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+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+.. http://creativecommons.org/licenses/by/4.0
+
+Doctor
+^^^^^^
+
+Platform overview
+"""""""""""""""""
+
+Doctor platform provides these features in `Colorado Release <https://wiki.opnfv.org/display/SWREL/Colorado>`_:
+
+* Immediate Notification
+* Consistent resource state awareness for compute host down
+* Valid compute host status given to VM owner
+
+These features enable high availability of Network Services on top of
+the virtualized infrastructure. Immediate notification allows VNF managers
+(VNFM) to process recovery actions promptly once a failure has occurred.
+
+Consistency of resource state is necessary to execute recovery actions
+properly in the VIM.
+
+Ability to query host status gives VM owner the possibility to get
+consistent state information through an API in case of a compute host
+fault.
+
+The Doctor platform consists of the following components:
+
+* OpenStack Compute (Nova)
+* OpenStack Telemetry (Ceilometer)
+* OpenStack Alarming (Aodh)
+* Doctor Inspector
+* Doctor Monitor
+
+.. note::
+    Doctor Inspector and Monitor are sample implementations for reference.
+
+You can see an overview of the Doctor platform and how components interact in
+:numref:`figure-p1`.
+
+.. figure:: /platformoverview/images/figure-p1.png
+    :name: figure-p1
+    :width: 100%
+
+    Doctor platform and typical sequence (Colorado)
+
+Detailed information on the Doctor architecture can be found in the Doctor
+requirements documentation:
+http://artifacts.opnfv.org/doctor/docs/requirements/05-implementation.html
+
+
+Use case
+""""""""
+
+* A consumer of the NFVI wants to receive immediate notifications about faults
+  in the NFVI affecting the proper functioning of the virtual resources.
+  Therefore, such faults have to be detected as quickly as possible, and, when
+  a critical error is observed, the affected consumer is immediately informed
+  about the fault and can switch over to the STBY configuration.
+
+The faults to be monitored (and at which detection rate) will be configured by
+the consumer. Once a fault is detected, the Inspector in the Doctor
+architecture will check the resource map maintained by the Controller, to find
+out which virtual resources are affected and then update the resources state.
+The Notifier will receive the failure event requests sent from the Controller,
+and notify the consumer(s) of the affected resources according to the alarm
+configuration.
+
+Detailed workflow information is as follows:
+
+* Consumer(VNFM): (step 0) creates resources (network, server/instance) and an
+  event alarm on state down notification of that server/instance
+
+* Monitor: (step 1) periodically checks nodes, such as ping from/to each
+  dplane nic to/from gw of node, (step 2) once it fails to send out event
+  with "raw" fault event information to Inspector
+
+* Inspector: when it receives an event, it will (step 3) mark the host down
+  ("mark-host-down"), (step 4) map the PM to VM, and change the VM status to
+  down
+
+* Controller: (step 5) sends out instance update event to Ceilometer
+
+* Notifier: (step 6) Ceilometer transforms and passes the event to Aodh,
+  (step 7) Aodh will evaluate event with the registered alarm definitions,
+  then (step 8) it will fire the alarm to the "consumer" who owns the
+  instance
+
+* Consumer(VNFM): (step 9) receives the event and (step 10) recreates a new
+  instance
+
+Test case
+"""""""""
+
+Functest will call the "run.sh" script in Doctor to run the test job.
+
+The "run.sh" script will execute the following steps.
+
+Firstly, verify connectivity to target compute host according to different
+installer and prepare image for booting VM. Currently, only 'Apex' and
+'local' installer are supported.
+
+Secondly, the Doctor components are started, and, based on the above
+preparation, a test user (default as demo) will be created for the Doctor
+tests.
+
+Thirdly, the VM is booted, and an alarm event is created in Ceilometer.
+After sleeping for 1 minute in order to wait for the VM launch to complete,
+a failure is injected to the system, i.e. the network of compute host is
+disabled for 3 minutes. To ensure the host is down, the status of the host
+will be checked.
+
+Finally, the notification time, i.e. the time between the execution of step 2
+(Monitor detects failure) and step 9 (Consumer receives failure notification)
+is calculated.
+
+According to the Doctor requirements, the Doctor test is successful if the
+notification time is below 1 second.