Merge pull request #196974 from adwilso/patch-4

denrea · web-flow · commit b04c3153777d · 2022-05-06T14:16:52.000-07:00
Scheduled Events Windows Improvements
diff --git a/articles/virtual-machines/windows/scheduled-events.md b/articles/virtual-machines/windows/scheduled-events.md
@@ -40,10 +40,10 @@ With Scheduled Events, your application can discover when maintenance will occur
 
 Scheduled Events provides events in the following use cases:
 
-- [Platform initiated maintenance](../maintenance-and-updates.md?bc=/azure/virtual-machines/windows/breadcrumb/toc.json&toc=/azure/virtual-machines/windows/toc.json) (for example, VM reboot, live migration or memory preserving updates for host)
-- Virtual machine is running on [degraded host hardware](https://azure.microsoft.com/blog/find-out-when-your-virtual-machine-hardware-is-degraded-with-scheduled-events) that is predicted to fail soon
-- Virtual machine was running on a host that suffered a hardware failure
-- User-initiated maintenance (for example, a user restarts or redeploys a VM)
+- [Platform initiated maintenance](../maintenance-and-updates.md?bc=/azure/virtual-machines/windows/breadcrumb/toc.json&toc=/azure/virtual-machines/windows/toc.json) (for example, VM reboot, live migration or memory preserving updates for host).
+- Virtual machine is running on [degraded host hardware](https://azure.microsoft.com/blog/find-out-when-your-virtual-machine-hardware-is-degraded-with-scheduled-events) that is predicted to fail soon.
+- Virtual machine was running on a host that suffered a hardware failure.
+- User-initiated maintenance (for example, a user restarts or redeploys a VM).
 - [Spot VM](../spot-vms.md) and [Spot scale set](../../virtual-machine-scale-sets/use-spot.md) instance evictions.
 
 ## The Basics  
@@ -97,7 +97,7 @@ Scheduled Events is disabled for your service if it does not make a request for
 ### User-initiated maintenance
 User-initiated VM maintenance via the Azure portal, API, CLI, or PowerShell results in a scheduled event. You then can test the maintenance preparation logic in your application, and your application can prepare for user-initiated maintenance.
 
-If you restart a VM, an event with the type `Reboot` is scheduled. If you redeploy a VM, an event with the type `Redeploy` is scheduled.
+If you restart a VM, an event with the type `Reboot` is scheduled. If you redeploy a VM, an event with the type `Redeploy` is scheduled. Typically events with a user event source can be immediately approved to avoid a delay on user-initiated actions. 
 
 ## Use the API
 
@@ -115,6 +115,22 @@ curl -H Metadata:true http://169.254.169.254/metadata/scheduledevents?api-versio
 ```
 Invoke-RestMethod -Headers @{"Metadata"="true"} -Method GET -Uri "http://169.254.169.254/metadata/scheduledevents?api-version=2020-07-01" | ConvertTo-Json -Depth 64
 ```
+#### Python sample
+````
+import json
+import requests
+
+metadata_url ="http://169.254.169.254/metadata/scheduledevents"
+header = {'Metadata' : 'true'}
+query_params = {'api-version':'2020-07-01'}
+
+def get_scheduled_events():           
+    resp = requests.get(metadata_url, headers = header, params = query_params)
+    data = resp.json()
+    return data
+
+````
+
 
