MEDIUM: backend: add new "balance hash <expr>" algorithm
Almost all of our hash-based LB algorithms are implemented as special
cases of something that can now be achieved using sample expressions,
and some of them have adopted some options to adapt their behavior in
ways that could also be achieved using converters.
There are users who want to hash other parameters that are combined
into variables, and who set headers from these values and use
"balance hdr(name)" for this.
Instead of constantly implementing specific options and having users
hack around when they want a real hash, let's implement a native hash
mode that applies to a standard sample expression. This way, any
fetchable element (including variables) may be used to construct the
hash, even modified by any converter if desired.
diff --git a/src/backend.c b/src/backend.c
index 18c84f4..c4a0868 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -524,6 +524,40 @@
return map_get_server_hash(px, hash);
}
+/* sample expression HASH. Returns NULL if the sample is not found or if there
+ * are no server, relying on the caller to fall back to round robin instead.
+ */
+static struct server *get_server_expr(struct stream *s, const struct server *avoid)
+{
+ struct proxy *px = s->be;
+ struct sample *smp;
+ unsigned int hash = 0;
+
+ if (px->lbprm.tot_weight == 0)
+ return NULL;
+
+ /* note: no need to hash if there's only one server left */
+ if (px->lbprm.tot_used == 1)
+ goto hash_done;
+
+ smp = sample_fetch_as_type(px, s->sess, s, SMP_OPT_DIR_REQ | SMP_OPT_FINAL, px->lbprm.expr, SMP_T_BIN);
+ if (!smp)
+ return NULL;
+
+ /* We have the desired data. Let's hash it according to the configured
+ * options and algorithm.
+ */
+ hash = gen_hash(px, smp->data.u.str.area, smp->data.u.str.data);
+
+ if ((px->lbprm.algo & BE_LB_HASH_MOD) == BE_LB_HMOD_AVAL)
+ hash = full_hash(hash);
+ hash_done:
+ if ((px->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
+ return chash_get_server_hash(px, hash, avoid);
+ else
+ return map_get_server_hash(px, hash);
+}
+
/* random value */
static struct server *get_server_rnd(struct stream *s, const struct server *avoid)
{
@@ -760,6 +794,11 @@
srv = get_server_rch(s, prev_srv);
break;
+ case BE_LB_HASH_SMP:
+ /* sample expression hashing */
+ srv = get_server_expr(s, prev_srv);
+ break;
+
default:
/* unknown balancing algorithm */
err = SRV_STATUS_INTERNAL;
@@ -2578,6 +2617,8 @@
return "hdr";
else if (algo == BE_LB_ALGO_RCH)
return "rdp-cookie";
+ else if (algo == BE_LB_ALGO_SMP)
+ return "hash";
else if (algo == BE_LB_ALGO_NONE)
return "none";
else
@@ -2707,6 +2748,23 @@
}
}
}
+ else if (strcmp(args[0], "hash") == 0) {
+ if (!*args[1]) {
+ memprintf(err, "%s requires a sample expression.", args[0]);
+ return -1;
+ }
+ curproxy->lbprm.algo &= ~BE_LB_ALGO;
+ curproxy->lbprm.algo |= BE_LB_ALGO_SMP;
+
+ ha_free(&curproxy->lbprm.arg_str);
+ curproxy->lbprm.arg_str = strdup(args[1]);
+ curproxy->lbprm.arg_len = strlen(args[1]);
+
+ if (*args[2]) {
+ memprintf(err, "%s takes no other argument (got '%s').", args[0], args[2]);
+ return -1;
+ }
+ }
else if (!strncmp(args[0], "hdr(", 4)) {
const char *beg, *end;