Expand SB.Template_Var records in two stages:
1. first expand them to local values in match/action strings
2. then reparse the expanded strings

For the case when a lflow references a Template_Var also track
references (similar to the ones maintained for multicast groups, address
sets, port_groups, port bindings).

Signed-off-by: Dumitru Ceara <[email protected]>
---
 controller/lflow.c          |   59 +++++++-
 controller/lflow.h          |    1 
 controller/lport.c          |    3 
 controller/ofctrl.c         |    9 +
 controller/ofctrl.h         |    3 
 controller/ovn-controller.c |  317 +++++++++++++++++++++++++++++++++++++++++++
 include/ovn/expr.h          |    4 -
 include/ovn/lex.h           |   14 +-
 lib/actions.c               |    9 +
 lib/expr.c                  |   18 ++
 lib/lex.c                   |   55 +++++++
 lib/objdep.c                |    1 
 lib/objdep.h                |    1 
 lib/ovn-util.c              |    7 +
 lib/ovn-util.h              |    3 
 tests/ovn.at                |    2 
 tests/test-ovn.c            |   16 ++
 utilities/ovn-trace.c       |   26 +++-
 18 files changed, 512 insertions(+), 36 deletions(-)

diff --git a/controller/lflow.c b/controller/lflow.c
index f9f2e6286..ad58fcd3c 100644
--- a/controller/lflow.c
+++ b/controller/lflow.c
@@ -81,6 +81,8 @@ convert_match_to_expr(const struct sbrec_logical_flow *,
                       const struct local_datapath *ldp,
                       struct expr **prereqs, const struct shash *addr_sets,
                       const struct shash *port_groups,
+                      const struct smap *template_vars,
+                      struct sset *template_vars_ref,
                       struct objdep_mgr *, bool *pg_addr_set_ref);
 static void
 add_matches_to_flow_table(const struct sbrec_logical_flow *,
@@ -356,10 +358,15 @@ consider_lflow_for_added_as_ips__(
         .n_tables = LOG_PIPELINE_LEN,
         .cur_ltable = lflow->table_id,
     };
+    struct sset template_vars_ref = SSET_INITIALIZER(&template_vars_ref);
     struct expr *prereqs = NULL;
     char *error;
 
-    error = ovnacts_parse_string(lflow->actions, &pp, &ovnacts, &prereqs);
+    char *actions_s = lexer_parse_template_string(xstrdup(lflow->actions),
+                                                  l_ctx_in->template_vars,
+                                                  &template_vars_ref);
+    error = ovnacts_parse_string(actions_s, &pp, &ovnacts, &prereqs);
+    free(actions_s);
     if (error) {
         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
         VLOG_WARN_RL(&rl, "error parsing actions \"%s\": %s",
@@ -367,6 +374,7 @@ consider_lflow_for_added_as_ips__(
         free(error);
         ovnacts_free(ovnacts.data, ovnacts.size);
         ofpbuf_uninit(&ovnacts);
+        sset_destroy(&template_vars_ref);
         return true;
     }
 
@@ -430,6 +438,8 @@ consider_lflow_for_added_as_ips__(
     struct expr *expr = convert_match_to_expr(lflow, ldp, &prereqs,
                                               l_ctx_in->addr_sets,
                                               l_ctx_in->port_groups,
+                                              l_ctx_in->template_vars,
+                                              &template_vars_ref,
                                               l_ctx_out->lflow_deps_mgr, NULL);
     shash_replace((struct shash *)l_ctx_in->addr_sets, as_name, real_as);
     if (new_fake_as) {
@@ -501,6 +511,14 @@ done:
     ofpbuf_uninit(&ovnacts);
     expr_destroy(expr);
     expr_matches_destroy(&matches);
+
+    const char *tv_name;
+    SSET_FOR_EACH (tv_name, &template_vars_ref) {
+        objdep_mgr_add(l_ctx_out->lflow_deps_mgr, OBJDEP_TYPE_TEMPLATE,
+                       tv_name, &lflow->header_.uuid);
+    }
+    sset_destroy(&template_vars_ref);
+
     return handled;
 }
 
@@ -911,6 +929,8 @@ convert_match_to_expr(const struct sbrec_logical_flow 
*lflow,
                       struct expr **prereqs,
                       const struct shash *addr_sets,
                       const struct shash *port_groups,
+                      const struct smap *template_vars,
+                      struct sset *template_vars_ref,
                       struct objdep_mgr *mgr,
                       bool *pg_addr_set_ref)
 {
@@ -918,11 +938,16 @@ convert_match_to_expr(const struct sbrec_logical_flow 
*lflow,
     struct sset port_groups_ref = SSET_INITIALIZER(&port_groups_ref);
     char *error = NULL;
 
-    struct expr *e = expr_parse_string(lflow->match, &symtab, addr_sets,
+    char *match_s = lexer_parse_template_string(xstrdup(lflow->match),
+                                                template_vars,
+                                                template_vars_ref);
+    struct expr *e = expr_parse_string(match_s, &symtab, addr_sets,
                                        port_groups, &addr_sets_ref,
                                        &port_groups_ref,
                                        ldp->datapath->tunnel_key,
                                        &error);
+    free(match_s);
+
     struct shash_node *addr_sets_ref_node;
     SHASH_FOR_EACH (addr_sets_ref_node, &addr_sets_ref) {
         objdep_mgr_add_with_refcount(mgr, OBJDEP_TYPE_ADDRSET,
@@ -1027,7 +1052,12 @@ consider_logical_flow__(const struct sbrec_logical_flow 
*lflow,
     struct expr *prereqs = NULL;
     char *error;
 
-    error = ovnacts_parse_string(lflow->actions, &pp, &ovnacts, &prereqs);
+    struct sset template_vars_ref = SSET_INITIALIZER(&template_vars_ref);
+    char *actions_s = lexer_parse_template_string(xstrdup(lflow->actions),
+                                                  l_ctx_in->template_vars,
+                                                  &template_vars_ref);
+    error = ovnacts_parse_string(actions_s, &pp, &ovnacts, &prereqs);
+    free(actions_s);
     if (error) {
         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
         VLOG_WARN_RL(&rl, "error parsing actions \"%s\": %s",
@@ -1035,6 +1065,7 @@ consider_logical_flow__(const struct sbrec_logical_flow 
*lflow,
         free(error);
         ovnacts_free(ovnacts.data, ovnacts.size);
         ofpbuf_uninit(&ovnacts);
+        sset_destroy(&template_vars_ref);
         return;
     }
 
