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By: Sandeep Dinesh - July 29, 2015

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In a recent post, I talked about running a MEAN stack with Docker Containers.

Manually deploying Containers is all fine and dandy, but is rather fragile and clumsy. What happens if the app crashes? How can the app be updated? Rolled back?

Thankfully, there is a system we can use to manage our containers in a cluster environment called Kubernetes. Even better, Google has a managed version of Kubernetes called Google Container Engine so you can get up and running in minutes.

The Basics of Using Kubernetes

Before we jump in and start kube’ing it up, it’s important to understand some of the fundamentals of Kubernetes.

Step 1: Creating the Container

In my previous post, I used off-the-shelf containers to keep things simple.

I had a stock MongoDB container and a stock Node.js container. The Mongo container ran fine without any modification. However, I had to manually enter the Node container to pull and run the code. Obviously this isn’t ideal in Kubernetes land, as you aren’t supposed to log into your servers!

Instead, you have to build a custom container that has the code already inside it and runs automatically.

To do this, you need to use more Docker. Make sure you have the latest version installed for the rest of this tutorial.

Getting the code:

Before starting, let’s get some code to run. You can follow along on your personal machine or a Linux VM in the cloud. I recommend using Linux or a Linux VM; running Docker on Mac and Windows is outside the scope of this tutorial.

$ git clone https://github.com/ijason/NodeJS-Sample-App.git app
$ mv app/EmployeeDB/* app/
$ sed -i -- 's/localhost/mongo/g' ./app/app.js

This is the same sample app we ran before. The second line just moves everything from the EmployeeDB subfolder up into the app folder so it’s easier to access. The third line, once again, replaces the hardcoded localhost with the mongo proxy.

Building the Docker image:

First, you need a Dockerfile. This is basically the list of instructions Docker uses to build a container image.

Here is the Dockerfile for the web server:

FROM node:4.4

RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app
COPY ./app/ ./
RUN npm install

CMD ["node", "app.js"]

A Dockerfile is pretty self-explanatory, and this one is dead simple.

First, it uses the official Node.js LTS image as the base image.

Then, it creates a folder to store the code, cds into that directory, copies the code in, and installs the dependencies with npm.

Finally, it specifies the command Docker should run when the container starts, which is to start the app.

Step 2: Building our Container

Right now, the directory should look like this:

$ ls

Dockerfile app

Let’s build.

$ docker build -t myapp .

This will build a new Docker image for your app. This might take a few minutes as it is downloading and building everything.

After that is done, test it out:

$ docker run myapp

At this point, you should have a server running on http://localhost:3000 (or wherever Docker tells you). The website will error out as there is no database running, but we know it works!

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Step 3: Pushing our Container

Now you have a custom Docker image, you have to actually access it from the cloud.

As we are going to be using the image with Google Container Engine, the best place to push the image is the Google Container Registry. The Container Registry is built on top of Google Cloud Storage, so you get the advantage of scalable storage and very fast access from Container Engine.

First, make sure you have the latest version of the Google Cloud SDK installed.

Windows users click here.

For Linux/Mac:

$ curl https://sdk.cloud.google.com | bash

Then, make sure you log in and update.

$ gcloud auth login
$ gcloud components update

You’re ready to push your container live, but you’ll need a destination. Create a Project in the Google Cloud Platform Console, and leave it blank. Use the Project ID below, and push your project live.

$ docker tag myapp gcr.io/<YOUR-PROJECT-ID>/myapp
$ gcloud docker push gcr.io/<YOUR-PROJECT-ID>/myapp

After some time, it will finish. You can check the console to see the container has been pushed up.

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Step 4: Creating the Cluster

So now you have the custom container, let’s create a cluster to run it.

Currently, a cluster can be as small as one machine to as big as 100 machines. You can pick any machine type you want, so you can have a cluster of a single f1-micro instance, 100 n1-standard-32 instances (3,200 cores!), and anything in between.

For this tutorial I’m going to use the following:

There are two ways to create this cluster. Take your pick.

Command Line:

$ gcloud beta container \
 --project "<YOUR-PROJECT-ID>" \
 clusters create "mean-cluster" \
 --zone "us-central1-f" \
 --machine-type "n1-standard-1" \
 --num-nodes "2" \
 --network "default"

GUI:

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After a few minutes, you should see this in the console.

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Step 5: Creating the Database Service

Three things need to be created:

  1. Persistent Disk to store the data (pods are ephemeral, so we shouldn’t save data locally)
  2. Deployment running MongoDB
  3. Service mapping to that Deployment

To create the disk, run this:

$ gcloud compute disks create \
 --project "<YOUR-PROJECT-ID>" \
 --zone "us-central1-f" \
 --size 200GB \
 mongo-disk

Pick the same zone as your cluster and an appropriate disk size for your application.

