Separating deployment/testing from the traffic cutover is a best practice for blue-green deployments. The idempotent cutover playbook allows for a controlled, quick, and reversible switch. A single atomic playbook is risky, slow DNS updates don’t align with typical blue-green, and a monolithic rollback process can be complex and error-prone.

The vManage API uses JSESSIONID cookies or tokens that expire. A 401 error after initial successful authentication is classic session timeout behavior. The solution is to check for session validity and re-authenticate. Disabling SSL is a security risk, RBAC issues typically cause 403 errors, and the base URL is usually the same for GUI and API.

To subscribe to DNA Center events, you must first know the status and available events. The correct flow is to verify the service, then create a subscription by specifying the event IDs (like ‘NETWORK-DEVICE-DISCOVERED’) and a destination URL where DNA Center will send HTTP POST notifications (webhook).

NETCONF subtree filters allow you to retrieve only the specific data you need from the device’s data model. Filtering at the server (device) side with XPath, as in option B, drastically reduces the amount of data transferred over the network and processed by your script compared to fetching the entire interfaces subtree.

Most Ansible network modules, including `ios_acl`, are designed to be idempotent. They work by first gathering the current state from the device (via `get` operation), comparing it to the desired state defined in the playbook, and generating a minimal set of configuration commands to align the device with the desired state. This is a core principle of Ansible.

Once secrets are committed and pushed, they exist in the repository history. Simply deleting a branch or making a new commit does not remove them from the Git object history, which can be cloned by others. The credentials must be considered exposed and revoked immediately. Subsequently, a history-rewriting tool like `git filter-repo` is necessary to completely erase the sensitive data from all commits. This is a critical security incident response.

pyATS parsers structure data hierarchically based on the CLI command. For `show ip interface brief`, the top-level key is typically ‘interfaces’. Under that, each interface name (e.g., ‘GigabitEthernet1’) is a key, containing a dictionary of attributes like ‘ip_address’, ‘interface_ok’, etc. Understanding this hierarchy is key to writing effective pyATS test scripts.

Multi-stage builds allow you to install build dependencies in a temporary image and copy only the necessary artifacts (like the Python application) to a final, slim image (e.g., `python:3.9-slim`). This reduces attack surface and size. Running as a non-root user follows the principle of least privilege, enhancing container security.

Defaults for data values should be defined in the YANG data model itself using the `default` statement. This ensures the default is applied consistently by NSO’s core system whenever the leaf is read and no value is set, regardless of the southbound protocol or template logic. It is the cleanest and most declarative approach.

Separating deployment/testing from the traffic cutover is a best practice for blue-green deployments. The idempotent cutover playbook allows for a controlled, quick, and reversible switch. A single atomic playbook is risky, slow DNS updates don’t align with typical blue-green, and a monolithic rollback process can be complex and error-prone.0