@@ -1085,6 +1116,8 @@ consider_logical_flow__(const struct sbrec_logical_flow 
*lflow,
     case LCACHE_T_NONE:
         expr = convert_match_to_expr(lflow, ldp, &prereqs, l_ctx_in->addr_sets,
                                      l_ctx_in->port_groups,
+                                     l_ctx_in->template_vars,
+                                     &template_vars_ref,
                                      l_ctx_out->lflow_deps_mgr,
                                      &pg_addr_set_ref);
         if (!expr) {
@@ -1099,11 +1132,13 @@ consider_logical_flow__(const struct sbrec_logical_flow 
*lflow,
     }
 
     /* If caching is enabled and this is a not cached expr that doesn't refer
-     * to address sets or port groups, save it to potentially cache it later.
+     * to address sets, port groups, or template variables, save it to
+     * potentially cache it later.
      */
     if (lcv_type == LCACHE_T_NONE
             && lflow_cache_is_enabled(l_ctx_out->lflow_cache)
-            && !pg_addr_set_ref) {
+            && !pg_addr_set_ref
+            && sset_is_empty(&template_vars_ref)) {
         cached_expr = expr_clone(expr);
     }
 
@@ -1188,6 +1223,13 @@ done:
     expr_destroy(cached_expr);
     expr_matches_destroy(matches);
     free(matches);
+
+    const char *tv_name;
+    SSET_FOR_EACH (tv_name, &template_vars_ref) {
+        objdep_mgr_add(l_ctx_out->lflow_deps_mgr, OBJDEP_TYPE_TEMPLATE,
+                       tv_name, &lflow->header_.uuid);
+    }
+    sset_destroy(&template_vars_ref);
 }
 
 static void
@@ -1951,8 +1993,7 @@ add_lb_ct_snat_hairpin_flows(struct ovn_controller_lb *lb,
 
 static void
 consider_lb_hairpin_flows(const struct sbrec_load_balancer *sbrec_lb,
-                          const struct hmap *local_datapaths,
-                          bool use_ct_mark,
+                          const struct hmap *local_datapaths, bool use_ct_mark,
                           struct ovn_desired_flow_table *flow_table,
                           struct simap *ids)
 {
@@ -2041,8 +2082,8 @@ add_lb_hairpin_flows(const struct 
sbrec_load_balancer_table *lb_table,
             ovs_assert(id_pool_alloc_id(pool, &id));
             simap_put(ids, lb->name, id);
         }
-        consider_lb_hairpin_flows(lb, local_datapaths, use_ct_mark,
-                                  flow_table, ids);
+        consider_lb_hairpin_flows(lb, local_datapaths, use_ct_mark, flow_table,
+                                  ids);
     }
 }
 
diff --git a/controller/lflow.h b/controller/lflow.h
index a9a0f7506..8175bdbea 100644
--- a/controller/lflow.h
+++ b/controller/lflow.h
@@ -112,6 +112,7 @@ struct lflow_ctx_in {
     const struct hmap *dhcp_opts;
     const struct hmap *dhcpv6_opts;
     const struct controller_event_options *controller_event_opts;
+    const struct smap *template_vars;
     bool lb_hairpin_use_ct_mark;
 };
 
diff --git a/controller/lport.c b/controller/lport.c
index add7e91aa..f12ce4e63 100644
--- a/controller/lport.c
+++ b/controller/lport.c
@@ -134,8 +134,7 @@ lport_can_bind_on_this_chassis(const struct sbrec_chassis 
*chassis_rec,
     enum can_bind can_bind = CAN_BIND_AS_MAIN;
     for (chassis = strtok_r(tokstr, ",", &save_ptr); chassis != NULL;
          chassis = strtok_r(NULL, ",", &save_ptr)) {
-        if (!strcmp(chassis, chassis_rec->name)
-                || !strcmp(chassis, chassis_rec->hostname)) {
+        if (chassis_name_equals(chassis, chassis_rec)) {
             free(tokstr);
             return can_bind;
         }
diff --git a/controller/ofctrl.c b/controller/ofctrl.c
index c77991258..bf161dfde 100644
--- a/controller/ofctrl.c
+++ b/controller/ofctrl.c
@@ -2873,7 +2873,8 @@ ofctrl_lookup_port(const void *br_int_, const char 
*port_name,
 char *
 ofctrl_inject_pkt(const struct ovsrec_bridge *br_int, const char *flow_s,
                   const struct shash *addr_sets,
-                  const struct shash *port_groups)
+                  const struct shash *port_groups,
+                  const struct smap *template_vars)
 {
     int version = rconn_get_version(swconn);
     if (version < 0) {
@@ -2881,9 +2882,13 @@ ofctrl_inject_pkt(const struct ovsrec_bridge *br_int, 
const char *flow_s,
     }
 
     struct flow uflow;
-    char *error = expr_parse_microflow(flow_s, &symtab, addr_sets,
+    char *flow_exp_s = lexer_parse_template_string(xstrdup(flow_s),
+                                                   template_vars,
+                                                   NULL);
+    char *error = expr_parse_microflow(flow_exp_s, &symtab, addr_sets,
                                        port_groups, ofctrl_lookup_port,
                                        br_int, &uflow);
+    free(flow_exp_s);
     if (error) {
         return error;
     }
diff --git a/controller/ofctrl.h b/controller/ofctrl.h
index 71d3f5838..396824512 100644
--- a/controller/ofctrl.h
+++ b/controller/ofctrl.h
@@ -71,7 +71,8 @@ void ofctrl_ct_flush_zone(uint16_t zone_id);
 
 char *ofctrl_inject_pkt(const struct ovsrec_bridge *br_int,
                         const char *flow_s, const struct shash *addr_sets,
-                        const struct shash *port_groups);
+                        const struct shash *port_groups,
+                        const struct smap *template_vars);
 
