FileSystemScheduleMonitor crash on read-only file system

[belcher-rok]

Problem

On non-Windows machines, the FileSystemScheduleMonitor class persists scheduled timers to "$HOME/data/webjobs\timers" (note the backslash). This causes problems when using a read-only filesystem on non-Windows machines, such as a Linux container.

Steps to reproduce

1. Create a WebJobs application
2. Add a package reference to Microsoft.Azure.WebJobs.Extensions v5.0.
3. Call AddTimers() on the WebJobs Host Builder.
4. Build and run to verify it works correctly.
5. Copy the following text into a compose.yaml file:

services:
  test-app:
    build:
      context: "."
      dockerfile_inline: |
        FROM mcr.microsoft.com/dotnet/sdk:9.0 as build
        WORKDIR /src
        COPY . .
        RUN dotnet build -c Release
        RUN dotnet publish -o ./app
        FROM mcr.microsoft.com/dotnet/runtime:9.0
        WORKDIR /app
        COPY --from=build /src/app .
        USER app
        ENTRYPOINT ["dotnet", "test.dll"]
    # use a read-only OS
    read_only: true 
    volumes:
      # make tmp folder writable
      - target: /tmp
        type: tmpfs
        tmpfs:
          size: 100Mb
      # make "$HOME/data/webjobs" folder writable
      - target: /home/app/data/webjobs
        type: tmpfs
        tmpfs:
          size: 50Mb

6. Run docker compose up --build.

   If I got the Compose syntax correct, the app should build, start, then crash with the error: Unexpected fatal in startup: Read-only file system : '/home/app/data/webjobs\timers'.

7. Okay, due to the errant backslash, the timers folder is actually named 'webjobs\timers'. So, let's change the volume mount to /home/app/data and try again: docker compose up --wait && docker compose logs --follow. This time it appears to work, but not so fast... Let's restart the container: docker compose restart && docker compose logs --follow. Now it is crashing on start-up again.

Workarounds

There are two known workarounds:

1. Change the volume mount to $HOME/data/webjobs\timers. This allows my app to work, but as soon as this bug is fixed, my container will fail on startup since $HOME/data/webjobs/timers will be read-only.
2. Disable read-only filesystem, assuming your company policy allows it (mine does not).

Expected

1. WebJob Timers should work on read-only filesystem.
2. The WebJobs "data" folder should be configurable, not hard coded (although I suppose someone could argue that it is "configurable" via the HOME variable. I don't know enough about Linux to know if that is a wise solution or not).

Version Info

• .NET SDK 9.0.200
• Microsoft.Azure.WebJobs 3.0.41
• Microsoft.Azure.WebJobs.Extensions 5.0
• TargetFramework: net9.0