kubernetes config deployment removing existing files

Question

I want to update the existing file settings.ini in container at the time of helm deployment without harming existing data in container.

Here are my helm files -

config.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Values.metadata.name }}-config
data:
  settings.ini: |
    [server]
    hostname = "localhost"
    hot_deployment = false
    # offset  = 10

    [user_store]
    type = "read_only_ldap"

deployment part from Deployment.yaml

containers:
  - name: {{ .Chart.Name }}
    securityContext:
      {{- toYaml .Values.securityContext | nindent 12 }}
    image: "{{ .Values.image.repository }}:{{ .Values.image.tag | default .Chart.AppVersion }}"
    imagePullPolicy: {{ .Values.image.pullPolicy }}
    ports:
      - name: http
        containerPort: 80
        protocol: TCP
    volumeMounts:
    - name: config-volume
      mountPath: /home/bin/conf/
      subPath: settings.ini
volumes:
  - name: config-volume
    configMap:
      name: {{ .Values.metadata.name }}-config

I can see it creating config map successfully but when I check logs in the cluster it complains about missing files

How can I resolve this issue?

Also is there any efficient way to achieve this, if I just want to update some of the configurations for my settings.ini file with different values in different env?

Answer 1

In the recent versions of k8s Mounted ConfigMaps are Updated Automatically:

When a ConfigMap currently consumed in a volume is updated, projected keys are eventually updated as well. The kubelet checks whether the mounted ConfigMap is fresh on every periodic sync.

A container using a subPath volume mount may not receive the updates.

Possible solution:

Use two containers:

• Main Container: Will run your application, listen to a specific port/endpoint_path for HTTP requests. On receiving the request, your application should reload the configurations. Since the subPath method is avoided, you may store the configMap to some other directory, later move/update to the desired directory while reloading configurations.
• SideCar: Will run file change watcher like configmap-reload, on changes of file it will send an HTTP request to the main container.

Sample:

containers:
  - name: main-container
    image: application:v1.0.0
    ports:
      - name: http
        containerPort: 80
        protocol: TCP
    volumeMounts:
    - name: config-volume
      mountPath: /some/path

  - name: side-car
    image: jimmidyson/configmap-reload:latest
    args:
    - "-volume-dir=/some/path"
    - "-webhook-url=localhost:80/reload-config"
    volumeMounts:
    - name: config-volume
      mountPath: /some/path

volumes:
  - name: config-volume
    configMap:
      name: {{ .Values.metadata.name }}-config