Kubernetes multi-tier container application

Question

I have two Docker containers running Flask and redis each that communicate well when linked using Docker container linking.

I am trying to deploy the same on Kubernetes using services and pods but, it's not working. I am learning Kubernetes so I must be doing something wrong here.

Below are the Docker commands that work well:

$ docker run -d --name=redis -v /opt/redis:/redis -p 6379 redis_image redis-server
$ docker run -d -p 5000:5000 --link redis:redis --name flask flask_image

The kubernetes pod and services files are as below:

pod-redis.yaml

apiVersion: v1
kind: Pod
metadata:
  name: redis
  labels:
    name: redis
    app: redis
spec:
  containers:
  - name: redis
    image: dharmit/redis
    command:
    - "redis-server"
  volumeMounts:
  - mountPath: /redis
    name: redis-store
  volumes:
  - name: redis-store
    hostPath:
      path: /opt/redis

service-redis.yaml

apiVersion: v1
kind: Service
metadata:
  name: redis
  labels:
    name: redis
spec:
  ports:
  - port: 6379
    targetPort: 6379
  selector:
    app: redis

pod-flask.yaml

apiVersion: v1
kind: Pod
metadata:
  name: flask
  labels:
    name: flask
    app: flask
spec:
  containers:
  - name: flask
    image: dharmit/flask 
    ports:
    - containerPort: 5000

service-flask.yaml

apiVersion: v1
kind: Service
metadata:
  name: flask
  labels:
    name: flask
spec:
  ports: 
  - port: 5000
  selector:
    app: flask

When I do kubectl create -f /path/to/dir/ all services and pods start up fine and get listed by kubectl commands. But when I try to access the port 5000, Flask app complains that it cannot communicate with redis container. Below are the service related outputs:

flask service

Name:           flask
Namespace:      default
Labels:         name=flask
Selector:       app=flask
Type:           ClusterIP
IP:         10.254.155.179
Port:           <unnamed>   5000/TCP
Endpoints:      172.17.0.2:5000
Session Affinity:   None
No events.

redis service

Name:           redis
Namespace:      default
Labels:         name=redis
Selector:       app=redis
Type:           ClusterIP
IP:         10.254.153.217
Port:           <unnamed>   6379/TCP
Endpoints:      172.17.0.1:6379
Session Affinity:   None
No events.

And the output of curl command:

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/usr/lib/python2.7/site-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/usr/lib/python2.7/site-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/app/app/views.py", line 9, in index
    if r.get("count") == None:
  File "/usr/lib/python2.7/site-packages/redis/client.py", line 863, in get
    return self.execute_command('GET', name)
  File "/usr/lib/python2.7/site-packages/redis/client.py", line 570, in execute_command
    connection.send_command(*args)
  File "/usr/lib/python2.7/site-packages/redis/connection.py", line 556, in send_command
    self.send_packed_command(self.pack_command(*args))
  File "/usr/lib/python2.7/site-packages/redis/connection.py", line 532, in send_packed_command
    self.connect()
  File "/usr/lib/python2.7/site-packages/redis/connection.py", line 436, in connect
    raise ConnectionError(self._error_message(e))
ConnectionError: Error -2 connecting to redis:6379. Name or service not known.

What am I doing wrong here?

Do you add volume in flask container. seems like you added in docker — Shahriar
@AerofoilKite No I haven't mentioned volumes in flask container. Do I need to? — Dharmit
Are you actually running the DNS server? You don't mention what environment you're using. — Tim Hockin

Shahriar Shahriar · Accepted Answer · 2015-10-25T11:18:49

You need to add containerPort in your pod-redis.yaml

- name: redis
  image: dharmit/redis
  command:
    - "redis-server"
  ports: 
    - containerPort: 6379
      hostPort: 6379

Kubernetes multi-tier container application

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