Kubernetes - Reload your ASP.NET Core configuration when a configmap changes–DOTNET_USE_POLLING_FILE_WATCHER

In a previous post I showed how you can use ConfigMaps in Kubernetes. This allows you to update for example our appsettings.json without the need to upload a new container image and update our pods.

Sounds great! However there is one challenge with this approach. In Kubernetes a config map is mounted as a symlink, and .NET is not able to pick up changes applied to the original file by just knowing about the symlink. I mentioned some workarounds but an out-of-the-box solution was not available at that time.

DOTNET_USE_POLLING_FILE_WATCHER

Now a solution to the problem above is available through the DOTNET_USE_POLLING_FILE_WATCHER environment variable. By setting this value to “true” or “1”, we can instruct .NET to not use the default FileSystemWatcher but using a polling mechanism instead.

	apiVersion: apps/v1
	kind: Deployment
	metadata:
	name: example-api-deployment
	spec:
	selector:
	matchLabels:
	app: example-api
	replicas: 2
	strategy:
	type: RollingUpdate
	rollingUpdate:
	maxUnavailable: 1
	template:
	metadata:
	labels:
	app: example-api
	spec:
	containers:
	- name: example-api
	image: my.azurecr.io/example:latest
	env:
	- name: DOTNET_USE_POLLING_FILE_WATCHER
	value: "true"
	ports:
	- containerPort: 80
	volumeMounts:
	- name: appsettings-volume
	mountPath: /app/appsettings.json
	subPath: appsettings.json
	volumes:
	- name: appsettings-volume
	configMap:
	name: example-configmap

view raw deployment.yaml hosted with ❤ by GitHub

More information: dotnet watch