When using the --slot-settings parameter with Azure CLI's az functionapp config appsettings set command, the following behaviors should work consistently:

1. Inline Parameter Format

az functionapp config appsettings set --resource-group myRG --name myFunctionApp --slot mySlot --slot-settings "SETTING_NAME=value"

Expected Result: The setting should be created/updated with the specified value AND marked as a slot-specific setting (slotSetting: true).

2. Updating Existing Slot Settings - Key Issue

When a slot setting already exists with any value:

# Initial setting (works)
az functionapp config appsettings set --slot mySlot --slot-settings "EXISTING_SETTING=initial-value"

# Update attempts (currently failing)
az functionapp config appsettings set --slot mySlot --slot-settings "EXISTING_SETTING=updated-value"

Expected Result:

• The setting value should be updated from "initial-value" to "updated-value"
• The setting should remain as a slot-specific setting (slotSetting: true)
• The change should only affect the specified slot, not the production slot

Current Actual Result: The value remains unchanged at "initial-value"

3. JSON File Input - Array Format

az functionapp config appsettings set --resource-group myRG --name myFunctionApp --slot mySlot --slot-settings @settings.json

Where settings.json contains:

[
  {
    "name": "EXISTING_SETTING",
    "slotSetting": true,
    "value": "new-value-from-array"
  }
]

Expected Result: Existing slot settings should be updated with the new values from the JSON file.

4. JSON File Input - Object Format

az functionapp config appsettings set --resource-group myRG --name myFunctionApp --slot mySlot --slot-settings @settings.json

Where settings.json contains:

{
  "EXISTING_SETTING": "new-value-from-object"
}

Expected Result: Existing slot settings should be updated with the new values, and new settings should be automatically marked as slot-specific.

• Using --slot-settings with any format does not update existing slot settings values
• The slot configuration (slotSetting: true) is maintained, but the actual values remain unchanged
• Using --settings incorrectly updates the same settings but does change the values (though it marks them as regular settings instead of slot settings)

1. Create a Function App with a deployment slot

2. Set an initial slot setting:

   az functionapp config appsettings set --resource-group myRG --name myFunctionApp --slot mySlot --slot-settings "TEST_SETTING=initial-value"

3. Verify the setting was created:

   az functionapp config appsettings list --resource-group myRG --name myFunctionApp --slot mySlot --query "[?name=='TEST_SETTING']"

   Result: Shows {"name": "TEST_SETTING", "slotSetting": true, "value": "initial-value"}

4. Try to update using inline format:

   az functionapp config appsettings set --resource-group myRG --name myFunctionApp --slot mySlot --slot-settings "TEST_SETTING=updated-value"

5. Verify the value:

   az functionapp config appsettings list --resource-group myRG --name myFunctionApp --slot mySlot --query "[?name=='TEST_SETTING']"

   Result: Still shows {"name": "TEST_SETTING", "slotSetting": true, "value": "initial-value"} (unchanged)

6. Try to update using JSON file:

   echo '{"TEST_SETTING": "updated-via-json"}' > test.json
   az functionapp config appsettings set --resource-group myRG --name myFunctionApp --slot mySlot --slot-settings @test.json

7. Verify again - value remains unchanged

Working Workarounds

• Using --settings updates the value but incorrectly treats it as a regular setting instead of a slot setting
• Inline parameter works for creating NEW slot settings, just not for updating existing ones

Core Issue Summary

The main problem is that --slot-settings parameter:

• ✅ Works for creating new slot settings
• ❌ Fails to update existing slot settings (regardless of input format)
• ✅ Works when using --settings parameter (but incorrectly marks them as regular settings)

Impact

This bug prevents users from:

• Automating deployment pipelines that need to update slot settings
• Using configuration files to manage slot settings in CI/CD scenarios
• Properly managing slot-specific configurations in multi-environment setups

I performed a local investigation of this issue and implemented fixes that resolve the problem in my environment. Here's what I discovered:

File Investigated

src/azure-cli/azure/cli/command_modules/appservice/custom.py

Root Cause Analysis

Through my investigation, I found the issue had two main components:

1. JSON Processing: When using object format JSON {"KEY": "VALUE"}, the original code was putting values in the wrong variable (dest instead of result), so values were never applied.

2. Timing: Even when values were processed correctly, the slot configuration was updated after the application settings, so Azure didn't know the settings should be slot-specific when the values were applied.

