Docker quick start for Node developers

Some great discussions at yesterdays Container Summit, but the biggest takeaway is that container technology is fully production ready (and has actually already in production in various companies for years), and fully exploits all the security features provided by Linux.

Node developers, I recommend getting acquainted with container technology now. The following quick start is up-to-date for current versions of Docker (v1.8.1) and Node.js (v4.0.0).

Install Dependencies

For Mac and Windows users, just install Docker Toolbox. It provides what you need to get started, including:

  • Docker Machine - for creating Docker hosts ("machines")
  • Docker Client - for communicating with docker hosts
  • VirtualBox - to create docker hosts in a Linux-based (boot2docker) virtual machine

https://www.docker.com/toolbox

Working with Docker Machine

List Docker machines

$ docker-machine ls
NAME      ACTIVE   DRIVER         STATE     URL                          SWARM
default            virtualbox     Running   tcp://192.168.99.100:2376

Create a new machine

$ docker-machine create --driver virtualbox dev
Creating VirtualBox VM...
Creating SSH key...
Starting VirtualBox VM...
Starting VM...
To see how to connect Docker to this machine, run: docker-machine env dev

Now list machines

$ docker-machine ls
NAME      ACTIVE   DRIVER         STATE     URL                          SWARM
default            virtualbox     Running   tcp://192.168.99.100:2376
dev                virtualbox     Running   tcp://192.168.99.101:2376

Tell the Docker client to use the new machine

$ eval "$(docker-machine env dev)"

This command evaluates the command docker-machine env dev, which results in updating environment variables used by the Docker client to communicate with a machine.

This means that any docker commands you issue will be executed for the docker machine named dev.

Stop a machine

$ docker-machine stop dev

Start a machine

$ docker-machine start dev
Starting VM...
Started machines may have new IP addresses. You may need to re-run the `docker-machine env` command.

Get the machine host IP

$ docker-machine ip dev
192.168.99.101

ssh into the machine

$ docker-machine ssh dev
Boot2Docker version 1.8.1, build master : 7f12e95 - Thu Aug 13 03:24:56 UTC 2015  
Docker version 1.8.1, build d12ea79  
docker@dev:~$  

Create a machine using other provider drivers

https://docs.docker.com/machine/drivers/

DigitalOcean example

Make sure to create a personal access token: https://cloud.digitalocean.com/settings/applications

Add the access token to your environment:

export DIGITALOCEAN_ACCESS_TOKEN='...'

Create a machine

$ docker-machine create --driver digitalocean demo
Creating SSH key...
Creating Digital Ocean droplet...
To see how to connect Docker to this machine, run: docker-machine env demo

List the machine

$ docker-machine ls
NAME      ACTIVE   DRIVER         STATE     URL                          SWARM
default            virtualbox     Running   tcp://192.168.99.100:2376
demo               digitalocean   Running   tcp://107.170.201.137:2376
dev                virtualbox     Running   tcp://192.168.99.102:2376

Set docker client environment to use, just like any other machine

$ eval "$(docker-machine env demo)"

You can also log into your DigitalOcean console and see that the machine has been created.

Remove the machine if you won't need it

$ docker-machine rm demo
Successfully removed demo

Working with Docker

Launch a container to run a command, such as the bash builtin echo command. The container will be created using the BusyBox image (https://registry.hub.docker.com/_/busybox/). BusyBox is just a single executable that defines many common UNIX utilities. It's very small, so it's convenient to use for demonstration purposes. You can substitute ubuntu or another Linux distribution.

$ docker run --rm busybox echo hello
hello

Launch a BusyBox container and run an interactive shell

$ docker run --rm -it busybox sh

Working with Node

Docker Hub Node repository

https://hub.docker.com/_/node/

Pull node image

$ docker pull node

This downloads latest image to your machine.

Run node REPL in a container

$ docker run -it --rm node
> console.log('hello')
hello

This runs the node REPL (read-evaluate-print-loop shell) in a container created from the node image.

