Hi,
In the interests of load-balancing and redundancy, we found it would be
helpful if there was more control over how the list of spamd servers in
spamd_addresses is used. The attached patch adds an MX-style priority as
an optional third argument to each ip/port combination, so that it is
possible to offload spam checking to a server or group of servers. and
fall back onto another server should none of these be contactable.
The general idea is that as spam processing becomes a greater drain on
system resources, it becomes practical to offload this burden onto a
dedicated machine (which can then become a cluster of machines once the
load becomes too high). This leaves the MX server free to concentrate on
mail delivery and processing ACL checks. However in the event of a
failure of the offload server, it would be useful to be able to fall
back onto a backup running elsewhere, for example on localhost.
This patch preserves the usual spamd_address behaviour at each level of
priority; the default priority for a server is 10 and a random(ish)
server will be chosen to begin with, then the list cycles in order.
I have tested it a little to ensure the functionality is correct, and
would be interested in any feedback and comments on the idea. The patch
is against the 4.63 source tree.
Cheers,
--alex
diff -ur exim-4.63/src/spam.c exim-4.63-spam-mx/src/spam.c
--- exim-4.63/src/spam.c Mon Jul 31 15:19:48 2006
+++ exim-4.63-spam-mx/src/spam.c Tue Aug 22 16:46:08 2006
@@ -20,6 +20,18 @@
uschar prev_user_name[128] = "";
int spam_ok = 0;
int spam_rc = 0;
+int rand_server = 0;
+int num_servers = 0;
+
+int sort_by_prio(const void *ia, const void *ib) {
+ spamd_address_container * const *a = ia;
+ const spamd_address_container * const *b = ib;
+ if ((*a)->priority - (*b)->priority)
+ return (*a)->priority - (*b)->priority;
+ /* pseudo-randomisation of equal priorities
+ * will only change once per second, as before */
+ return ((*a)->pos + rand_server)%num_servers - ((*b)->pos +
rand_server)%num_servers;
+}
int spam(uschar **listptr) {
int sep = 0;
@@ -92,14 +104,14 @@
/* socket does not start with '/' -> network socket */
if (*spamd_address != '/') {
time_t now = time(NULL);
- int num_servers = 0;
int current_server = 0;
- int start_server = 0;
uschar *address = NULL;
uschar *spamd_address_list_ptr = spamd_address;
uschar address_buffer[256];
spamd_address_container * spamd_address_vector[32];
+ num_servers = 0;
+
/* Check how many spamd servers we have
and register their addresses */
while ((address = string_nextinlist(&spamd_address_list_ptr, &sep,
@@ -108,9 +120,17 @@
spamd_address_container *this_spamd =
(spamd_address_container *)store_get(sizeof(spamd_address_container));
+
+ /* set a default spamd priority of 10 */
+ this_spamd->priority = 10;
+ /* store current server number for randomisation purposes */
+ this_spamd->pos = num_servers;
/* grok spamd address and port */
- if( sscanf(CS address, "%s %u", this_spamd->tcp_addr,
&(this_spamd->tcp_port)) != 2 ) {
+ if( sscanf(CS address, "%s %u %i",
+ this_spamd->tcp_addr,
+ &(this_spamd->tcp_port),
+ &(this_spamd->priority)) < 2 ) {
log_write(0, LOG_MAIN,
"spam acl condition: warning - invalid spamd address: '%s'",
address);
continue;
@@ -130,13 +150,15 @@
return DEFER;
};
- current_server = start_server = (int)now % num_servers;
+ rand_server = (int)now % num_servers;
+ qsort(spamd_address_vector, num_servers, sizeof(*spamd_address_vector),
sort_by_prio);
while (1) {
- debug_printf("trying server %s, port %u\n",
+ debug_printf("trying server %s, port %u, priority %d\n",
spamd_address_vector[current_server]->tcp_addr,
- spamd_address_vector[current_server]->tcp_port);
+ spamd_address_vector[current_server]->tcp_port,
+ spamd_address_vector[current_server]->priority);
/* contact a spamd */
if ( (spamd_sock = ip_socket(SOCK_STREAM, AF_INET)) < 0) {
@@ -161,9 +183,7 @@
spamd_address_vector[current_server]->tcp_port,
strerror(errno));
current_server++;
- if (current_server >= num_servers)
- current_server = 0;
- if (current_server == start_server) {
+ if (current_server == num_servers) {
log_write(0, LOG_MAIN|LOG_PANIC, "spam acl condition: all spamd
servers failed");
(void)fclose(mbox_file);
(void)close(spamd_sock);
diff -ur exim-4.63/src/spam.h exim-4.63-spam-mx/src/spam.h
--- exim-4.63/src/spam.h Mon Jul 31 15:19:48 2006
+++ exim-4.63-spam-mx/src/spam.h Tue Aug 22 13:35:20 2006
@@ -25,6 +25,8 @@
typedef struct spamd_address_container {
uschar tcp_addr[24];
unsigned int tcp_port;
+ int priority;
+ int pos;
} spamd_address_container;
#endif
--
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