Static load balancer

Hello,

please consider the following situation:
I have a dynamic web application (served by lighty over fast_cgi or
reverse proxy) which is distributed over 2 hosts (IP A and B). The
selection between them is done by round robin dns. It is done for
reliability reasons (not performance problems).

When deploying a new version I need to reastart the fast_cgi process (or
application web server). In this time there would be an error (502 bad
gateway in case of the proxy). So I would like to set up this:

Host A:
$HTTP["url"] =~ "^/" {
    proxy-core.protocol = "http"
    proxy-core.balancer = "static"
    proxy-core.backends = (
        "A:3000",
        "B:3000",
    )
    proxy-core.max-pool-size = 16
}

Host B:
$HTTP["url"] =~ "^/" {
    proxy-core.protocol = "http"
    proxy-core.balancer = "static"
    proxy-core.backends = (
        "B:3000",
        "A:3000",
    )
    proxy-core.max-pool-size = 16
}

So it sould only jump to the "other" (remote) host, when the local host
is not available (due to a restart or whatever).

Can this behaviour achieved with the existing load balancers? I thought
not, and wrote a very simple static load balancer (feel free to rename
it). It works as expected.

Does this make sense? Can this (or some other solution) please be
included in lighty?

Thanks, a lot.
Bye, Uwe

Index: src/mod_proxy_core_backend.h
===================================================================
--- src/mod_proxy_core_backend.h	(Revision 1537)
+++ src/mod_proxy_core_backend.h	(Arbeitskopie)
@@ -28,7 +28,8 @@
 	PROXY_BALANCE_UNSET,
 	PROXY_BALANCE_SQF,
 	PROXY_BALANCE_CARP,
-	PROXY_BALANCE_RR
+	PROXY_BALANCE_RR,
+	PROXY_BALANCE_STATIC
 } proxy_balance_t;

 typedef struct {
Index: src/mod_proxy_core.c
===================================================================
--- src/mod_proxy_core.c	(Revision 1537)
+++ src/mod_proxy_core.c	(Arbeitskopie)
@@ -73,6 +73,7 @@
 	array_insert_int(p->possible_balancers, "sqf", PROXY_BALANCE_SQF);
 	array_insert_int(p->possible_balancers, "carp", PROXY_BALANCE_CARP);
 	array_insert_int(p->possible_balancers, "round-robin", PROXY_BALANCE_RR);
+	array_insert_int(p->possible_balancers, "static", PROXY_BALANCE_STATIC);

 	p->proxy_register_protocol = mod_proxy_core_register_protocol;

@@ -1483,6 +1484,19 @@
 		}

 		break;
+	case PROXY_BALANCE_STATIC:
+		/* static (only fail-over) */
+
+		for (i = 0; i < address_pool->used; i++) {
+			cur_address = address_pool->ptr[i];
+
+			if (cur_address->state != PROXY_ADDRESS_STATE_ACTIVE) continue;
+
+			address = cur_address;
+			break;
+		}
+
+		break;
 	case PROXY_BALANCE_SQF:
 		/* shortest-queue-first balancing */