 /* Flow table interfaces to the rest of ovn-controller. */
 
diff --git a/controller/ovn-controller.c b/controller/ovn-controller.c
index 32a24a076..40afebf4e 100644
--- a/controller/ovn-controller.c
+++ b/controller/ovn-controller.c
@@ -91,6 +91,7 @@ static unixctl_cb_func debug_pause_execution;
 static unixctl_cb_func debug_resume_execution;
 static unixctl_cb_func debug_status_execution;
 static unixctl_cb_func debug_dump_local_bindings;
+static unixctl_cb_func debug_dump_local_template_vars;
 static unixctl_cb_func debug_dump_lflow_conj_ids;
 static unixctl_cb_func lflow_cache_flush_cmd;
 static unixctl_cb_func lflow_cache_show_stats_cmd;
@@ -170,6 +171,8 @@ update_sb_monitors(struct ovsdb_idl *ovnsb_idl,
      *
      * Monitor IGMP_Groups for local chassis.
      *
+     * Monitor Template_Var for local chassis.
+     *
      * We always monitor patch ports because they allow us to see the linkages
      * between related logical datapaths.  That way, when we know that we have
      * a VIF on a particular logical switch, we immediately know to monitor all
@@ -184,6 +187,7 @@ update_sb_monitors(struct ovsdb_idl *ovnsb_idl,
     struct ovsdb_idl_condition ip_mcast = OVSDB_IDL_CONDITION_INIT(&ip_mcast);
     struct ovsdb_idl_condition igmp = OVSDB_IDL_CONDITION_INIT(&igmp);
     struct ovsdb_idl_condition chprv = OVSDB_IDL_CONDITION_INIT(&chprv);
+    struct ovsdb_idl_condition tv = OVSDB_IDL_CONDITION_INIT(&tv);
 
     /* Always monitor all logical datapath groups. Otherwise, DPG updates may
      * be received *after* the lflows using it are seen by ovn-controller.
@@ -201,6 +205,7 @@ update_sb_monitors(struct ovsdb_idl *ovnsb_idl,
         ovsdb_idl_condition_add_clause_true(&ip_mcast);
         ovsdb_idl_condition_add_clause_true(&igmp);
         ovsdb_idl_condition_add_clause_true(&chprv);
+        ovsdb_idl_condition_add_clause_true(&tv);
         goto out;
     }
 
@@ -239,6 +244,11 @@ update_sb_monitors(struct ovsdb_idl *ovnsb_idl,
         /* Monitors Chassis_Private record for current chassis only. */
         sbrec_chassis_private_add_clause_name(&chprv, OVSDB_F_EQ,
                                               chassis->name);
+
+        sbrec_template_var_add_clause_chassis_name(&tv, OVSDB_F_EQ,
+                                                   chassis->name);
+        sbrec_template_var_add_clause_chassis_name(&tv, OVSDB_F_EQ,
+                                                   chassis->hostname);
     } else {
         /* During initialization, we monitor all records in Chassis_Private so
          * that we don't try to recreate existing ones. */
@@ -290,6 +300,7 @@ out:;
         sbrec_ip_multicast_set_condition(ovnsb_idl, &ip_mcast),
         sbrec_igmp_group_set_condition(ovnsb_idl, &igmp),
         sbrec_chassis_private_set_condition(ovnsb_idl, &chprv),
+        sbrec_template_var_set_condition(ovnsb_idl, &tv),
     };
 
     unsigned int expected_cond_seqno = 0;
@@ -307,6 +318,7 @@ out:;
     ovsdb_idl_condition_destroy(&ip_mcast);
     ovsdb_idl_condition_destroy(&igmp);
     ovsdb_idl_condition_destroy(&chprv);
+    ovsdb_idl_condition_destroy(&tv);
     return expected_cond_seqno;
 }
 
@@ -990,7 +1002,8 @@ ctrl_register_ovs_idl(struct ovsdb_idl *ovs_idl)
     SB_NODE(load_balancer, "load_balancer") \
     SB_NODE(fdb, "fdb") \
     SB_NODE(meter, "meter") \
-    SB_NODE(static_mac_binding, "static_mac_binding")
+    SB_NODE(static_mac_binding, "static_mac_binding") \
+    SB_NODE(template_var, "template_var")
 
 enum sb_engine_node {
 #define SB_NODE(NAME, NAME_STR) SB_##NAME,
@@ -1652,6 +1665,214 @@ runtime_data_sb_datapath_binding_handler(struct 
engine_node *node OVS_UNUSED,
     return true;
 }
 
