Azure Function Apps scalability metrics and terminology for Premium tier

Question

I'm trying to better understand the scalability behavior of my Premium function apps but I'm confused regarding terminology. Specifically I was trying to understand how many "servers" and how many "containers" of my app are running, but I can't be sure what these metrics precisely are:

• AppRoleInstance
• HostInstanceId
• ProcessId

At first I thought a "Host" would be close to a VM and an "Instance" would be close to a container, but according to what I see that might be actually the other way around. And the dcount of ProcessId varies between 1 & 2 on a Always Available Function App with minimum 3 so I can't really understand what this process-id is. The AppRoleInstance and the HostInstanceId are matching most of the time except for some "host" spikes. For reference the query I'm using is similar to this:

AppTraces
| where AppRoleName = <function-app-name>
| summarize
    dcount(tostring(AppRoleInstance)),
    dcount(tostring(Properties.HostInstanceId)),
    dcount(tostring(Properties.ProcessId))
  by bin(TimeGenerated, 1h)
| render timechart

Answer 1

And the dcount of ProcessId varies between 1 & 2 on a Always Available Function App with minimum 3 so I can't really understand what this process-id is.

Process Id gets assigned in Kudu site as soon as host is initiated for a function.

• You can verify the same by navigating to Advanced Tools.

• w3wp.exe handler gets activated when the function gets triggered and it stays active as long as that job host is active.

• If the function app is idle for 20mins then the Job host stops and you will no longer see w3wp.exe.

• When you will trigger the function or any activity is detected then a new host will be initialized with a new process id.

• AppRoleInstance represents the number of Function App instances running at a time and each instance acts as a container which is running in a server.
• HostInstanceId represents number of servers hosting for your function app.
• Process Id represents the number of processes running in a container. In a Function App, each container can have a single process but if you are using Always On hosting plan then you can see multiple processes running.