diff --git a/src/builder/b-private.h b/src/builder/b-private.h
index 5b1ac65..c9bcff4 100644
--- a/src/builder/b-private.h
+++ b/src/builder/b-private.h
@@ -159,6 +159,9 @@ struct sai_builder {
 #endif
 	char			stay;
 
+	char			event_affinity[65];
+	char			event_affinity_active;
+
 	/* resource management */
 
 	uint64_t		ram_limit_kib;
diff --git a/src/builder/b-sai.c b/src/builder/b-sai.c
index e0daf92..4d656e5 100644
--- a/src/builder/b-sai.c
+++ b/src/builder/b-sai.c
@@ -528,6 +528,11 @@ saib_app_run(int argc, const char **argv)
 	if ((p = lws_cmdline_option(argc, argv, "-c")))
 		config_dir = p;
 
+	if (lws_cmdline_option(argc, argv, "-E")) {
+		builder.event_affinity_active = 1;
+		lwsl_notice("%s: event affinity mode enabled (ephemeral VM)\n", __func__);
+	}
+
 #if defined(__NetBSD__) || defined(__OpenBSD__)
 	if (lws_cmdline_option(argc, argv, "-D")) {
 		if (lws_daemonize("/var/run/sai_builder.pid"))
diff --git a/src/builder/b-task.c b/src/builder/b-task.c
index 453698b..2c9c006 100644
--- a/src/builder/b-task.c
+++ b/src/builder/b-task.c
@@ -177,6 +177,19 @@ saib_can_accept_task(sai_task_t *task, sai_plat_t *sp)
 
 	unsigned int executing = 0;
 
+	if (builder.event_affinity_active) {
+		if (!builder.event_affinity[0]) {
+			lws_strncpy(builder.event_affinity, task->event_uuid,
+				    sizeof(builder.event_affinity));
+			lwsl_notice("%s: locked affinity to event %s\n",
+				    __func__, builder.event_affinity);
+		} else if (strcmp(builder.event_affinity, task->event_uuid)) {
+			lwsl_notice("%s: reject task %s: affinity locked to %s\n",
+				    __func__, task->uuid, builder.event_affinity);
+			return 1;
+		}
+	}
+
 	if ((((builder.ram_limit_kib * 4) / 3) - builder.ram_reserved_kib) < task->est_peak_mem_kib) {
 		lwsl_notice("%s: reject task %s: not enough RAM: task %u vs %u lim - %u res\n", __func__,
 			    task->uuid, (unsigned int)task->est_peak_mem_kib, (unsigned int)builder.ram_limit_kib, (unsigned int)builder.ram_reserved_kib);