to RMAINT mode on startup :

  server srv nofound.tld:80 check resolvers mydns
  server srv _http._tcp.service.local check resolvers mydns
  server-template srv 1-3 _http._tcp.service.local check resolvers mydns

while followings ones will trigger an error :

  server srv nofound.tld:80 check
  server srv nofound.tld:80 check resolvers mydns init-addr libc
  server srv _http._tcp.service.local check
  server srv _http._tcp.service.local check resolvers mydns init-addr libc
  server-template srv 1-3 _http._tcp.service.local check resolvers mydns init-addr libc

This patch must be backported as far as 1.8.
---
 src/server.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/src/server.c b/src/server.c
index 5ea6ca12c..4b7d7d75b 100644
--- a/src/server.c
+++ b/src/server.c
@@ -4070,14 +4070,24 @@ static int srv_apply_lastaddr(struct server *srv, int *err_code)
 /* returns 0 if no error, otherwise a combination of ERR_* flags */
 static int srv_iterate_initaddr(struct server *srv)
 {
+	char *name = srv->hostname;
 	int return_code = 0;
 	int err_code;
 	unsigned int methods;
 
+	/* If no addr and no hostname set, get the name from the DNS SRV request */
+	if (!name && srv->srvrq)
+		name = srv->srvrq->name;
+
 	methods = srv->init_addr_methods;
-	if (!methods) { // default to "last,libc"
+	if (!methods) {
+		/* otherwise default to "last,libc" */
 		srv_append_initaddr(&methods, SRV_IADDR_LAST);
 		srv_append_initaddr(&methods, SRV_IADDR_LIBC);
+		if (srv->resolvers_id) {
+			/* dns resolution is configured, add "none" to not fail on startup */
+			srv_append_initaddr(&methods, SRV_IADDR_NONE);
+		}
 	}
 
 	/* "-dr" : always append "none" so that server addresses resolution
@@ -4110,7 +4120,7 @@ static int srv_iterate_initaddr(struct server *srv)
 			srv_set_admin_flag(srv, SRV_ADMF_RMAINT, NULL);
 			if (return_code) {
 				ha_warning("parsing [%s:%d] : 'server %s' : could not resolve address '%s', disabling server.\n",
-					   srv->conf.file, srv->conf.line, srv->id, srv->hostname);
+					   srv->conf.file, srv->conf.line, srv->id, name);
 			}
 			return return_code;
 
@@ -4118,7 +4128,7 @@ static int srv_iterate_initaddr(struct server *srv)
 			ipcpy(&srv->init_addr, &srv->addr);
 			if (return_code) {
 				ha_warning("parsing [%s:%d] : 'server %s' : could not resolve address '%s', falling back to configured address.\n",
-					   srv->conf.file, srv->conf.line, srv->id, srv->hostname);
+					   srv->conf.file, srv->conf.line, srv->id, name);
 			}
 			goto out;
 
@@ -4129,11 +4139,11 @@ static int srv_iterate_initaddr(struct server *srv)
 
 	if (!return_code) {
 		ha_alert("parsing [%s:%d] : 'server %s' : no method found to resolve address '%s'\n",
-		      srv->conf.file, srv->conf.line, srv->id, srv->hostname);
+		      srv->conf.file, srv->conf.line, srv->id, name);
 	}
 	else {
 		ha_alert("parsing [%s:%d] : 'server %s' : could not resolve address '%s'.\n",
-		      srv->conf.file, srv->conf.line, srv->id, srv->hostname);
+		      srv->conf.file, srv->conf.line, srv->id, name);
 	}
 
 	return_code |= ERR_ALERT | ERR_FATAL;
@@ -4165,7 +4175,7 @@ int srv_init_addr(void)
 			goto srv_init_addr_next;
 
 		for (srv = curproxy->srv; srv; srv = srv->next)
-			if (srv->hostname)
+			if (srv->hostname || srv->srvrq)
 				return_code |= srv_iterate_initaddr(srv);
 
  srv_init_addr_next: