[GCU] Implementing DryRun by printing patch-sorter steps/imitating co…

…nfig_db (sonic-net#1973) #### What I did Implementing `dry-run` option flag. - Supports only printing the steps generated from patch-sorting - TODO in a future PR: Print the `SET` commands sent to `config_db` - TODO in a future PR: Print the service validation commands #### How I did it By implementing the DryRunConfigWrapper. - Whenever a dry-run is issued, the CLI output will start with `** DRY RUN EXECUTION **` - At each step we simulate `config_db`, we print a log msg starting with `** DryRun: Would ` #### How to verify it #### Previous command output (if the output of a command-line utility has changed) #### New command output (if the output of a command-line utility has changed) **Apply patch** ``` admin@vlab-01:~$ sudo config apply-patch remove-acl-table.json-patch -d -i /BGP_NEIGHBOR -i /FEATURE -i /QUEUE -i /VLAN/Vlan1000/members -i /DEVICE_METADATA -i /FLEX_COUNTER_TABLE -i /SCHEDULER ** DRY RUN EXECUTION ** Patch Applier: Patch application starting. Patch Applier: Patch: [{"op": "remove", "path": "/ACL_TABLE/DATAACL"}] Patch Applier: Getting current config db. Patch Applier: Simulating the target full config after applying the patch. Patch Applier: Validating target config does not have empty tables, since they do not show up in ConfigDb. Patch Applier: Sorting patch updates. Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, libyang[0]: Invalid JSON data (unexpected value). (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']/ports) sonic_yang(3):Data Loading Failed:Invalid JSON data (unexpected value). libyang[0]: Invalid JSON data (unexpected value). (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']/ports) sonic_yang(3):Data Loading Failed:Invalid JSON data (unexpected value). libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". Patch Applier: The patch was sorted into 7 changes: Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/policy_desc"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/stage"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL"}] Patch Applier: Applying 7 changes in order: Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/policy_desc"}] ** DryRun: Would apply [{"op": "remove", "path": "/ACL_TABLE/DATAACL/policy_desc"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] ** DryRun: Would apply [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] ** DryRun: Would apply [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] ** DryRun: Would apply [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports/0"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/stage"}] ** DryRun: Would apply [{"op": "remove", "path": "/ACL_TABLE/DATAACL/stage"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports"}] ** DryRun: Would apply [{"op": "remove", "path": "/ACL_TABLE/DATAACL/ports"}] Patch Applier: * [{"op": "remove", "path": "/ACL_TABLE/DATAACL"}] ** DryRun: Would apply [{"op": "remove", "path": "/ACL_TABLE/DATAACL"}] Patch Applier: Verifying patch updates are reflected on ConfigDB. Patch Applier: Patch application completed. Patch applied successfully. admin@vlab-01:~$ ``` **Config rollback** ``` admin@vlab-01:~$ sudo config rollback cp1 -d -i /BGP_NEIGHBOR -i /FEATURE -i /QUEUE -i /VLAN/Vlan1000/members -i /DEVICE_METADATA -i /FLEX_COUNTER_TABLE -i /SCHEDULER ** DRY RUN EXECUTION ** Config Rollbacker: Config rollbacking starting. Config Rollbacker: Checkpoint name: cp1. Config Rollbacker: Verifying 'cp1' exists. Config Rollbacker: Loading checkpoint into memory. Config Rollbacker: Replacing config using 'Config Replacer'. Config Replacer: Config replacement starting. Config Replacer: Target config length: 49881. Config Replacer: Getting current config db. Config Replacer: Generating patch between target config and current config db. Config Replacer: Applying patch using 'Patch Applier'. Patch Applier: Patch application starting. Patch Applier: Patch: [{"op": "add", "path": "/ACL_TABLE/DATAACL", "value": {"policy_desc": "DATAACL", "ports": ["PortChannel0001", "PortChannel0002", "PortChannel0003", "PortChannel0004"], "stage": "ingress", "type": "L3"}}] Patch Applier: Getting current config db. Patch Applier: Simulating the target full config after applying the patch. Patch Applier: Validating target config does not have empty tables, since they do not show up in ConfigDb. Patch Applier: Sorting patch updates. Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". Patch Applier: The patch was sorted into 7 changes: Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL", "value": {"type": "L3"}}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/policy_desc", "value": "DATAACL"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports", "value": ["PortChannel0001"]}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/1", "value": "PortChannel0002"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/2", "value": "PortChannel0003"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/3", "value": "PortChannel0004"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/stage", "value": "ingress"}] Patch Applier: Applying 7 changes in order: Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL", "value": {"type": "L3"}}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL", "value": {"type": "L3"}}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/policy_desc", "value": "DATAACL"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/policy_desc", "value": "DATAACL"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports", "value": ["PortChannel0001"]}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports", "value": ["PortChannel0001"]}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/1", "value": "PortChannel0002"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/1", "value": "PortChannel0002"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/2", "value": "PortChannel0003"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/2", "value": "PortChannel0003"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/3", "value": "PortChannel0004"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/3", "value": "PortChannel0004"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/stage", "value": "ingress"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/stage", "value": "ingress"}] Patch Applier: Verifying patch updates are reflected on ConfigDB. Patch Applier: Patch application completed. Config Replacer: Verifying config replacement is reflected on ConfigDB. Config Replacer: Config replacement completed. Config Rollbacker: Config rollbacking completed. Config rolled back successfully. admin@vlab-01:~$ ``` **Config replace** ``` admin@vlab-01:~$ sudo config replace ~/cur.json -d -i /BGP_NEIGHBOR -i /FEATURE -i /QUEUE -i /VLAN/Vlan1000/members -i /DEVICE_METADATA -i /FLEX_COUNTER_TABLE -i /SCHEDULER -d ** DRY RUN EXECUTION ** Config Replacer: Config replacement starting. Config Replacer: Target config length: 49881. Config Replacer: Getting current config db. Config Replacer: Generating patch between target config and current config db. Config Replacer: Applying patch using 'Patch Applier'. Patch Applier: Patch application starting. Patch Applier: Patch: [{"op": "add", "path": "/ACL_TABLE/DATAACL", "value": {"policy_desc": "DATAACL", "ports": ["PortChannel0001", "PortChannel0002", "PortChannel0003", "PortChannel0004"], "stage": "ingress", "type": "L3"}}] Patch Applier: Getting current config db. Patch Applier: Simulating the target full config after applying the patch. Patch Applier: Validating target config does not have empty tables, since they do not show up in ConfigDb. Patch Applier: Sorting patch updates. Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, Note: Below table(s) have no YANG models: BGP_PEER_RANGE, CABLE_LENGTH, CONSOLE_SWITCH, DEVICE_NEIGHBOR_METADATA, DHCP_SERVER, KDUMP, RESTAPI, SNMP, SNMP_COMMUNITY, SYSLOG_SERVER, TELEMETRY, libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". libyang[0]: Missing required element "type" in "ACL_TABLE_LIST". (path: /sonic-acl:sonic-acl/ACL_TABLE/ACL_TABLE_LIST[ACL_TABLE_NAME='DATAACL']) sonic_yang(3):Data Loading Failed:Missing required element "type" in "ACL_TABLE_LIST". Patch Applier: The patch was sorted into 7 changes: Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL", "value": {"type": "L3"}}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/policy_desc", "value": "DATAACL"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports", "value": ["PortChannel0001"]}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/1", "value": "PortChannel0002"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/2", "value": "PortChannel0003"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/3", "value": "PortChannel0004"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/stage", "value": "ingress"}] Patch Applier: Applying 7 changes in order: Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL", "value": {"type": "L3"}}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL", "value": {"type": "L3"}}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/policy_desc", "value": "DATAACL"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/policy_desc", "value": "DATAACL"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports", "value": ["PortChannel0001"]}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports", "value": ["PortChannel0001"]}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/1", "value": "PortChannel0002"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/1", "value": "PortChannel0002"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/2", "value": "PortChannel0003"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/2", "value": "PortChannel0003"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/3", "value": "PortChannel0004"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/ports/3", "value": "PortChannel0004"}] Patch Applier: * [{"op": "add", "path": "/ACL_TABLE/DATAACL/stage", "value": "ingress"}] ** DryRun: Would apply [{"op": "add", "path": "/ACL_TABLE/DATAACL/stage", "value": "ingress"}] Patch Applier: Verifying patch updates are reflected on ConfigDB. Patch Applier: Patch application completed. Config Replacer: Verifying config replacement is reflected on ConfigDB. Config Replacer: Config replacement completed. Config replaced successfully. admin@vlab-01:~$ ```
vivekrnv · Dec 17, 2021 · 818dcbf · 818dcbf
1 parent fe00bbf
commit 818dcbf
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Showing 7 changed files with 130 additions and 8 deletions.
diff --git a/config/main.py b/config/main.py
@@ -1164,6 +1164,10 @@ def load(filename, yes):
         log.log_info("'load' executing...")
         clicommon.run_command(command, display_cmd=True)
 
+def print_dry_run_message(dry_run):
+    if dry_run:
+        click.secho("** DRY RUN EXECUTION **", fg="yellow", underline=True)
+
 @config.command('apply-patch')
 @click.argument('patch-file-path', type=str, required=True)
 @click.option('-f', '--format', type=click.Choice([e.name for e in ConfigFormat]),
@@ -1182,6 +1186,8 @@ def apply_patch(ctx, patch_file_path, format, dry_run, ignore_non_yang_tables, i
 
        <patch-file-path>: Path to the patch file on the file-system."""
     try:
+        print_dry_run_message(dry_run)
+
         with open(patch_file_path, 'r') as fh:
             text = fh.read()
             patch_as_json = json.loads(text)
@@ -1214,6 +1220,8 @@ def replace(ctx, target_file_path, format, dry_run, ignore_non_yang_tables, igno
 
        <target-file-path>: Path to the target file on the file-system."""
     try:
+        print_dry_run_message(dry_run)
+
         with open(target_file_path, 'r') as fh:
             target_config_as_text = fh.read()
             target_config = json.loads(target_config_as_text)
@@ -1241,6 +1249,8 @@ def rollback(ctx, checkpoint_name, dry_run, ignore_non_yang_tables, ignore_path,
 
        <checkpoint-name>: The checkpoint name, use `config list-checkpoints` command to see available checkpoints."""
     try:
+        print_dry_run_message(dry_run)
+
         GenericUpdater().rollback(checkpoint_name, verbose, dry_run, ignore_non_yang_tables, ignore_path)
 
         click.secho("Config rolled back successfully.", fg="cyan", underline=True)

diff --git a/generic_config_updater/change_applier.py b/generic_config_updater/change_applier.py
@@ -55,6 +55,16 @@ def prune_empty_table(data):
     return data
 
 
+class DryRunChangeApplier:
+
+    def __init__(self, config_wrapper):
+        self.config_wrapper = config_wrapper
+
+
+    def apply(self, change):
+        self.config_wrapper.apply_change_to_config_db(change)
+
+
 class ChangeApplier:
 
     updater_conf = None

diff --git a/generic_config_updater/generic_updater.py b/generic_config_updater/generic_updater.py
@@ -5,7 +5,7 @@
                        DryRunConfigWrapper, PatchWrapper, genericUpdaterLogging
 from .patch_sorter import StrictPatchSorter, NonStrictPatchSorter, ConfigSplitter, \
                           TablesWithoutYangConfigSplitter, IgnorePathsFromYangConfigSplitter
-from .change_applier import ChangeApplier
+from .change_applier import ChangeApplier, DryRunChangeApplier
 
 CHECKPOINTS_DIR = "/etc/sonic/checkpoints"
 CHECKPOINT_EXT = ".cp.json"
@@ -299,9 +299,13 @@ class GenericUpdateFactory:
     def create_patch_applier(self, config_format, verbose, dry_run, ignore_non_yang_tables, ignore_paths):
         self.init_verbose_logging(verbose)
         config_wrapper = self.get_config_wrapper(dry_run)
+        change_applier = self.get_change_applier(dry_run, config_wrapper)
         patch_wrapper = PatchWrapper(config_wrapper)
         patch_sorter = self.get_patch_sorter(ignore_non_yang_tables, ignore_paths, config_wrapper, patch_wrapper)
-        patch_applier = PatchApplier(config_wrapper=config_wrapper, patchsorter=patch_sorter, patch_wrapper=patch_wrapper)
+        patch_applier = PatchApplier(config_wrapper=config_wrapper,
+                                     patchsorter=patch_sorter,
+                                     patch_wrapper=patch_wrapper,
+                                     changeapplier=change_applier)
 
         if config_format == ConfigFormat.CONFIGDB:
             pass
@@ -320,9 +324,13 @@ def create_config_replacer(self, config_format, verbose, dry_run, ignore_non_yan
         self.init_verbose_logging(verbose)
 
         config_wrapper = self.get_config_wrapper(dry_run)
+        change_applier = self.get_change_applier(dry_run, config_wrapper)
         patch_wrapper = PatchWrapper(config_wrapper)
         patch_sorter = self.get_patch_sorter(ignore_non_yang_tables, ignore_paths, config_wrapper, patch_wrapper)
-        patch_applier = PatchApplier(config_wrapper=config_wrapper, patchsorter=patch_sorter, patch_wrapper=patch_wrapper)
+        patch_applier = PatchApplier(config_wrapper=config_wrapper,
+                                     patchsorter=patch_sorter,
+                                     patch_wrapper=patch_wrapper,
+                                     changeapplier=change_applier)
 
         config_replacer = ConfigReplacer(patch_applier=patch_applier, config_wrapper=config_wrapper)
         if config_format == ConfigFormat.CONFIGDB:
@@ -342,9 +350,13 @@ def create_config_rollbacker(self, verbose, dry_run=False, ignore_non_yang_table
         self.init_verbose_logging(verbose)
 
         config_wrapper = self.get_config_wrapper(dry_run)
+        change_applier = self.get_change_applier(dry_run, config_wrapper)
         patch_wrapper = PatchWrapper(config_wrapper)
         patch_sorter = self.get_patch_sorter(ignore_non_yang_tables, ignore_paths, config_wrapper, patch_wrapper)
-        patch_applier = PatchApplier(config_wrapper=config_wrapper, patchsorter=patch_sorter, patch_wrapper=patch_wrapper)
+        patch_applier = PatchApplier(config_wrapper=config_wrapper,
+                                     patchsorter=patch_sorter,
+                                     patch_wrapper=patch_wrapper,
+                                     changeapplier=change_applier)
 
         config_replacer = ConfigReplacer(config_wrapper=config_wrapper, patch_applier=patch_applier)
         config_rollbacker = FileSystemConfigRollbacker(config_wrapper = config_wrapper, config_replacer = config_replacer)
@@ -363,6 +375,12 @@ def get_config_wrapper(self, dry_run):
         else:
             return ConfigWrapper()
 
+    def get_change_applier(self, dry_run, config_wrapper):
+        if dry_run:
+            return DryRunChangeApplier(config_wrapper)
+        else:
+            return ChangeApplier()
+
     def get_patch_sorter(self, ignore_non_yang_tables, ignore_paths, config_wrapper, patch_wrapper):
         if not ignore_non_yang_tables and not ignore_paths:
             return StrictPatchSorter(config_wrapper, patch_wrapper)

diff --git a/generic_config_updater/gu_common.py b/generic_config_updater/gu_common.py
@@ -152,9 +152,26 @@ def remove_empty_tables(self, config):
         return config_with_non_empty_tables
 
