SFTP server is not accessible when deployed to Kubernetes (GKE)

Question

The SFTP server is inaccessible when exposed using a NodePort service and a Kubernetes Ingress. However, if the same Deployment is exposed via a LoadBalancer Service, it works fine.

Below is the deployment file for SFTP in Google Kubernetes Engine using the atmoz/sftp Dockerfile.

kind: Deployment
apiVersion: extensions/v1beta1
metadata:
  name: sftp
  labels:
    environment: production
    app: sftp
spec:
  replicas: 1
  minReadySeconds: 10
  template:
    metadata:
      labels:
        environment: production
        app: sftp
      annotations:
        container.apparmor.security.beta.kubernetes.io/sftp: runtime/default
    spec:
      containers:
        - name: sftp
          image: atmoz/sftp:alpine
          imagePullPolicy: Always
          args: ["user:pass:1001:100:upload"]
          ports:
            - containerPort: 22
          securityContext:
            capabilities:
              add: ["SYS_ADMIN"]
          resources: {}

If I expose this Deployment normally using a Kubernetes Service of type LoadBalancer as shown below, this Service obtains an external IP, which I can simply use in the command sftp xxx.xx.xx.xxx to access it using the pass password.

apiVersion: v1
kind: Service
metadata:
  labels:
    environment: production
  name: sftp-service
spec:
  type: LoadBalancer
  ports:
  - name: sftp-port
    port: 22
    protocol: TCP
    targetPort: 22
  selector:
    app: sftp

However, when I try to expose the same deployment using Ingress it does not work.

After assigning an external IP to the Ingress (acknowledging that it takes a few minutes to fully set up), xxx.xx.xx.xxx/sample starts working, but sftp -P 80 xxx.xx.xx.xxx does not.

# First I create a NodePort service to expose the deployment internally

---
apiVersion: v1
kind: Service
metadata:
  labels:
    environment: production
  name: sftp-service
spec:
  type: NodePort
  ports:
  - name: sftp-port
    port: 22
    protocol: TCP
    targetPort: 22
    nodePort: 30063
  selector:
    app: sftp

# Ingress service has SFTP service as its default backend
---
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: basic-ingress-2
spec:
  backend:
    serviceName: sftp-service
    servicePort: 22
  rules:
  - http:
      paths:
      # "http-service-sample" is a service exposing a simple hello-word app deployment
      - path: /sample
        backend:
          serviceName: http-service-sample
          servicePort: 80

Below is the error I get from the server:

ssh_exchange_identification: Connection closed by remote host
Connection closed

What am I doing wrong in the above setup? Why is the LoadBalancer service able to grant access to the SFTP service, while the Ingress fails?

Answer 1

That's currently not fully supported to route in Kubernetes Ingress any other traffic than HTTP/HTTPS protocols (see docs).

You can try to make some workaround as described there: Kubernetes: Routing non HTTP Request via Ingress to Container