+struct local_templates {
+    struct uuidset uuids;
+    struct smap vars;
+};
+
+static void
+local_templates_init(struct local_templates *table)
+{
+    uuidset_init(&table->uuids);
+    smap_init(&table->vars);
+}
+
+static void
+local_templates_clear(struct local_templates *table)
+{
+    uuidset_clear(&table->uuids);
+    smap_clear(&table->vars);
+}
+
+static void
+local_templates_destroy(struct local_templates *table)
+{
+    uuidset_destroy(&table->uuids);
+    smap_destroy(&table->vars);
+}
+
+static void
+local_templates_insert(struct local_templates *table,
+                       const char *name, const struct uuid *uuid,
+                       const char *value)
+{
+    uuidset_insert(&table->uuids, uuid);
+    smap_replace(&table->vars, name, value);
+}
+
+static void
+local_templates_remove(struct local_templates *table,
+                       const char *name, const struct uuid *uuid)
+{
+    uuidset_find_and_delete(&table->uuids, uuid);
+    smap_remove(&table->vars, name);
+}
+
+static bool
+local_templates_contains_uuid(const struct local_templates *table,
+                              const struct uuid *uuid)
+{
+    return !!uuidset_find(CONST_CAST(struct uuidset *, &table->uuids), uuid);
+}
+
+static void
+local_templates_to_string(const struct local_templates *table,
+                             struct ds *out_data)
+{
+    const struct smap_node *node;
+
+    SMAP_FOR_EACH (node, &table->vars) {
+        ds_put_format(out_data, "name: '%s' value: '%s'\n",
+                      node->key, node->value);
+    }
+}
+
+struct ed_type_template_vars {
+    struct local_templates var_table;
+
+    bool change_tracked;
+    struct sset new;
+    struct sset deleted;
+    struct sset updated;
+};
+
+static void
+template_vars_init(const struct sbrec_template_var_table *tv_table,
+                   const struct sbrec_chassis *chassis,
+                   struct local_templates *var_table)
+{
+    const struct sbrec_template_var *tv;
+    SBREC_TEMPLATE_VAR_TABLE_FOR_EACH (tv, tv_table) {
+        if (chassis_name_equals(tv->chassis_name, chassis)) {
+            local_templates_insert(var_table, tv->name,
+                                      &tv->header_.uuid, tv->value);
+        }
+    }
+}
+
+static void
+template_vars_update(const struct sbrec_template_var_table *tv_table,
+                     const struct sbrec_chassis *chassis,
+                     struct local_templates *var_table,
+                     struct sset *new, struct sset *deleted,
+                     struct sset *updated)
+{
+    const struct sbrec_template_var *tv;
+    SBREC_TEMPLATE_VAR_TABLE_FOR_EACH_TRACKED (tv, tv_table) {
+        if (!sbrec_template_var_is_deleted(tv)) {
+            continue;
+        }
+
+        if (!local_templates_contains_uuid(var_table, &tv->header_.uuid)) {
+            continue;
+        }
+
+        local_templates_remove(var_table, tv->name, &tv->header_.uuid);
+        sset_add(deleted, tv->name);
+    }
+
+    SBREC_TEMPLATE_VAR_TABLE_FOR_EACH_TRACKED (tv, tv_table) {
+        if (sbrec_template_var_is_deleted(tv)) {
+            continue;
+        }
+
+        struct sset *tv_set = sbrec_template_var_is_new(tv)
+                              ? new : updated;
+        if (chassis_name_equals(tv->chassis_name, chassis)) {
+            local_templates_insert(var_table, tv->name,
+                                      &tv->header_.uuid, tv->value);
+            sset_add(tv_set, tv->name);
+        }
+    }
+}
+
+static void *
+en_template_vars_init(struct engine_node *node OVS_UNUSED,
+                      struct engine_arg *arg OVS_UNUSED)
+{
+    struct ed_type_template_vars *tv_data = xzalloc(sizeof *tv_data);
+    local_templates_init(&tv_data->var_table);
+    tv_data->change_tracked = false;
+    sset_init(&tv_data->new);
+    sset_init(&tv_data->deleted);
+    sset_init(&tv_data->updated);
+    return tv_data;
+}
+
+static void
+en_template_vars_run(struct engine_node *node, void *data)
+{
+    struct ed_type_template_vars *tv_data = data;
+
+    const struct sbrec_template_var_table *tv_table =
+        EN_OVSDB_GET(engine_get_input("SB_template_var", node));
+    const struct ovsrec_open_vswitch_table *ovs_table =
+        EN_OVSDB_GET(engine_get_input("OVS_open_vswitch", node));
+    struct ovsdb_idl_index *sbrec_chassis_by_name =
+        engine_ovsdb_node_get_index(engine_get_input("SB_chassis", node),
+                                    "name");
+    const struct sbrec_chassis *chassis =
+        chassis_lookup_by_name(sbrec_chassis_by_name,
+                               get_ovs_chassis_id(ovs_table));
+
+    local_templates_clear(&tv_data->var_table);
+
+    template_vars_init(tv_table, chassis, &tv_data->var_table);
+    engine_set_node_state(node, EN_UPDATED);
+}
+
+static bool
+template_vars_sb_template_var_handler(struct engine_node *node, void *data)
+{
+    struct ed_type_template_vars *tv_data = data;
+
+    const struct sbrec_template_var_table *tv_table =
+        EN_OVSDB_GET(engine_get_input("SB_template_var", node));
+    const struct ovsrec_open_vswitch_table *ovs_table =
+        EN_OVSDB_GET(engine_get_input("OVS_open_vswitch", node));
+    struct ovsdb_idl_index *sbrec_chassis_by_name =
+        engine_ovsdb_node_get_index(engine_get_input("SB_chassis", node),
+                                    "name");
+    const struct sbrec_chassis *chassis =
+        chassis_lookup_by_name(sbrec_chassis_by_name,
+                               get_ovs_chassis_id(ovs_table));
+
+    template_vars_update(tv_table, chassis, &tv_data->var_table,
+                         &tv_data->new, &tv_data->deleted, &tv_data->updated);
+
+    if (!sset_is_empty(&tv_data->new) || !sset_is_empty(&tv_data->deleted) ||
+            !sset_is_empty(&tv_data->updated)) {
+        engine_set_node_state(node, EN_UPDATED);
+    } else {
+        engine_set_node_state(node, EN_UNCHANGED);
+    }
+
+    tv_data->change_tracked = true;
+    return true;
+}
+
+static void
+en_template_vars_clear_tracked_data(void *data)
+{
+    struct ed_type_template_vars *tv_data = data;
+
+    sset_clear(&tv_data->new);
+    sset_clear(&tv_data->deleted);
+    sset_clear(&tv_data->updated);
+    tv_data->change_tracked = false;
+}
+
+static void
+en_template_vars_cleanup(void *data)
+{
+    struct ed_type_template_vars *tv_data = data;
+    local_templates_destroy(&tv_data->var_table);
+
+    sset_destroy(&tv_data->new);
+    sset_destroy(&tv_data->deleted);
+    sset_destroy(&tv_data->updated);
+}
+
 struct ed_type_addr_sets {
     struct shash addr_sets;
     bool change_tracked;
@@ -2706,6 +2927,9 @@ init_lflow_ctx(struct engine_node *node,
     struct ed_type_dhcp_options *dhcp_opts =
         engine_get_input_data("dhcp_options", node);
 
+    struct ed_type_template_vars *template_vars =
+        engine_get_input_data("template_vars", node);
+
     l_ctx_in->sbrec_multicast_group_by_name_datapath =
         sbrec_mc_group_by_name_dp;
     l_ctx_in->sbrec_logical_flow_by_logical_datapath =
@@ -2738,6 +2962,7 @@ init_lflow_ctx(struct engine_node *node,
     l_ctx_in->dhcp_opts = &dhcp_opts->v4_opts;
     l_ctx_in->dhcpv6_opts = &dhcp_opts->v6_opts;
     l_ctx_in->controller_event_opts = &fo->controller_event_opts;
+    l_ctx_in->template_vars = &template_vars->var_table.vars;
 
     l_ctx_out->flow_table = &fo->flow_table;
     l_ctx_out->group_table = &fo->group_table;
@@ -3064,6 +3289,64 @@ lflow_output_port_groups_handler(struct engine_node 
*node, void *data)
     return true;
 }
 