 class DryRunConfigWrapper(ConfigWrapper):
-    # TODO: implement DryRunConfigWrapper
     # This class will simulate all read/write operations to ConfigDB on a virtual storage unit.
-    pass
+    def __init__(self, initial_imitated_config_db = None):
+        super().__init__()
+        self.logger = genericUpdaterLogging.get_logger(title="** DryRun", print_all_to_console=True)
+        self.imitated_config_db = copy.deepcopy(initial_imitated_config_db)
+
+    def apply_change_to_config_db(self, change):
+        self._init_imitated_config_db_if_none()
+        self.logger.log_notice(f"Would apply {change}")
+        self.imitated_config_db = change.apply(self.imitated_config_db)
+
+    def get_config_db_as_json(self):
+        self._init_imitated_config_db_if_none()
+        return self.imitated_config_db
+
+    def _init_imitated_config_db_if_none(self):
+        # if there is no initial imitated config_db and it is the first time calling this method
+        if self.imitated_config_db is None:
+            self.imitated_config_db = super().get_config_db_as_json()
+
 
 class PatchWrapper:
     def __init__(self, config_wrapper=None):

diff --git a/tests/generic_config_updater/change_applier_test.py b/tests/generic_config_updater/change_applier_test.py
@@ -4,7 +4,7 @@
 import os
 import unittest
 from collections import defaultdict
-from unittest.mock import patch
+from unittest.mock import patch, Mock, call
 
 import generic_config_updater.change_applier
 import generic_config_updater.services_validator
@@ -269,4 +269,16 @@ def test_change_apply(self, mock_set, mock_db, mock_os_sys):
         debug_print("all good for applier")
 
 
-
+class TestDryRunChangeApplier(unittest.TestCase):
+    def test_apply__calls_apply_change_to_config_db(self):
+        # Arrange
+        change = Mock()
+        config_wrapper = Mock()
+        applier = generic_config_updater.change_applier.DryRunChangeApplier(config_wrapper)
+
+        # Act
+        applier.apply(change)
+
+        # Assert
+        applier.config_wrapper.apply_change_to_config_db.assert_has_calls([call(change)])
+
diff --git a/tests/generic_config_updater/generic_updater_test.py b/tests/generic_config_updater/generic_updater_test.py
@@ -7,6 +7,7 @@
 
 import generic_config_updater.generic_updater as gu
 import generic_config_updater.patch_sorter as ps
+import generic_config_updater.change_applier as ca
 
 # import sys
 # sys.path.insert(0,'../../generic_config_updater')
@@ -420,8 +421,11 @@ def validate_create_patch_applier(self, params, expected_decorators):
         self.assertIsInstance(patch_applier, gu.PatchApplier)
         if params["dry_run"]:
             self.assertIsInstance(patch_applier.config_wrapper, gu.DryRunConfigWrapper)
+            self.assertIsInstance(patch_applier.changeapplier, ca.DryRunChangeApplier)
+            self.assertIsInstance(patch_applier.changeapplier.config_wrapper, gu.DryRunConfigWrapper)
         else:
             self.assertIsInstance(patch_applier.config_wrapper, gu.ConfigWrapper)
+            self.assertIsInstance(patch_applier.changeapplier, ca.ChangeApplier)
 
         if params["ignore_non_yang_tables"] or params["ignore_paths"]:
             self.assertIsInstance(patch_applier.patchsorter, ps.NonStrictPatchSorter)
@@ -451,9 +455,12 @@ def validate_create_config_replacer(self, params, expected_decorators):
         if params["dry_run"]:
             self.assertIsInstance(config_replacer.config_wrapper, gu.DryRunConfigWrapper)
             self.assertIsInstance(config_replacer.patch_applier.config_wrapper, gu.DryRunConfigWrapper)
+            self.assertIsInstance(config_replacer.patch_applier.changeapplier, ca.DryRunChangeApplier)
+            self.assertIsInstance(config_replacer.patch_applier.changeapplier.config_wrapper, gu.DryRunConfigWrapper)
         else:
             self.assertIsInstance(config_replacer.config_wrapper, gu.ConfigWrapper)
             self.assertIsInstance(config_replacer.patch_applier.config_wrapper, gu.ConfigWrapper)
+            self.assertIsInstance(config_replacer.patch_applier.changeapplier, ca.ChangeApplier)
 
