IMHO updated with https://issues.jboss.org/browse/MODCLUSTER-328

mod_proxy_cluster.c

/**
  * Find the best nodes for a request (check host and context (and balancer))
  * @param r the request_rec
  * @param balancer the balancer (balancer to use in that case we check it).
  * @param route from the sessionid if we have one.
  * @param use_alias compare alias with server_name
  * @return a pointer to a list of nodes.
  */
 static node_context *find_node_context_host(request_rec *r, proxy_balancer *balancer, const char *route, int use_alias, proxy_vhost_table* vhost_table, proxy_context_table* context_table)
 {
     int sizecontext = context_table->sizecontext;
     int *contexts;
     int *length;
     int *status;
     int i, j, max;
     node_context *best;
     int nbest;
     const char *uri = NULL;
+    const char *luri = NULL;
 
     /* use r->uri (trans) or r->filename (after canon or rewrite) */
     if (r->filename) {
         const char *scheme = strstr(r->filename, "://");
         if (scheme)
-            uri = ap_strchr_c(scheme + 3, '/');
+            luri = ap_strchr_c(scheme + 3, '/');
     }
-    if (!uri)
+    if (!luri)
+       luri = r->uri;
+    uri = ap_strchr_c(luri, '?');
+    if (uri)
+       uri = apr_pstrndup(r->pool, luri, uri - luri);
+    else
        uri = r->uri;
 
     /* read the contexts */
     if (sizecontext == 0)
         return NULL;
     contexts =  apr_palloc(r->pool, sizeof(int)*sizecontext);
     for (i=0; i < sizecontext; i++)
         contexts[i] = i;
     length =  apr_pcalloc(r->pool, sizeof(int)*sizecontext);
     status =  apr_palloc(r->pool, sizeof(int)*sizecontext);
     /* Check the virtual host */
     if (use_alias) {
         /* read the hosts */
         int sizevhost;
         int *contextsok = apr_pcalloc(r->pool, sizeof(int)*sizecontext);
         const char *hostname = ap_get_server_name(r);
 #if HAVE_CLUSTER_EX_DEBUG
     ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                      "find_node_context_host: Host: %s", hostname);
 #endif
         sizevhost = vhost_table->sizevhost;
         for (i=0; i<sizevhost; i++) {
             hostinfo_t *vhost = vhost_table->vhost_info + i;
             if (strcmp(hostname, vhost->host) == 0) {
                 /* add the contexts that match */
                 for (j=0; j<sizecontext; j++) {
                     contextinfo_t *context = &context_table->context_info[j];
                     if (context->vhost == vhost->vhost && context->node == vhost->node)
                         contextsok[j] = 1;
                 }
             }
         }
         for (j=0; j<sizecontext; j++) {
             if (!contextsok[j])
                 contexts[j] = -1;
         }
     }
 #if HAVE_CLUSTER_EX_DEBUG
     for (j=0; j<sizecontext; j++) {
         contextinfo_t *context;
         if (contexts[j] == -1) continue;
         context = &context_table->context_info[j]; 
         ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
-                         "find_node_context_host: node: %d vhost: %d context: %s",
-                          context->node, context->vhost, context->context);
+                         "find_node_context_host: %s node: %d vhost: %d context: %s",
+                          uri, context->node, context->vhost, context->context);
     }
 #endif
 
     /* Check the contexts */
     max = 0;
     for (j=0; j<sizecontext; j++) {
         contextinfo_t *context;
         int len;
         if (contexts[j] == -1) continue;
         context = &context_table->context_info[j];
 
         /* keep only the contexts corresponding to our balancer */
         if (balancer != NULL) {
             nodeinfo_t *node;
             if (node_storage->read_node(context->node, &node) != APR_SUCCESS)
                 continue;
 #if AP_MODULE_MAGIC_AT_LEAST(20101223,1)
             if (strlen(balancer->s->name) > 11 && strcasecmp(&balancer->s->name[11], node->mess.balancer) != 0)
 #else
             if (strlen(balancer->name) > 11 && strcasecmp(&balancer->name[11], node->mess.balancer) != 0)
 #endif
                 continue;
         }
         len = strlen(context->context);
         if (strncmp(uri, context->context, len) == 0) {
             if (uri[len] == '\0' || uri[len] == '/' || len==1) {
                 status[j] = context->status;
                 length[j] = len;
                 if (len > max) {
                     max = len;
                 } 
             }
         }
     }
     if (max == 0)
         return NULL;
 
 
     /* find the best matching contexts */
     nbest = 1;
     for (j=0; j<sizecontext; j++)
         if (length[j] == max)
             nbest++;
     best =  apr_palloc(r->pool, sizeof(node_context)*nbest);
     nbest  = 0;
     for (j=0; j<sizecontext; j++)
         if (length[j] == max) {
             contextinfo_t *context;
             int ok = 0;
             context = &context_table->context_info[j];
             /* Check status */
             switch (status[j]) {
                 case ENABLED:
                     ok = -1;
                     break;
                 case DISABLED:
                     /* Only the request with sessionid ok for it */
                     if (hassession_byname(r, context->node, route)) {
                         ok = -1;
                     }
                     break;
             }
             if (ok) {
                 best[nbest].node = context->node;
                 best[nbest].context = context->id;
                 nbest++;
             }
         }
     if (nbest == 0)
         return NULL;
     best[nbest].node = -1;
     return best; 
 }

Fix:

• uri = r->uri;
• uri = luri;

https://issues.jboss.org/browse/MODCLUSTER-335