Revert "Revert "Fix for fast/cold-boot: call db_migrator only after o…

…ld config is loaded (sonic-net#14933)" (sonic-net#15464)" (sonic-net#15684)

This reverts commit 9649a44.

files/build_templates/docker_image_ctl.j2

@@ -135,10 +135,18 @@ function postStartAction()
             $SONIC_DB_CLI CONFIG_DB SET "CONFIG_DB_INITIALIZED" "1"
         fi
 
-        if [[ -x /usr/local/bin/db_migrator.py ]]; then
-            # Migrate the DB to the latest schema version if needed
-            if [ -z "$DEV" ]; then
-                /usr/local/bin/db_migrator.py -o migrate
+        if [ -e /tmp/pending_config_migration ]; then
+            # this is first boot to a new image, config-setup execution is pending.
+            # For fast/cold reboot case, DB contains nothing at this point
+            # Call db_migrator after config-setup loads the config (from old config or minigraph)
+            echo "Delaying db_migrator until config migration is over"
+        else
+            # this is not a first time boot to a new image. Datbase container starts w/ old pre-existing config
+            if [[ -x /usr/local/bin/db_migrator.py ]]; then
+                # Migrate the DB to the latest schema version if needed
+                if [ -z "$DEV" ]; then
+                    /usr/local/bin/db_migrator.py -o migrate
+                fi
             fi
         fi
         # Add redis UDS to the redis group and give read/write access to the group

files/image_config/config-setup/config-setup

@@ -298,6 +298,16 @@ check_all_config_db_present()
     return 0   
 }
 
+# DB schema is subject to change between two images
+# Perform DB schema migration after loading backup config from previous image
+do_db_migration()
+{
+    if [[ -x /usr/local/bin/db_migrator.py ]]; then
+        # Migrate the DB to the latest schema version if needed
+        /usr/local/bin/db_migrator.py -o migrate
+    fi
+}
+
 # Perform configuration migration from backup copy.
 #  - This step is performed when a new image is installed and SONiC switch boots into it
 do_config_migration()
@@ -320,16 +330,19 @@ do_config_migration()
     if [ x"${WARM_BOOT}" == x"true" ]; then
         echo "Warm reboot detected..."
         disable_updategraph
+        do_db_migration
         rm -f /tmp/pending_config_migration
         exit 0
     elif check_all_config_db_present; then
         echo "Use config_db.json from old system..."
         reload_configdb
+        do_db_migration
         # Disable updategraph
         disable_updategraph
     elif [ -r ${MINGRAPH_FILE} ]; then
         echo "Use minigraph.xml from old system..."
         reload_minigraph
+        do_db_migration
         # Disable updategraph
         disable_updategraph
     else