Do Azure Function from Same App Service Run in Same Instance

Question

I have a scenario where one of my Class has a static member whose value I can set from a Function App. Suppose another Function App belonging to same App Service Plan also uses this same class and also sets/relies on the value of the static member. Now, if the two function apps never run simultaneously, we have no issue. Also, if they don't run under same instance, then we also have no issue as each running instance will have their own definition of the class.

My question is, do each Function App from same App Service run on different instance?

I understand redesigning will eliminate any possible issues, but I am just curious on the interaction between Function Apps in same App Service.

Answer 1

I think it will be better for you to understand the process boundaries.

You have an Azure Function App (FuncApp1.azurewebsites.net) that may have one or more functions hosted on an App Service Plan. You're mentioning that you have another Azure Function App (FuncApp2.azurewebsites.net) with one or more of it's own set of functions hosted on the same App Service Plan. Is this correct?

FuncApp1 will have it's own process id, memory/cpu consumption, and threads on some machine in the cloud and the same for FuncApp2. The static member basically exists independently in two separate programs. In the case where your function app may scale out, each new instance will most likely have it's own process id, etc.

So NO your function apps will not step on each other. Your only concern should be if the static member is thread safe within the same process id. In what scenario are you relying on a static member that may be altered per request? Some incrementing ID?