+static bool
+lflow_output_template_vars_handler(struct engine_node *node, void *data)
+{
+    struct ed_type_template_vars *tv_data =
+        engine_get_input_data("template_vars", node);
+
+    struct ed_type_lflow_output *fo = data;
+    struct lflow_ctx_out l_ctx_out;
+    struct lflow_ctx_in l_ctx_in;
+    init_lflow_ctx(node, fo, &l_ctx_in, &l_ctx_out);
+
+    const char *res_name;
+    bool changed;
+
+    if (!tv_data->change_tracked) {
+        return false;
+    }
+
+    SSET_FOR_EACH (res_name, &tv_data->deleted) {
+        if (!objdep_mgr_handle_change(l_ctx_out.lflow_deps_mgr,
+                                      OBJDEP_TYPE_TEMPLATE,
+                                      res_name, lflow_handle_changed_ref,
+                                      l_ctx_out.lflows_processed,
+                                      &l_ctx_in, &l_ctx_out, &changed)) {
+            return false;
+        }
+        if (changed) {
+            engine_set_node_state(node, EN_UPDATED);
+        }
+    }
+    SSET_FOR_EACH (res_name, &tv_data->updated) {
+        if (!objdep_mgr_handle_change(l_ctx_out.lflow_deps_mgr,
+                                      OBJDEP_TYPE_TEMPLATE,
+                                      res_name, lflow_handle_changed_ref,
+                                      l_ctx_out.lflows_processed,
+                                      &l_ctx_in, &l_ctx_out, &changed)) {
+            return false;
+        }
+        if (changed) {
+            engine_set_node_state(node, EN_UPDATED);
+        }
+    }
+    SSET_FOR_EACH (res_name, &tv_data->new) {
+        if (!objdep_mgr_handle_change(l_ctx_out.lflow_deps_mgr,
+                                      OBJDEP_TYPE_TEMPLATE,
+                                      res_name, lflow_handle_changed_ref,
+                                      l_ctx_out.lflows_processed,
+                                      &l_ctx_in, &l_ctx_out, &changed)) {
+            return false;
+        }
+        if (changed) {
+            engine_set_node_state(node, EN_UPDATED);
+        }
+    }
+
+    return true;
+}
+
 static bool
 lflow_output_runtime_data_handler(struct engine_node *node,
                                   void *data OVS_UNUSED)
@@ -3711,6 +3994,7 @@ main(int argc, char *argv[])
 
     /* Define inc-proc-engine nodes. */
     ENGINE_NODE(sb_ro, "sb_ro");
+    ENGINE_NODE_WITH_CLEAR_TRACK_DATA(template_vars, "template_vars");
     ENGINE_NODE_WITH_CLEAR_TRACK_DATA_IS_VALID(ct_zones, "ct_zones");
     ENGINE_NODE_WITH_CLEAR_TRACK_DATA(ovs_interface_shadow,
                                       "ovs_interface_shadow");
@@ -3737,6 +4021,11 @@ main(int argc, char *argv[])
 #undef OVS_NODE
 
     /* Add dependencies between inc-proc-engine nodes. */
+    engine_add_input(&en_template_vars, &en_ovs_open_vswitch,
+                     engine_noop_handler);
+    engine_add_input(&en_template_vars, &en_sb_chassis, engine_noop_handler);
+    engine_add_input(&en_template_vars, &en_sb_template_var,
+                     template_vars_sb_template_var_handler);
 
     engine_add_input(&en_addr_sets, &en_sb_address_set,
                      addr_sets_sb_address_set_handler);
@@ -3804,6 +4093,8 @@ main(int argc, char *argv[])
                      lflow_output_addr_sets_handler);
     engine_add_input(&en_lflow_output, &en_port_groups,
                      lflow_output_port_groups_handler);
+    engine_add_input(&en_lflow_output, &en_template_vars,
+                     lflow_output_template_vars_handler);
     engine_add_input(&en_lflow_output, &en_runtime_data,
                      lflow_output_runtime_data_handler);
     engine_add_input(&en_lflow_output, &en_non_vif_data,
@@ -3921,6 +4212,8 @@ main(int argc, char *argv[])
         engine_get_internal_data(&en_ct_zones);
     struct ed_type_runtime_data *runtime_data =
         engine_get_internal_data(&en_runtime_data);
+    struct ed_type_template_vars *template_vars_data =
+        engine_get_internal_data(&en_template_vars);
 
     ofctrl_init(&lflow_output_data->group_table,
                 &lflow_output_data->meter_table,
@@ -3982,6 +4275,10 @@ main(int argc, char *argv[])
                              debug_dump_lflow_conj_ids,
                              &lflow_output_data->conj_ids);
 
+    unixctl_command_register("debug/dump-local-template-vars", "", 0, 0,
+                             debug_dump_local_template_vars,
+                             &template_vars_data->var_table);
+
     unixctl_command_register("debug/ignore-startup-delay", "", 0, 0,
                              debug_ignore_startup_delay, NULL);
 
@@ -4358,9 +4655,12 @@ main(int argc, char *argv[])
                     engine_get_data(&en_addr_sets);
                 struct ed_type_port_groups *pg_data =
                     engine_get_data(&en_port_groups);
-                if (br_int && chassis && as_data && pg_data) {
+                struct ed_type_template_vars *tv_data =
+                    engine_get_data(&en_template_vars);
+                if (br_int && chassis && as_data && pg_data && tv_data) {
                     char *error = ofctrl_inject_pkt(br_int, pending_pkt.flow_s,
-                        &as_data->addr_sets, &pg_data->port_groups_cs_local);
+                        &as_data->addr_sets, &pg_data->port_groups_cs_local,
+                        &tv_data->var_table.vars);
                     if (error) {
                         unixctl_command_reply_error(pending_pkt.conn, error);
                         free(error);
@@ -4829,6 +5129,17 @@ debug_dump_lflow_conj_ids(struct unixctl_conn *conn, int 
argc OVS_UNUSED,
     ds_destroy(&conj_ids_dump);
 }
 
+static void
+debug_dump_local_template_vars(struct unixctl_conn *conn, int argc OVS_UNUSED,
+                               const char *argv[] OVS_UNUSED, void *local_vars)
+{
+    struct ds tv_str = DS_EMPTY_INITIALIZER;
+    ds_put_cstr(&tv_str, "Local template vars:\n");
+    local_templates_to_string(local_vars, &tv_str);
+    unixctl_command_reply(conn, ds_cstr(&tv_str));
+    ds_destroy(&tv_str);
+}
+
 static void
 debug_ignore_startup_delay(struct unixctl_conn *conn, int argc OVS_UNUSED,
                            const char *argv[] OVS_UNUSED, void *arg OVS_UNUSED)
diff --git a/include/ovn/expr.h b/include/ovn/expr.h
index 3b141b034..80d95ff67 100644
--- a/include/ovn/expr.h
+++ b/include/ovn/expr.h
@@ -59,6 +59,7 @@
 #include "openvswitch/match.h"
 #include "openvswitch/meta-flow.h"
 #include "logical-fields.h"
+#include "smap.h"
 
 struct ds;
 struct expr;
@@ -521,7 +522,8 @@ union expr_constant {
     char *string;
 };
 