My Local Fix 1: JSON Object Format Support

What I Found (lines ~546-556):

                if isinstance(temp, list):  # Handle array format
                    for t in temp:
                        if 'slotSetting' in t.keys():
                            slot_result[t['name']] = t['slotSetting']
                        elif setting_type == "SlotSettings":
                            slot_result[t['name']] = True
                        result[t['name']] = t['value']
                else:
                    # PROBLEM: Object format always went to 'dest', not handling SlotSettings properly
                    dest.update(temp)

My Local Fix:

                if isinstance(temp, list):  # Handle array format
                    for t in temp:
                        if 'slotSetting' in t.keys():
                            slot_result[t['name']] = t['slotSetting']
                        elif setting_type == "SlotSettings":
                            slot_result[t['name']] = True
                        result[t['name']] = t['value']
                else:
                    # Handle JSON objects - when using --slot-settings with object format,
                    # treat all keys as slot settings
                    if setting_type == "SlotSettings":
                        # For slot settings, we need to add values to result (for app settings)
                        # AND mark them as slot settings in slot_result
                        result.update(temp)  # Add actual values to result
                        for key in temp.keys():
                            slot_result[key] = True  # Mark as slot setting
                    else:
                        dest.update(temp)  # Regular settings go to dest (which is result)

My Local Fix 2: Operation Reordering

Original Code Flow (lines ~600-620):

    for setting_name, value in result.items():
        app_settings.properties[setting_name] = value
    client = web_client_factory(cmd.cli_ctx)

    # TODO: Centauri currently return wrong payload for update appsettings, remove this once backend has the fix.
    if is_centauri_functionapp(cmd, resource_group_name, name):
        update_application_settings_polling(cmd, resource_group_name, name, app_settings, slot, client)
        result = _generic_site_operation(cmd.cli_ctx, resource_group_name, name, 'list_application_settings', slot)
    else:
        result = _generic_settings_operation(cmd.cli_ctx, resource_group_name, name,
                                             'update_application_settings',
                                             app_settings, slot, client)

    # PROBLEM: slot_result was processed AFTER application settings
    app_settings_slot_cfg_names = []
    if slot_result:
        slot_cfg_names = client.web_apps.list_slot_configuration_names(resource_group_name, name)
        # ... rest of slot configuration code

My Local Modification:

    for setting_name, value in result.items():
        app_settings.properties[setting_name] = value
    client = web_client_factory(cmd.cli_ctx)

    # Process slot configurations BEFORE updating application settings
    # This ensures that slot settings are properly configured before the values are applied
    app_settings_slot_cfg_names = []
    if slot_result:
        slot_cfg_names = client.web_apps.list_slot_configuration_names(resource_group_name, name)
        slot_cfg_names.app_setting_names = slot_cfg_names.app_setting_names or []
        # Slot settings logic to add a new setting(s) or remove an existing setting(s)
        for slot_setting_name, value in slot_result.items():
            if value and slot_setting_name not in slot_cfg_names.app_setting_names:
                slot_cfg_names.app_setting_names.append(slot_setting_name)
            elif not value and slot_setting_name in slot_cfg_names.app_setting_names:
                slot_cfg_names.app_setting_names.remove(slot_setting_name)
        app_settings_slot_cfg_names = slot_cfg_names.app_setting_names
        client.web_apps.update_slot_configuration_names(resource_group_name, name, slot_cfg_names)

    # TODO: Centauri currently return wrong payload for update appsettings, remove this once backend has the fix.
    if is_centauri_functionapp(cmd, resource_group_name, name):
        update_application_settings_polling(cmd, resource_group_name, name, app_settings, slot, client)
        result = _generic_site_operation(cmd.cli_ctx, resource_group_name, name, 'list_application_settings', slot)
    else:
        result = _generic_settings_operation(cmd.cli_ctx, resource_group_name, name,
                                             'update_application_settings',
                                             app_settings, slot, client)

Results of My Local Testing

With both fixes implemented locally, all scenarios now work correctly:

• ✅ Inline Format: --slot-settings "KEY=value"
• ✅ JSON Array Format: --slot-settings @array.json
• ✅ JSON Object Format: --slot-settings @object.json
• ✅ Updating Existing Settings: Values are correctly updated and slotSetting: true is maintained

Summary of My Fixes

1. JSON Object Format Support: Added logic to handle JSON objects when setting_type == "SlotSettings" - values go to result AND keys are marked as slot settings in slot_result
2. Operation Reordering: Moved slot configuration processing to BEFORE app settings update

I discovered that both fixes were necessary - the JSON fix ensures values are properly assigned, and the timing fix ensures Azure knows they're slot settings before applying the values.