 A response contains an array of scheduled events. An empty array means that currently no events are scheduled.
 In the case where there are scheduled events, the response contains an array of events. 
@@ -140,13 +156,13 @@ In the case where there are scheduled events, the response contains an array of
 ### Event properties
 |Property  |  Description |
 | - | - |
-| Document Incarnation | Integer that increases when the events contained in the array of scheduled events changes. Documents with the same incarnation contain the same event information, and the incarnation will be incremented when an event changes. |
+| Document Incarnation | Integer that increases when the events array changes. Documents with the same incarnation contain the same event information, and the incarnation will be incremented when an event changes. |
 | EventId | Globally unique identifier for this event. <br><br> Example: <br><ul><li>602d9444-d2cd-49c7-8624-8643e7171297  |
 | EventType | Impact this event causes. <br><br> Values: <br><ul><li> `Freeze`: The Virtual Machine is scheduled to pause for a few seconds. CPU and network connectivity may be suspended, but there is no impact on memory or open files.<li>`Reboot`: The Virtual Machine is scheduled for reboot (non-persistent memory is lost). <li>`Redeploy`: The Virtual Machine is scheduled to move to another node (ephemeral disks are lost). <li>`Preempt`: The Spot Virtual Machine is being deleted (ephemeral disks are lost). This event is made available on a best effort basis <li> `Terminate`: The virtual machine is scheduled to be deleted. |
 | ResourceType | Type of resource this event affects. <br><br> Values: <ul><li>`VirtualMachine`|
 | Resources| List of resources this event affects. The list is guaranteed to contain machines from at most one [update domain](../availability.md), but it might not contain all machines in the UD. <br><br> Example: <br><ul><li> ["FrontEnd_IN_0", "BackEnd_IN_0"] |
 | EventStatus | Status of this event. <br><br> Values: <ul><li>`Scheduled`: This event is scheduled to start after the time specified in the `NotBefore` property.<li>`Started`: This event has started.</ul> No `Completed` or similar status is ever provided. The event is no longer returned when the event is finished.
-| NotBefore| Time after which this event can start. The event is guaranteed to not start before this time. <br><br> Example: <br><ul><li> Mon, 19 Sep 2016 18:29:47 GMT  |
+| NotBefore| Time after which this event can start. The event is guaranteed to not start before this time. Will be blank if the event has already started <br><br> Example: <br><ul><li> Mon, 19 Sep 2016 18:29:47 GMT  |
 | Description | Description of this event. <br><br> Example: <br><ul><li> Host server is undergoing maintenance. |
 | EventSource | Initiator of the event. <br><br> Example: <br><ul><li> `Platform`: This event is initiated by platform. <li>`User`: This event is initiated by user. |
 | DurationInSeconds | The expected duration of the interruption caused by the event. <br><br> Example: <br><ul><li> `9`: The interruption caused by the event will last for 9 seconds. <li>`-1`: The default value used if the impact duration is either unknown or not applicable. |
@@ -164,18 +180,20 @@ Each event is scheduled a minimum amount of time in the future based on the even
 
 > [!NOTE] 
 > In some cases, Azure is able to predict host failure due to degraded hardware and will attempt to mitigate disruption to your service by scheduling a migration. Affected virtual machines will receive a scheduled event with a `NotBefore` that is typically a few days in the future. The actual time varies depending on the predicted failure risk assessment. Azure tries to give 7 days' advance notice when possible, but the actual time varies and might be smaller if the prediction is that there is a high chance of the hardware failing imminently. To minimize risk to your service in case the hardware fails before the system-initiated migration, we recommend that you self-redeploy your virtual machine as soon as possible.
+
 >[!NOTE]
-> In the case the host node experiences a hardware failure Azure will bypass the minimum notice period an immediately begin the recovery process for affected virtual machines. This reduces recovery time in the case that the affected VMs are unable to respond. During the recovery process an event will be created for all impacted VMs with EventType = Reboot and EventStatus = Started
+> In the case the host node experiences a hardware failure Azure will bypass the minimum notice period an immediately begin the recovery process for affected virtual machines. This reduces recovery time in the case that the affected VMs are unable to respond. During the recovery process an event will be created for all impacted VMs with `EventType = Reboot` and `EventStatus = Started`.
 
 ### Polling frequency
 
 You can poll the endpoint for updates as frequently or infrequently as you like. However, the longer the time between requests, the more time you potentially lose to react to an upcoming event. Most events have 5 to 15 minutes of advance notice, although in some cases advance notice might be as little as 30 seconds. To ensure that you have as much time as possible to take mitigating actions, we recommend that you poll the service once per second.
 
 ### Start an event 
 
-After you learn of an upcoming event and finish your logic for graceful shutdown, you can approve the outstanding event by making a `POST` call to Metadata Service with `EventId`. This call indicates to Azure that it can shorten the minimum notification time (when possible). 
+After you learn of an upcoming event and finish your logic for graceful shutdown, you can approve the outstanding event by making a `POST` call to Metadata Service with `EventId`. This call indicates to Azure that it can shorten the minimum notification time (when possible). The event may not start immediately upon approval, in some cases Azure will require the approval of all the VMs hosted on the node before proceeding with the event. 
 