-bool expr_constant_parse(struct lexer *, const struct expr_field *,
+bool expr_constant_parse(struct lexer *,
+                         const struct expr_field *,
                          union expr_constant *);
 void expr_constant_format(const union expr_constant *,
                           enum expr_constant_type, struct ds *);
diff --git a/include/ovn/lex.h b/include/ovn/lex.h
index ecb7ace24..38c4aa9f3 100644
--- a/include/ovn/lex.h
+++ b/include/ovn/lex.h
@@ -23,6 +23,8 @@
  * This is a simple lexical analyzer (or tokenizer) for OVN match expressions
  * and ACLs. */
 
+#include "smap.h"
+#include "sset.h"
 #include "openvswitch/meta-flow.h"
 
 struct ds;
@@ -37,7 +39,8 @@ enum lex_type {
     LEX_T_INTEGER,              /* 12345 or 1.2.3.4 or ::1 or 01:02:03:04:05 */
     LEX_T_MASKED_INTEGER,       /* 12345/10 or 1.2.0.0/16 or ::2/127 or... */
     LEX_T_MACRO,                /* $NAME */
-    LEX_T_PORT_GROUP,            /* @NAME */
+    LEX_T_PORT_GROUP,           /* @NAME */
+    LEX_T_TEMPLATE,             /* ^NAME */
     LEX_T_ERROR,                /* invalid input */
 
     /* Bare tokens. */
@@ -86,9 +89,9 @@ struct lex_token {
     /* One of LEX_*. */
     enum lex_type type;
 
-    /* Meaningful for LEX_T_ID, LEX_T_STRING, LEX_T_ERROR, LEX_T_MACRO only.
-     * For these token types, 's' may point to 'buffer'; otherwise, it points
-     * to malloc()ed memory owned by the token.
+    /* Meaningful for LEX_T_ID, LEX_T_STRING, LEX_T_ERROR, LEX_T_MACRO,
+     * LEX_T_TEMPLATE only.  For these token types, 's' may point to 'buffer';
+     * otherwise, it points to malloc()ed memory owned by the token.
      *
      * Must be NULL for other token types.
      *
@@ -151,4 +154,7 @@ void lexer_syntax_error(struct lexer *, const char 
*message, ...)
 
 char *lexer_steal_error(struct lexer *);
 
+char *lexer_parse_template_string(char *s, const struct smap *template_vars,
+                                  struct sset *template_vars_ref);
+
 #endif /* ovn/lex.h */
diff --git a/lib/actions.c b/lib/actions.c
index adbb42db4..d7d486883 100644
--- a/lib/actions.c
+++ b/lib/actions.c
@@ -258,8 +258,8 @@ add_prerequisite(struct action_context *ctx, const char 
*prerequisite)
     struct expr *expr;
     char *error;
 
-    expr = expr_parse_string(prerequisite, ctx->pp->symtab, NULL, NULL,
-                             NULL, NULL, 0, &error);
+    expr = expr_parse_string(prerequisite, ctx->pp->symtab, NULL, NULL, NULL,
+                             NULL, 0, &error);
     ovs_assert(!error);
     ctx->prereqs = expr_combine(EXPR_T_AND, ctx->prereqs, expr);
 }
@@ -4695,6 +4695,11 @@ parse_set_action(struct action_context *ctx)
 static bool
 parse_action(struct action_context *ctx)
 {
+    if (ctx->lexer->token.type == LEX_T_TEMPLATE) {
+        lexer_error(ctx->lexer, "Unexpanded template.");
+        return false;
+    }
+
     if (ctx->lexer->token.type != LEX_T_ID) {
         lexer_syntax_error(ctx->lexer, NULL);
         return false;
diff --git a/lib/expr.c b/lib/expr.c
index d1f9d28ca..43f44771c 100644
--- a/lib/expr.c
+++ b/lib/expr.c
@@ -695,7 +695,9 @@ parse_field(struct expr_context *ctx, struct expr_field *f)
         return false;
     }
 
-    symbol = shash_find_data(ctx->symtab, ctx->lexer->token.s);
+    symbol = ctx->symtab
+             ? shash_find_data(ctx->symtab, ctx->lexer->token.s)
+             : NULL;
     if (!symbol) {
         lexer_syntax_error(ctx->lexer, "expecting field name");
         return false;
@@ -894,7 +896,10 @@ parse_constant(struct expr_context *ctx, struct 
expr_constant_set *cs,
         cs->as_name = NULL;
     }
 
-    if (ctx->lexer->token.type == LEX_T_STRING) {
+    if (ctx->lexer->token.type == LEX_T_TEMPLATE) {
+        lexer_error(ctx->lexer, "Unexpanded template.");
+        return false;
+    } else if (ctx->lexer->token.type == LEX_T_STRING) {
         if (!assign_constant_set_type(ctx, cs, EXPR_C_STRING)) {
             return false;
         }
@@ -978,7 +983,9 @@ expr_constant_parse(struct lexer *lexer, const struct 
expr_field *f,
         return false;
     }
 
-    struct expr_context ctx = { .lexer = lexer };
+    struct expr_context ctx = {
+        .lexer = lexer,
+    };
 
     struct expr_constant_set cs;
     memset(&cs, 0, sizeof cs);
@@ -1332,7 +1339,10 @@ expr_parse_primary(struct expr_context *ctx, bool 
*atomic)
         return e;
     }
 
-    if (ctx->lexer->token.type == LEX_T_ID) {
+    if (ctx->lexer->token.type == LEX_T_TEMPLATE) {
+        lexer_error(ctx->lexer, "Unexpanded template.");
+        return NULL;
+    } else if (ctx->lexer->token.type == LEX_T_ID) {
         struct expr_field f;
         enum expr_relop r;
         struct expr_constant_set c;
diff --git a/lib/lex.c b/lib/lex.c
index c84d52aa8..b01a7d75c 100644
--- a/lib/lex.c
+++ b/lib/lex.c
@@ -235,6 +235,10 @@ lex_token_format(const struct lex_token *token, struct ds 
*s)
         ds_put_format(s, "@%s", token->s);
         break;
 
+    case LEX_T_TEMPLATE:
+        ds_put_format(s, "^%s", token->s);
+        break;
+
     case LEX_T_LPAREN:
         ds_put_cstr(s, "(");
         break;
@@ -588,6 +592,18 @@ lex_parse_port_group(const char *p, struct lex_token 
*token)
     return lex_parse_id(p, LEX_T_PORT_GROUP, token);
 }
 
