registrar/mid-registrar: Add the "expires_max_deviation" modparam

This new modparam could help mitigate the effects of post-restart "registration storms", when all TCP connections go down and a significant portion of devices re-REGISTER on the spot. By randomizing the returned expiry intervals, the REGISTER storm will no longer repeat at regular intervals following a restart, e.g. every 3600 seconds.
OpenSIPS · Mar 25, 2022 · f301667 · f301667
1 parent 9451d6c
commit f301667
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Showing 5 changed files with 84 additions and 9 deletions.
diff --git a/lib/reg/ci.c b/lib/reg/ci.c
@@ -132,8 +132,8 @@ ucontact_info_t *pack_ci(struct sip_msg* _m, contact_t* _c, unsigned int _e,
 			goto error;
 		}
 
-		/* set expire time */
-		ci.expires = _e;
+		/* set expire time, with an optional random deviation */
+		ci.expires = randomize_expires(_e);
 
 		if (pn_enable && _reg_flags & REG_SAVE__PN_ON_FLAG) {
 			ci.flags |= FL_PN_ON;

diff --git a/lib/reg/common.c b/lib/reg/common.c
@@ -20,7 +20,8 @@
 
 #include "common.h"
 
-/* modparams */
+/* common registrar modparams */
+int expires_max_deviation;  /*!< +/- max deviation for contact lifetimes */
 int max_contacts = 0;		/*!< Maximum number of contacts per AOR
                                  (0 == no checking) */
 int max_username_len = USERNAME_MAX_SIZE;
@@ -38,6 +39,18 @@ int reg_init_globals(void)
 	realm_prefix.len = strlen(realm_prefix.s);
 	rcv_param.len = strlen(rcv_param.s);
 
+	if (expires_max_deviation < 0) {
+		expires_max_deviation = -expires_max_deviation;
+		LM_ERR("'expires_max_deviation' cannot be negative, fixing to %d\n",
+		       expires_max_deviation);
+	}
+
+	if (expires_max_deviation > RAND_MAX/2) {
+		expires_max_deviation = RAND_MAX/2;
+		LM_ERR("'expires_max_deviation' is too large, fixing to %d\n",
+		       expires_max_deviation);
+	}
+
 	if (max_expires && max_expires < min_expires) {
 		LM_ERR("max_expires (%d) < min_expires (%d), "
 		       "bumping max_expires up to %d\n", max_expires,

diff --git a/lib/reg/common.h b/lib/reg/common.h
@@ -47,20 +47,48 @@ extern usrloc_api_t ul;
 extern struct tm_binds tmb;
 
 /* common registrar modparams */
+extern int expires_max_deviation;
 extern int max_contacts;
 extern int max_username_len;
 extern int max_domain_len;
 extern int max_aor_len;
 extern int max_contact_len;
 
 #define reg_modparams \
-	{"max_contacts",       INT_PARAM, &max_contacts}, \
-	{"max_username_len",   INT_PARAM, &max_username_len}, \
-	{"max_domain_len",     INT_PARAM, &max_domain_len}, \
-	{"max_aor_len",        INT_PARAM, &max_aor_len}, \
-	{"max_contact_len",    INT_PARAM, &max_contact_len}
+	{"max_contacts",          INT_PARAM, &max_contacts}, \
+	{"max_username_len",      INT_PARAM, &max_username_len}, \
+	{"max_domain_len",        INT_PARAM, &max_domain_len}, \
+	{"max_aor_len",           INT_PARAM, &max_aor_len}, \
+	{"max_contact_len",       INT_PARAM, &max_contact_len}, \
+	{"expires_max_deviation", INT_PARAM, &expires_max_deviation}
 
 /* common registrar init code */
 int reg_init_globals(void);
 
+static inline time_t randomize_expires(unsigned int expires_ts)
+{
+	time_t ret;
+
+	if (!expires_max_deviation)
+		return expires_ts;
+
+	int expires_dur = expires_ts - get_act_time();
+	int expires_adj = rand() % (expires_max_deviation * 2 + 1)
+						- expires_max_deviation;
+
+	expires_dur += expires_adj;
+	if (expires_dur < min_expires)
+		expires_dur = min_expires;
+
+	if (max_expires && expires_dur > max_expires)
+		expires_dur = max_expires;
+
+	ret = expires_dur + get_act_time();
+	LM_DBG("randomized expiry ts from %u to %lu (adj: %d/%d, "
+	       "max_deviation: %d)\n", expires_ts, ret, expires_adj,
+	       (int)ret - (int)expires_ts, expires_max_deviation);
+
+	return ret;
+}
+
 #endif /* __LIB_REG_COMMON_H__ */
diff --git a/lib/reg/doc/reg_modparams.xml b/lib/reg/doc/reg_modparams.xml
@@ -1,5 +1,39 @@
 <!-- Common registrar modparams-->
 
+	<section id="param_expires_max_deviation" xreflabel="expires_max_deviation">
+		<title><varname>expires_max_deviation</varname> (integer)</title>
+		<para>
+		Set this parameter in order to add a random +/- deviation up to
+		and including the given value to the expiration interval of a
+		newly registered contact.  For example, if this parameter is set to
+		<emphasis>100</emphasis> and a phone registers for 1800 sec, the final
+		expiry will be random number in the [1700, 1900] interval.
+		<para>
+		By randomizing the registration lifetimes of the contacts, the
+		server is better equipped to deal with a post-restart <emphasis>registration
+		storm</emphasis>, when all TCP connections are lost and a significant portion of
+		UAs will re-register at the same time.  Thanks to the contact lifetime
+		randomization, the registration storm will only happen once rather
+		than, e.g., every 1800 seconds following the restart.
+		</para>
+		</para>
+		<para>
+		<emphasis>
+			Default value is 0 (no deviation).
+		</emphasis>
+		</para>
+		<example>
+		<title>Setting the <varname>expires_max_deviation</varname> parameter</title>
+		<programlisting format="linespecific">
+...
+# add a random +/- 0-100 seconds to each registration lifetime
+modparam("&reg_module;", "expires_max_deviation", 100)
+...
+		</programlisting>
+		</example>
+	</section>
+
+
 	<section id="param_max_contacts" xreflabel="max_contacts">
 		<title><varname>max_contacts</varname> (integer)</title>
 		<para>

diff --git a/modules/mid_registrar/save.c b/modules/mid_registrar/save.c
@@ -1186,7 +1186,7 @@ struct ucontact_info *mid_reg_pack_ci(struct sip_msg *req, struct sip_msg *rpl,
 	ci.last_modified = get_act_time();
 	ci.flags = mri->ul_flags;
 	ci.cflags = mri->cflags;
-	ci.expires = ctmap->expires + get_act_time();
+	ci.expires = randomize_expires(ctmap->expires + get_act_time());
 	ci.shtag = mri->ownership_tag;
 
 	ci.q = ctmap->q;