 The following JSON sample is expected in the `POST` request body. The request should contain a list of `StartRequests`. Each `StartRequest` contains `EventId` for the event you want to expedite:
+
 ```
 {
 	"StartRequests" : [
@@ -186,6 +204,9 @@ The following JSON sample is expected in the `POST` request body. The request sh
 }
 ```
 
+The service will always return a 200 success code in the case of a valid event ID, even if it was already approved by a different VM. A 400 error code indicates that the request header or payload was malformed. 
+
+
 #### Bash sample
 ```
 curl -H Metadata:true -X POST -d '{"StartRequests": [{"EventId": "f020ba2e-3bc0-4c40-a10b-86575a9eabd5"}]}' http://169.254.169.254/metadata/scheduledevents?api-version=2020-07-01
@@ -194,63 +215,184 @@ curl -H Metadata:true -X POST -d '{"StartRequests": [{"EventId": "f020ba2e-3bc0-
 ```
 Invoke-RestMethod -Headers @{"Metadata" = "true"} -Method POST -body '{"StartRequests": [{"EventId": "5DD55B64-45AD-49D3-BBC9-F57D4EA97BD7"}]}' -Uri http://169.254.169.254/metadata/scheduledevents?api-version=2020-07-01 | ConvertTo-Json -Depth 64
 ```
+#### Python sample
+````
+import json
+import requests
+
+def confirm_scheduled_event(event_id):  
+   # This payload confirms a single event with id event_id
+   payload = json.dumps({"StartRequests": [{"EventId": event_id }]})
+   response = requests.post("http://169.254.169.254/metadata/scheduledevents", 
+                            headers =  {'Metadata' : 'true'}, 
+                            params = {'api-version':'2020-07-01'}, 
+                            data = payload)    
+   return response.status_code
+````
 
 > [!NOTE] 
 > Acknowledging an event allows the event to proceed for all `Resources` in the event, not just the VM that acknowledges the event. Therefore, you can choose to elect a leader to coordinate the acknowledgement, which might be as simple as the first machine in the `Resources` field.
 
-## Python Sample 
+## Example responses
+The following is an example of a series of events that were seen by two VMs that were live migrated to another node. 
 
-The following sample queries Metadata Service for scheduled events and approves each outstanding event:
+The `DocumentIncarnation` is changing every time there is new information in `Events`. An approval of the event would allow the freeze to proceed for both WestNO_0 and WestNO_1. The `DurationInSeconds` of -1 indicates that the platform does not know how long the operation will take. 
 
-```python
-#!/usr/bin/python
+```JSON
+{
+    "DocumentIncarnation":  1,
+    "Events":  [
+               ]
+}
 
-import json
-import socket
-import urllib2
+{
+    "DocumentIncarnation":  2,
+    "Events":  [
+                   {
+                       "EventId":  "C7061BAC-AFDC-4513-B24B-AA5F13A16123",
+                       "EventStatus":  "Scheduled",
+                       "EventType":  "Freeze",
+                       "ResourceType":  "VirtualMachine",
+                       "Resources":  [
+                                         "WestNO_0",
+                                         "WestNO_1"
+                                     ],
+                       "NotBefore":  "Mon, 11 Apr 2022 22:26:58 GMT",
+                       "Description":  "Virtual machine is being paused because of a memory-preserving Live Migration operation.",
+                       "EventSource":  "Platform",
+                       "DurationInSeconds":  -1
+                   }
+               ]
+}
 
-metadata_url = "http://169.254.169.254/metadata/scheduledevents?api-version=2020-07-01"
-this_host = socket.gethostname()
+{
+    "DocumentIncarnation":  3,
+    "Events":  [
+                   {
+                       "EventId":  "C7061BAC-AFDC-4513-B24B-AA5F13A16123",
+                       "EventStatus":  "Started",
+                       "EventType":  "Freeze",
+                       "ResourceType":  "VirtualMachine",
+                       "Resources":  [
+                                         "WestNO_0",
+                                         "WestNO_1"
+                                     ],
+                       "NotBefore":  "",
+                       "Description":  "Virtual machine is being paused because of a memory-preserving Live Migration operation.",
+                       "EventSource":  "Platform",
+                       "DurationInSeconds":  -1
+                   }
+               ]
+}
 
+{
+    "DocumentIncarnation":  4,
+    "Events":  [
+               ]
+}
 
-def get_scheduled_events():
-    req = urllib2.Request(metadata_url)
-    req.add_header('Metadata', 'true')
-    resp = urllib2.urlopen(req)
-    data = json.loads(resp.read())
-    return data
+```
 
+## Python Sample 
+
+The following sample queries Metadata Service for scheduled events and approves each outstanding event:
 
-def handle_scheduled_events(data):
-    for evt in data['Events']:
-        eventid = evt['EventId']
-        status = evt['EventStatus']
-        resources = evt['Resources']
-        eventtype = evt['EventType']
