Nov 21 2019 06:32 AM
Nov 21 2019 06:32 AM
I am trying to write a KQL query to catch if any single heartbeat missed.
Like we could see in my below screenshot, this server is sending heartbeat after every minute interval.
And now there is gap in heartbeat when i stopped the scx service, so now i want to track if any single heartbeat will miss then i should have an alert notification.
Nov 22 2019 09:45 AMSolution
personally I prefer the example query of
// Availability rate // Calculate the availability rate of each connected computer Heartbeat // bin_at is used to set the time grain to 1 hour, starting exactly 24 hours ago | summarize heartbeatPerHour = count() by bin_at(TimeGenerated, 1h, ago(24h)), Computer | extend availablePerHour = iff(heartbeatPerHour > 0, true, false) | summarize totalAvailableHours = countif(availablePerHour == true) by Computer | extend availabilityRate = totalAvailableHours*100.0/24
Heartbeats are expected to be missed (pauses, glitches, load etc...) and the data will catch-up - so you may get false positives.
You can use a date_diff to compare
Go to Log Analytics and Run Query
Heartbeat | where TimeGenerated >= ago(1h) | where Computer == "hardening-demo" | project Computer, TimeGenerated | order by TimeGenerated desc | project n = TimeGenerated, nminus = prev(TimeGenerated), TimeGenerated, Computer | where isnotempty(nminus) // show time NOW vs time n -1 row | extend second = datetime_diff('second',nminus, n) | where second >= 60
Results for seconds below 60 (mainly 9 and 51 for the demo data) - just remove the last line of the above query to see this
Jan 28 2020 10:46 AM
@Clive Watson Just to add to this conversation, I've come up with a slightly different way of doing this--would love feedback:
let current = now(); let ostype = 'Windows'; let computername = ''; let environment = 'Non-Azure'; let threshold = 600; Heartbeat | where TimeGenerated >= ago(1h) // --for a specific computer: | where Computer contains computername // --for a specific computer group: //| where Computer in (group) // --for a specific OS type: | where OSType contains ostype // --for on-prem or Azure VMs: | where ComputerEnvironment contains environment | project Computer, TimeGenerated, current | order by TimeGenerated desc | project nminus = prev(TimeGenerated), current, Computer | where isnotempty(nminus) | extend ['LastHeartbeat (in seconds)'] = datetime_diff('second', current, nminus) | summarize arg_max(nminus, *) by Computer | where ['LastHeartbeat (in seconds)'] >= threshold | project Computer, QueryTime = current, LastTimeStamp = nminus, ['LastHeartbeat (in seconds)']
Jan 29 2020 10:23 AM
Looks good @Scott Allison , I would just swap contains to has as per best practise https://docs.microsoft.com/en-us/azure/kusto/query/best-practices
Feb 03 2020 04:37 AM
@Clive Watson - here's a perfect example of why the HAS operator isn't useful for many operations:
This query returns the expected results every time:
Heartbeat | where Computer contains 'abc' | distinct Computer
For example, this would return:
When I replace CONTAINS with HAS, I get 0 results. So in 99% of my use cases, HAS doesn't work at all.
Feb 03 2020 05:07 AM
That is the behavior I'd expect
From the docs:
has operator over
contains when looking for full tokens.
has is more performant as it doesn't have to look-up for substrings.
What does that mean in practice:
1. This query example will fail (as its not a substring). Computers named: aks-nodepool1.nnnnnnnnn