How do I mount file as ConfigMap inside DaemonSet? - nginx

Question

I have following nginx config file (named nginx-daemonset.conf) that I want to use inside my Daemonset:
events {
worker_connections 1024;
}
http {
server {
listen 80;
location / {
proxy_pass http://my-nginx;
}
}
}
I created a ConfigMap using following command: kubectl create configmap nginx2.conf --from-file=nginx-daemonset.conf
I have following DaemonSet (nginx-daemonset-deployment.yml) inside which I am trying to mount this ConfigMap - so the previous nginx config file is used:
apiVersion: apps/v1
kind: DaemonSet
metadata:
name: nginx-daemonset
namespace: kube-system
labels:
k8s-app: nginx-daemonset
spec:
selector:
matchLabels:
name: nginx-daemonset
template:
metadata:
labels:
name: nginx-daemonset
spec:
tolerations:
# this toleration is to have the daemonset runnable on master nodes
# remove it if your masters can't run pods
- key: node-role.kubernetes.io/master
effect: NoSchedule
containers:
- name: nginx
image: nginx
resources:
limits:
memory: 200Mi
requests:
cpu: 100m
memory: 200Mi
volumeMounts:
- name: nginx2-conf
mountPath: /etc/nginx/nginx.conf
subPath: nginx.conf
volumes:
- name: nginx2-conf
configMap:
name: nginx2.conf
I deployed this Daemonset using kubectl apply -f nginx-daemonset-deployment.yml but my newly created Pod is crashing with the following error:
Error: failed to start container "nginx": Error response from daemon: OCI runtime create failed: container_linux.go:370: starting container process caused: process_linux.go:459: container init caused: rootfs_linux.go:59: mounting "/var/lib/kubelet/pods/cd9f6f7b-31db-4ab3-bbc0-189e1d392979/volume-subpaths/nginx2-conf/nginx/0" to rootfs at "/var/lib/docker/overlay2/b21ccba23347a445fa40eca943a543c1103d9faeaaa0218f97f8e33bacdd4bb3/merged/etc/nginx/nginx.conf" caused: not a directory: unknown: Are you trying to mount a directory onto a file (or vice-versa)? Check if the specified host path exists and is the expected type
I did another Deployment with different nginx config before and everything worked fine, so the problem is probably somehow related to DaemonSet.
Please, how do I get over this error and mount the config file properly?

Answer 1

first create your config file as a ConfigMap like nginx-conf:
apiVersion: v1
kind: ConfigMap
metadata:
name: nginx-conf
data:
envfile: |
events {
worker_connections 1024;
}
http {
server {
listen 80;
location / {
proxy_pass http://my-nginx;
}
}
}
then create your DaemonSet, volumes, configMap and finial y mount volumeMounts with subPath:
apiVersion: apps/v1
kind: DaemonSet
metadata:
name: nginx
spec:
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx
ports:
- name: http
containerPort: 80
volumeMounts:
- mountPath: /etc/nginx/nginx.conf
subPath: nginx.conf
readOnly: true
name: nginx-vol
volumes:
- name: nginx-vol
configMap:
name: nginx-conf
items:
- key: envfile
path: nginx.conf
note that for file mounting instead of directory mounting you must use "path in configMap" and "subPath in volumeMounts".