-        resourcetype = evt['ResourceType']
-        notbefore = evt['NotBefore'].replace(" ", "_")
-	description = evt['Description']
-	eventSource = evt['EventSource']
-        if this_host in resources:
-            print("+ Scheduled Event. This host " + this_host +
-                " is scheduled for " + eventtype + 
-		" by " + eventSource + 
-		" with description " + description +
-		" not before " + notbefore)
-            # Add logic for handling events here
+```python
+#!/usr/bin/python
+import json
+import requests
+from time import sleep
+
+# The URL to access the metadata service
+metadata_url ="http://169.254.169.254/metadata/scheduledevents"
+# This must be sent otherwise the request will be ignored
+header = {'Metadata' : 'true'}
+# Current version of the API
+query_params = {'api-version':'2020-07-01'}
+
+def get_scheduled_events():           
+    resp = requests.get(metadata_url, headers = header, params = query_params)
+    data = resp.json()
+    return data
 
+def confirm_scheduled_event(event_id):  
+    # This payload confirms a single event with id event_id
+    # You can confirm multiple events in a single request if needed      
+    payload = json.dumps({"StartRequests": [{"EventId": event_id }]})
+    response = requests.post(metadata_url, 
+                            headers= header,
+                            params = query_params, 
+                            data = payload)    
+    return response.status_code
+
+def log(event): 
+    # This is an optional placeholder for logging events to your system 
+    print(event["Description"])
+    return
+
+def advanced_sample(last_document_incarnation): 
+    # Poll every second to see if there are new scheduled events to process
+    # Since some events may have necessarily short warning periods, it is 
+    # recommended to poll frequently
+    found_document_incarnation = last_document_incarnation
+    while (last_document_incarnation == found_document_incarnation):
+        sleep(1)
+        payload = get_scheduled_events()    
+        found_document_incarnation = payload["DocumentIncarnation"]        
+        
+    # We recommend processing all events in a document together, 
+    # even if you won't be actioning on them right away
+    for event in payload["Events"]:
+
+        # Events that have already started, logged for tracking
+        if (event["EventStatus"] == "Started"):
+            log(event)
+            
+        # Approve all user initiated events. These are typically created by an 
+        # administrator and approving them immediately can help to avoid delays 
+        # in admin actions
+        elif (event["EventSource"] == "User"):
+            confirm_scheduled_event(event["EventId"])            
+            
+        # For this application, freeze events less that 9 seconds are considered
+        # no impact. This will immediately approve them
+        elif (event["EventType"] == "Freeze" and 
+            int(event["DurationInSeconds"]) >= 0  and 
+            int(event["DurationInSeconds"]) < 9):
+            confirm_scheduled_event(event["EventId"])
+            
+        # Events that may be impactful (eg. Reboot or redeploy) may need custom 
+        # handling for your application
+        else: 
+            #TODO Custom handling for impactful events
+            log(event)
+    print("Processed events from document: " + str(found_document_incarnation))
+    return found_document_incarnation
 
 def main():
-    data = get_scheduled_events()
-    handle_scheduled_events(data)
+    # This will track the last set of events seen 
+    last_document_incarnation = "-1"
+
+    input_text = "\
+        Press 1 to poll for new events \n\
+        Press 2 to exit \n "
+    program_exit = False 
 
+    while program_exit == False:
+        user_input = input(input_text)    
+        if (user_input == "1"):                        
+            last_document_incarnation = advanced_sample(last_document_incarnation)
+        elif (user_input == "2"):
+            program_exit = True       
 
 if __name__ == '__main__':
     main()
 ```
 
 ## Next steps 
 - Review the Scheduled Events code samples in the [Azure Instance Metadata Scheduled Events GitHub repository](https://github.com/Azure-Samples/virtual-machines-scheduled-events-discover-endpoint-for-non-vnet-vm).
+- Review the Node.js Scheduled Events code samples in [Azure Samples GitHub repository](https://github.com/Azure/vm-scheduled-events).
 - Read more about the APIs that are available in the [Instance Metadata Service](instance-metadata-service.md).
 - Learn about [planned maintenance for Windows virtual machines in Azure](../maintenance-and-updates.md?bc=/azure/virtual-machines/windows/breadcrumb/toc.json&toc=/azure/virtual-machines/windows/toc.json).
 - Learn how to [monitor scheduled events for your VMs through Log Analytics](./scheduled-event-service.md).
+- Learn how to log scheduled events using Azure Event Hub in the [Azure Samples GitHub repository](https://github.com/Azure-Samples/virtual-machines-python-scheduled-events-central-logging).