Now, we need to create a Deployment that will run the database. I’m using a Deployment and not a Pod, because if a standalone Pod dies, it won’t restart automatically.

db-deployment.yml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: mongo-deployment
spec:
  replicas: 1
  template:
    metadata:
      labels:
        name: mongo
    spec:
      containers:
      - image: mongo
        name: mongo
        ports:
        - name: mongo
          containerPort: 27017
          hostPort: 27017
        volumeMounts:
          - name: mongo-persistent-storage
            mountPath: /data/db
      volumes:
        - name: mongo-persistent-storage
          gcePersistentDisk:
            pdName: mongo-disk
            fsType: ext4

We call the deployment mongo-deployment, specify one replica, and open the appropriate ports. The image is mongo, which is the off the shelf MongoDB image.

The volumes section creates the volume for Kubernetes to use. There is a Google Container Engine-specific gcePersistentDisk section that maps the disk we made into a Kubernetes volume, and we mount the volume into the /data/db directory (as described in the MongoDB Docker documentation)

Now we have the Deployment, let’s create the Service:

db-service.yml

apiVersion: v1
kind: Service
metadata:
 labels:
   name: mongo
 name: mongo
spec:
 ports:
   - port: 27017
     targetPort: 27017
 selector:
   name: mongo

Again, pretty simple stuff. We “select” the mongo Deployment to be served, open up the ports, and call the service mongo.

This is just like the “link” command line option we used with Docker in my previous post. Instead of connecting to localhost, we connect to mongo, and Kubernetes redirects traffic to the mongo service!

At this point, the local directory looks like this:

$ ls

Dockerfile
app
db-deployment.yml
db-service.yml

Step 6: Running the Database

First, let’s “log in” to the cluster

$ gcloud container clusters get-credentials mean-cluster

Now create the Deployment.

$ kubectl create -f db-deployment.yml

And the Service.

$ kubectl create -f db-service.yml

kubectl is the Kubernetes command line tool (automatically installed with the Google Cloud SDK). We are just creating the resources specified in the files.

At this point, the database is spinning up! You can check progress with the following command:

$ kubectl get pods

Once you see the mongo pod in running status, we are good to go!

$ kubectl get pods

NAME                    READY  REASON   RESTARTS AGE
mongo-deployment-xxxx   1/1    Running  0        3m

Step 7: Creating the Web Server

Now the database is running, let’s start the web server.

We need two things:

  1. Deployment to spin up and down web server pods
  2. Service to expose our website to the interwebs

Let’s look at the Deployment configuration:

web-deployment.yml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: web-deployment
spec:
  replicas: 2
  template:
    metadata:
      labels:
        name: web
    spec:
      containers:
      - image: gcr.io/<YOUR-PROJECT-ID>/myapp
        name: web
        ports:
        - name: http-server
          containerPort: 3000

Here, we create a deployment called web-deployment, and we tell it to create two replicas. Replicas of what you ask? You may notice the template section looks just like a Pod configuration, and that’s because it is. We are creating a Pod with our custom Node.js container and exposing port 3000.

Now for the Service

web-service.yml

apiVersion: v1
kind: Service
metadata:
 name: web
 labels:
   name: web
spec:
 type: LoadBalancer
 ports:
   - port: 80
     targetPort: 3000
     protocol: TCP
 selector:
   name: web

Notice two things here:

  1. The type is LoadBalancer. This is a cool feature that will make Google Cloud Platform create an external network load balancer automatically for this service!
  2. We map external port 80 to the internal port 3000, so we can serve HTTP traffic without messing with Firewalls.

At this point, the local directory looks like this

$ ls

Dockerfile 
app
db-deployment.yml
db-service.yml
web-service.yml
web-deployment.yml

Step 8: Running the Web Server

Create the Deployment.

$ kubectl create -f web-deployment.yml

And the Service.

$ kubectl create -f web-service.yml

And check the status.

$ kubectl get pods

Once you see the web pods in running status, we are good to go!

$ kubectl get pods

NAME                   READY     REASON    RESTARTS   AGE
mongo-deployment-xxxx  1/1       Running   0          4m
web-deployment-xxxx    1/1       Running   0          1m
web-deployment-xxxx    1/1       Running   0          1m

Step 9: Accessing the App

At this point, everything is up and running. The architecture looks something like this:

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By default, port 80 should be open on the load balancer. In order to find the IP address of our app, run this command:

$ gcloud compute forwarding-rules list

NAME     REGION        IP_ADDRESS       IP_PROTOCOL TARGET
abcdef   us-central1   104.197.XXX.XXX  TCP         us-xxxx

If you go to the IP address listed, you should see the app up and running!

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And the Database works!

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Final Thoughts

By using Container Engine and Kubernetes, we have a very robust, container based MEAN stack running in production.

In another post, I cover how to setup a MongoDB replica set. This is very important for running in production.

Hopefully I can do some more posts about advanced Kubernetes topics such as changing the cluster size and number of Node.js web server replicas, using different environments (dev, staging, prod) on the same cluster, and doing rolling updates.

Thanks to Mark Mandel, Aja Hammerly, and Jack Wilber. Some rights reserved by the author.

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