+static const char *
+lex_parse_template(const char *p, struct lex_token *token)
+{
+    p++;
+    if (!lex_is_id1(*p)) {
+        lex_error(token, "`^' must be followed by a valid identifier.");
+        return p;
+    }
+
+    return lex_parse_id(p, LEX_T_TEMPLATE, token);
+}
+
 /* Initializes 'token' and parses the first token from the beginning of
  * null-terminated string 'p' into 'token'.  Stores a pointer to the start of
  * the token (after skipping white space and comments, if any) into '*startp'.
@@ -766,6 +782,10 @@ next:
         p = lex_parse_port_group(p, token);
         break;
 
+    case '^':
+        p = lex_parse_template(p, token);
+        break;
+
     case ':':
         if (p[1] != ':') {
             token->type = LEX_T_COLON;
@@ -1031,3 +1051,38 @@ lexer_steal_error(struct lexer *lexer)
     lexer->error = NULL;
     return error;
 }
+
+/* Takes ownership of 's' and expands all templates that are encountered
+ * in the contents of 's', if possible.  Adds the encountered template names
+ * to 'template_vars_ref'.
+ */
+char *
+lexer_parse_template_string(char *s, const struct smap *template_vars,
+                            struct sset *template_vars_ref)
+{
+    /* No '^' means no templates. */
+    if (!strchr(s, '^')) {
+        return s;
+    }
+
+    struct ds expanded = DS_EMPTY_INITIALIZER;
+
+    struct lexer lexer;
+    lexer_init(&lexer, s);
+
+    while (lexer_get(&lexer) != LEX_T_END) {
+        if (lexer.token.type == LEX_T_TEMPLATE) {
+            ds_put_cstr(&expanded, smap_get_def(template_vars, lexer.token.s,
+                                                lexer.token.s));
+            if (template_vars_ref) {
+                sset_add(template_vars_ref, lexer.token.s);
+            }
+        } else {
+            lex_token_format(&lexer.token, &expanded);
+        }
+    }
+
+    lexer_destroy(&lexer);
+    free(s);
+    return ds_steal_cstr(&expanded);
+}
\ No newline at end of file
diff --git a/lib/objdep.c b/lib/objdep.c
index 0224a5d06..0e62b88a9 100644
--- a/lib/objdep.c
+++ b/lib/objdep.c
@@ -246,6 +246,7 @@ objdep_type_name(enum objdep_type type)
         [OBJDEP_TYPE_PORTGROUP] = "Port_Group",
         [OBJDEP_TYPE_PORTBINDING] = "Port_Binding",
         [OBJDEP_TYPE_MC_GROUP] = "Multicast_Group",
+        [OBJDEP_TYPE_TEMPLATE] = "Template",
     };
 
     ovs_assert(type < OBJDEP_TYPE_MAX);
diff --git a/lib/objdep.h b/lib/objdep.h
index 059a11a62..b96c98163 100644
--- a/lib/objdep.h
+++ b/lib/objdep.h
@@ -26,6 +26,7 @@ enum objdep_type {
     OBJDEP_TYPE_PORTGROUP,
     OBJDEP_TYPE_PORTBINDING,
     OBJDEP_TYPE_MC_GROUP,
+    OBJDEP_TYPE_TEMPLATE,
     OBJDEP_TYPE_MAX,
 };
 
diff --git a/lib/ovn-util.c b/lib/ovn-util.c
index d80db179a..596e93129 100644
--- a/lib/ovn-util.c
+++ b/lib/ovn-util.c
@@ -615,6 +615,13 @@ ovn_logical_flow_hash_datapath(const struct uuid 
*logical_datapath,
     return hash_add(hash, uuid_hash(logical_datapath));
 }
 
+bool
+chassis_name_equals(const char *chassis_name,
+                    const struct sbrec_chassis *target)
+{
+    return !strcmp(chassis_name, target->name) ||
+        !strcmp(chassis_name, target->hostname);
+}
 
 struct tnlid_node {
     struct hmap_node hmap_node;
diff --git a/lib/ovn-util.h b/lib/ovn-util.h
index 145f974ed..c53d5a19a 100644
--- a/lib/ovn-util.h
+++ b/lib/ovn-util.h
@@ -29,6 +29,7 @@
 #define ROUTE_ORIGIN_STATIC "static"
 
 struct nbrec_logical_router_port;
+struct sbrec_chassis;
 struct sbrec_logical_flow;
 struct svec;
 struct uuid;
@@ -119,6 +120,8 @@ uint32_t ovn_logical_flow_hash(uint8_t table_id, enum 
ovn_pipeline pipeline,
                                const char *match, const char *actions);
 uint32_t ovn_logical_flow_hash_datapath(const struct uuid *logical_datapath,
                                         uint32_t hash);
+bool chassis_name_equals(const char *chassis_name,
+                         const struct sbrec_chassis *target);
 void ovn_conn_show(struct unixctl_conn *conn, int argc OVS_UNUSED,
                    const char *argv[] OVS_UNUSED, void *idl_);
 
diff --git a/tests/ovn.at b/tests/ovn.at
index 0dc23dbd2..ee9c7f55f 100644
--- a/tests/ovn.at
+++ b/tests/ovn.at
@@ -259,7 +259,7 @@ fe:x => error("Invalid numeric constant.")
 & => error("`&' is only valid as part of `&&'.")
 | => error("`|' is only valid as part of `||'.")
 
