kubernetes 从volume中理解configmap

Question

I am playing around with kubernetes config map and wanted to understand how the volume mounts work

I have a json config file called client_config.json that is

{
  "name": "place",
  "animal": "thing",
  "age": 10
}

I created a config map using the command

kubectl create configmap client-config --from-file=client_config.json

I then mount it to a volume onto my deployment as

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: go-web-app
spec:
  replicas: 2
  selector:
    matchLabels:
      name: go-web-app
  template:
    metadata:
      labels:
        name: go-web-app
    spec:
      containers:
        - name: application
          image: my/repo
          ports:
            - containerPort: 3000
          volumeMounts:
            - name: config
              mountPath: /client-config
              readOnly: true
      volumes:
        - name: config
          configMap:
            name: client-config

In my go application I am able to read the config using

func config(w http.ResponseWriter, r *http.Request) {
    b, err := ioutil.ReadFile(filepath.Clean("./client_config.json"))
    if err != nil {
        fmt.Fprintf(w, fmt.Sprintf("error reading config: %s", err))
    } else {
        fmt.Fprintf(w, fmt.Sprintf("config value is : %s", string(b)))
    }

}

My question is that configmap was mounted to a mount path as

mountPath: /client-config

But I am reading it from the code as

b, err := ioutil.ReadFile(filepath.Clean("./client_config.json"))

What is the use of the mount path /client-config when I do not need to even reference it when I am reading the configmap as a file?

Answer 1

Thanks to David 's comment I was able to resolve the issue.

Issue was I was including the client_config.json file along with the image, because of which my code was able to reference it via the path ./client_config.json

After I rebuilt the image without client_config.json in it I got the error

error reading config: open client_config.json: no such file or directory

I then corrected my code to use the mount path and I am now able to read the configmap as a file from the volume

b, err := ioutil.ReadFile(filepath.Clean("/client-config/client_config.json"))
if err != nil {
    fmt.Fprintf(w, fmt.Sprintf("error reading config: %s", err))
} else {
    fmt.Fprintf(w, fmt.Sprintf("config value is : %s", string(b)))
}

Answer 2

./client_config.json is a relative file path. Most probably, your app's current working directory is /client-config . Your actual file is located at /client-config/client_config.json .