kubernetes add local files to pod

If you just want to pass a file or directory to a Pod for the purpose of reading configuration values (which I assume from your choice of volume mount config-volume) and has no need to update the file/directory, then you can just put the file(s) in a ConfigMap like below:

apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-router-config
data:
  nginx.conf: |
    worker_processes 2;
    user nginx;
    events {
        worker_connections  1024;
    }

    http {
        include       mime.types;
        charset       utf-8;
        client_max_body_size 8M;

        server {
            server_name _;
            listen 80 default_server;

            location / {
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-Host $host;
                proxy_set_header X-Forwarded-Proto https;
                proxy_pass http://drupal:80/ ;
                proxy_redirect default;
            }

            location /api/ {
                proxy_pass http://api-gateway:8080/ ;
                proxy_redirect default;
            }
        }
    }  

Or you can have the file content imported from where you run the kubectl command and execute (assuming the file name is nginx.conf):

kubectl create configmap nginx-router-config --from-file=nginx.conf

Then, you can mount the file(s) by adding volumes and volumeMount to the Deployment spec:

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: nginx-router
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80
        volumeMounts:
        - name: nginx-router-config
          mountPath: /etc/nginx/nginx.conf
          subPath: nginx.conf
      volumes:
        - name: nginx-router-config
          configMap:
            name: nginx-router-config
            items:
              - key: nginx.conf
                path: nginx.conf

If you actually want to have read-write access to the file(s) then you can use PersistentVolume and PersistentVolumeClaim as suggested by the other answer, although I will not recommend using hostPath if you have more than one worker node.

if you want to add local file from host then following will work

apiVersion: v1
kind: Pod
metadata:
  name: test-webserver
spec:
  containers:
  - name: test-webserver
    image: k8s.gcr.io/test-webserver:latest
    volumeMounts:
    - mountPath: /var/local/aaa/1.txt
      name: myfile
      readOnly: true
  volumes:
  - name: myfile
    hostPath:
      path: /var/local/aaa/1.txt
      type: File

you can do it like this

kind: PersistentVolume
apiVersion: v1
metadata:
  name: config-volume-pv
  labels:
    type: local
spec:
  storageClassName: generic
  capacity:
    storage: 100Mi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/path/to/volume"

---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  creationTimestamp: null
  name: config-volume-pvc
spec:
  storageClassName: generic
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 100Mi
status: {}

---
kind: Service
metadata:
  name: vol-test
  labels:
    app: vol-test
spec:
  type: NodePort
  ports:
    - port: 8200
      nodePort: 30008
  selector:
    app: vol-test

---

apiVersion: apps/v1
kind: Deployment
metadata:
  name: vol-test
spec:
  replicas: 1
  selector:
    matchLabels:
      app: vol-test
  template:
    metadata:
      labels:
        app: vol-test
    spec:
      containers:
        - name: vol-test
          image: nginx
          imagePullPolicy: "IfNotPresent"
          volumeMounts:
          - mountPath: /blah/
            name: ng-data
          ports:
            - containerPort: 8200
      volumes:
      - name: ng-data
        persistentVolumeClaim:
          claimName: config-volume-pvc

workload resource like Service, Deployment etc cant mount volumes to folders that are not present within the pod.

Make sure that you have the folder created in the pod before its mounted. Best way is to have a this defined in the docker file if you are creating your own images or else have a script that creates the required folders at the start of the pod.