-^ => error("Invalid character `^' in input.")
+^ => error("`^' must be followed by a valid identifier.")
 ])
 AT_CAPTURE_FILE([input.txt])
 sed 's/ =>.*//' test-cases.txt > input.txt
diff --git a/tests/test-ovn.c b/tests/test-ovn.c
index a241f150d..7842cd915 100644
--- a/tests/test-ovn.c
+++ b/tests/test-ovn.c
@@ -291,12 +291,14 @@ test_parse_expr__(int steps)
     struct shash symtab;
     struct shash addr_sets;
     struct shash port_groups;
+    struct smap template_vars;
     struct simap ports;
     struct ds input;
 
     create_symtab(&symtab);
     create_addr_sets(&addr_sets);
     create_port_groups(&port_groups);
+    smap_init(&template_vars);
 
     simap_init(&ports);
     simap_put(&ports, "eth0", 5);
@@ -355,6 +357,7 @@ test_parse_expr__(int steps)
     shash_destroy(&addr_sets);
     expr_const_sets_destroy(&port_groups);
     shash_destroy(&port_groups);
+    smap_destroy(&template_vars);
 }
 
 static void
@@ -913,8 +916,8 @@ test_tree_shape_exhaustively(struct expr *expr, struct 
shash *symtab,
             expr_format(expr, &s);
 
             char *error;
-            modified = expr_parse_string(ds_cstr(&s), symtab, NULL,
-                                         NULL, NULL, NULL, 0, &error);
+            modified = expr_parse_string(ds_cstr(&s), symtab, NULL, NULL, NULL,
+                                         NULL, 0, &error);
             if (error) {
                 fprintf(stderr, "%s fails to parse (%s)\n",
                         ds_cstr(&s), error);
@@ -1286,6 +1289,8 @@ test_parse_actions(struct ovs_cmdl_context *ctx 
OVS_UNUSED)
     struct ds input;
     bool ok = true;
 
+    struct smap template_vars = SMAP_INITIALIZER(&template_vars);
+
     create_symtab(&symtab);
     create_gen_opts(&dhcp_opts, &dhcpv6_opts, &nd_ra_opts, &event_opts);
 
@@ -1322,7 +1327,10 @@ test_parse_actions(struct ovs_cmdl_context *ctx 
OVS_UNUSED)
             .n_tables = 24,
             .cur_ltable = 10,
         };
-        error = ovnacts_parse_string(ds_cstr(&input), &pp, &ovnacts, &prereqs);
+        char *exp_input = lexer_parse_template_string(xstrdup(ds_cstr(&input)),
+                                                      &template_vars,
+                                                      NULL);
+        error = ovnacts_parse_string(exp_input, &pp, &ovnacts, &prereqs);
         if (!error) {
             /* Convert the parsed representation back to a string and print it,
              * if it's different from the input. */
@@ -1409,6 +1417,7 @@ test_parse_actions(struct ovs_cmdl_context *ctx 
OVS_UNUSED)
         expr_destroy(prereqs);
         ovnacts_free(ovnacts.data, ovnacts.size);
         ofpbuf_uninit(&ovnacts);
+        free(exp_input);
     }
     ds_destroy(&input);
 
@@ -1419,6 +1428,7 @@ test_parse_actions(struct ovs_cmdl_context *ctx 
OVS_UNUSED)
     dhcp_opts_destroy(&dhcpv6_opts);
     nd_ra_opts_destroy(&nd_ra_opts);
     controller_event_opts_destroy(&event_opts);
+    smap_destroy(&template_vars);
     ovn_extend_table_destroy(&group_table);
     ovn_extend_table_destroy(&meter_table);
     exit(ok ? EXIT_SUCCESS : EXIT_FAILURE);
diff --git a/utilities/ovn-trace.c b/utilities/ovn-trace.c
index d9e7129d9..112dec2de 100644
--- a/utilities/ovn-trace.c
+++ b/utilities/ovn-trace.c
@@ -505,6 +505,7 @@ static struct hmap dhcp_opts;   /* Contains "struct 
gen_opts_map"s. */
 static struct hmap dhcpv6_opts; /* Contains "struct gen_opts_map"s. */
 static struct hmap nd_ra_opts; /* Contains "struct gen_opts_map"s. */
 static struct controller_event_options event_opts;
+static struct smap template_vars;
 
 static struct ovntrace_datapath *
 ovntrace_datapath_find_by_sb_uuid(const struct uuid *sb_uuid)
@@ -955,9 +956,13 @@ parse_lflow_for_datapath(const struct sbrec_logical_flow 
*sblf,
 
         char *error;
         struct expr *match;
-        match = expr_parse_string(sblf->match, &symtab, &address_sets,
+        char *match_s = lexer_parse_template_string(xstrdup(sblf->match),
+                                                    &template_vars,
+                                                    NULL);
+        match = expr_parse_string(match_s, &symtab, &address_sets,
                                   &port_groups, NULL, NULL, dp->tunnel_key,
                                   &error);
+        free(match_s);
         if (error) {
             VLOG_WARN("%s: parsing expression failed (%s)",
                       sblf->match, error);
@@ -980,7 +985,11 @@ parse_lflow_for_datapath(const struct sbrec_logical_flow 
*sblf,
         uint64_t stub[1024 / 8];
         struct ofpbuf ovnacts = OFPBUF_STUB_INITIALIZER(stub);
         struct expr *prereqs;
-        error = ovnacts_parse_string(sblf->actions, &pp, &ovnacts, &prereqs);
+        char *actions_s = lexer_parse_template_string(xstrdup(sblf->actions),
+                                                      &template_vars,
+                                                      NULL);
+        error = ovnacts_parse_string(actions_s, &pp, &ovnacts, &prereqs);
+        free(actions_s);
         if (error) {
             VLOG_WARN("%s: parsing actions failed (%s)", sblf->actions, error);
             free(error);
@@ -1078,6 +1087,7 @@ read_gen_opts(void)
     nd_ra_opts_init(&nd_ra_opts);
 
     controller_event_opts_init(&event_opts);
+    smap_init(&template_vars);
 }
 
 static void
@@ -3428,9 +3438,13 @@ trace_parse(const char *dp_s, const char *flow_s,
          *
          * First make sure that the expression parses. */
         char *error;
-        struct expr *e = expr_parse_string(flow_s, &symtab, &address_sets,
+        char *flow_exp_s = lexer_parse_template_string(xstrdup(flow_s),
+                                                       &template_vars,
+                                                       NULL);
+        struct expr *e = expr_parse_string(flow_exp_s, &symtab, &address_sets,
                                            &port_groups, NULL, NULL, 0,
                                            &error);
+        free(flow_exp_s);
         if (!e) {
             return trace_parse_error(error);
         }
@@ -3455,9 +3469,13 @@ trace_parse(const char *dp_s, const char *flow_s,
         free(port_name);
     }
 
-    char *error = expr_parse_microflow(flow_s, &symtab, &address_sets,
+    char *flow_exp_s = lexer_parse_template_string(xstrdup(flow_s),
+                                                   &template_vars,
+                                                   NULL);
+    char *error = expr_parse_microflow(flow_exp_s, &symtab, &address_sets,
                                        &port_groups, ovntrace_lookup_port,
                                        *dpp, uflow);
+    free(flow_exp_s);
     if (error) {
         return trace_parse_error(error);
     }


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