         if params["ignore_non_yang_tables"] or params["ignore_paths"]:
             self.assertIsInstance(config_replacer.patch_applier.patchsorter, ps.NonStrictPatchSorter)
@@ -482,11 +489,15 @@ def validate_create_config_rollbacker(self, params, expected_decorators):
             self.assertIsInstance(config_rollbacker.config_replacer.config_wrapper, gu.DryRunConfigWrapper)
             self.assertIsInstance(
                 config_rollbacker.config_replacer.patch_applier.config_wrapper, gu.DryRunConfigWrapper)
+            self.assertIsInstance(config_rollbacker.config_replacer.patch_applier.changeapplier, ca.DryRunChangeApplier)
+            self.assertIsInstance(
+                config_rollbacker.config_replacer.patch_applier.changeapplier.config_wrapper, gu.DryRunConfigWrapper)
         else:
             self.assertIsInstance(config_rollbacker.config_wrapper, gu.ConfigWrapper)
             self.assertIsInstance(config_rollbacker.config_replacer.config_wrapper, gu.ConfigWrapper)
             self.assertIsInstance(
                 config_rollbacker.config_replacer.patch_applier.config_wrapper, gu.ConfigWrapper)
+            self.assertIsInstance(config_rollbacker.config_replacer.patch_applier.changeapplier, ca.ChangeApplier)
 
         if params["ignore_non_yang_tables"] or params["ignore_paths"]:
             self.assertIsInstance(config_rollbacker.config_replacer.patch_applier.patchsorter, ps.NonStrictPatchSorter)

diff --git a/tests/generic_config_updater/gu_common_test.py b/tests/generic_config_updater/gu_common_test.py
@@ -7,6 +7,50 @@
 from .gutest_helpers import create_side_effect_dict, Files
 import generic_config_updater.gu_common as gu_common
 
+class TestDryRunConfigWrapper(unittest.TestCase):
+    def test_get_config_db_as_json__returns_imitated_config_db(self):
+        # Arrange
+        config_wrapper = gu_common.DryRunConfigWrapper(Files.CONFIG_DB_AS_JSON)
+        expected = Files.CONFIG_DB_AS_JSON
+
+        # Act
+        actual = config_wrapper.get_config_db_as_json()
+
+        # Assert
+        self.assertDictEqual(expected, actual)
+
+    def test_get_sonic_yang_as_json__returns_imitated_config_db_as_yang(self):
+        # Arrange
+        config_wrapper = gu_common.DryRunConfigWrapper(Files.CONFIG_DB_AS_JSON)
+        expected = Files.SONIC_YANG_AS_JSON
+
+        # Act
+        actual = config_wrapper.get_sonic_yang_as_json()
+
+        # Assert
+        self.assertDictEqual(expected, actual)
+
+    def test_apply_change_to_config_db__multiple_calls__changes_imitated_config_db(self):
+        # Arrange
+        imitated_config_db = Files.CONFIG_DB_AS_JSON
+        config_wrapper = gu_common.DryRunConfigWrapper(imitated_config_db)
+
+        changes = [gu_common.JsonChange(jsonpatch.JsonPatch([{'op':'remove', 'path':'/VLAN'}])),
+                   gu_common.JsonChange(jsonpatch.JsonPatch([{'op':'remove', 'path':'/ACL_TABLE'}])),
+                   gu_common.JsonChange(jsonpatch.JsonPatch([{'op':'remove', 'path':'/PORT'}]))
+                  ]
+
+        expected = imitated_config_db
+        for change in changes:
+            # Act
+            config_wrapper.apply_change_to_config_db(change)
+
+            actual = config_wrapper.get_config_db_as_json()
+            expected = change.apply(expected)
+
+            # Assert
+            self.assertDictEqual(expected, actual)
+
 class TestConfigWrapper(unittest.TestCase):
     def setUp(self):
         self.config_wrapper_mock = gu_common.ConfigWrapper()