It runs a REPL because the container runs the default command as defined by the node image CMD, as defined here:

https://github.com/nodejs/docker-node/blob/c2a8075f1e3155577c071bf1178c59370bb76d1a/4.0/Dockerfile#L26

FROM buildpack-deps:jessie  
...
CMD [ "node" ]  

Run shell command in a node container

Override the default CMD by supplying a command after the name of the node image.

$ docker run -it --rm node node -v
v4.0.0

$ docker run -it --rm node npm -v
2.14.2

Run bash in a container

This will put us into a bash shell in the container

$ docker run -it --rm node bash
root@d72e494e756a:/#

In the bash shell in the node container

# node -v
v4.0.0

# npm -v
2.14.2

Create a simple node app

In a new directory...

Create a package.json file

{
  "name": "simple-docker-node-demo",
  "version": "1.0.0",
  "scripts": {
    "start": "node app.js"
  }
}

Create app.js

console.log('hello world!');

Create a Dockerfile

FROM node:onbuild  

Build an image:

$ docker build -t demo-app .
Sending build context to Docker daemon 4.096 kB  
Step 0 : FROM node:onbuild  
onbuild: Pulling from library/node  
843e2bded498: Already exists  
8c00acfb0175: Already exists  
...
# Executing 3 build triggers
Trigger 0, COPY package.json /usr/src/app/  
Step 0 : COPY package.json /usr/src/app/  
Trigger 1, RUN npm install  
Step 0 : RUN npm install  
 ---> Running in 85dc900dbab9
npm ...  
npm info ok  
Trigger 2, COPY . /usr/src/app  
Step 0 : COPY . /usr/src/app  
 ---> e90767b20603
...
Successfully built e90767b20603  

Docker created an image based on the Dockerfile in the current directory and named it demo-app-1. As part of creating the image, it ran instructions triggered from the 'onbuild' base image that we specified in our Dockerfile that included copying the contents of the current directory to /usr/src/app/ and running npm install.

You can see what the instructions look like here:

https://github.com/nodejs/docker-node/blob/e763a1065077c580aab4d73945597c0b160b4ee2/4.0/onbuild/Dockerfile

The triggers are the ONBUILD statements. These will be run when the image is built that referenced this Dockerfile in its FROM statement.

FROM node:4.0.0

RUN mkdir -p /usr/src/app  
WORKDIR /usr/src/app

ONBUILD COPY package.json /usr/src/app/  
ONBUILD RUN npm install  
ONBUILD COPY . /usr/src/app

CMD [ "npm", "start" ]  

Run the demo app in a container

$ docker run --rm demo-app-1    
npm info it worked if it ends with ok
npm info using npm@2.14.2
npm info using node@v4.0.0
npm info prestart simple-docker-node-demo@1.0.0
npm info start simple-docker-node-demo@1.0.0

> simple-docker-node-demo@1.0.0 start /usr/src/app
> node app.js

hello world
npm info poststart simple-docker-node-demo@1.0.0
npm info ok

The node app is trivial, but the mechanics of how this works is the same for more complicated examples. One thing you will probably want to do is export a port for accessing your node application, which we cover in the next section.

Pushing your image

Save your image for spinning up your app in a node container to Docker repository. You can use Docker Hub.

You will need to create an account on Docker Hub, then login from the command line:

$ docker login

Only official images (such as node) can have simple names. To push your own image, you will need to change the name of the image. Instead of demo-app, you will need to create the image using your login name. Mine is 'subfuzion' so my docker build and docker push commands would look like this:

$ docker build -t subfuzion/demo-app .

Or when you build, give it a tag:

$ docker build -t subfuzion/demo-app:1.0 .

Or if you forget, tag it after:

$ docker tag <image-id> subfuzion:/demo-app:v1

Then push the image to Docker Hub

$ docker push subfuzion/demo-app

Create Express API app and expose a port

Modify the demo to make it an express app. Install express:

$ npm install --save express

Update app.js to start an express server

const app = require('express')();  
const port = process.env.PORT || 3000;

app.use('/', function(req, res) {  
 res.json({ message: 'hello world' });
});

app.listen(port);  
console.log('listening on port ' + port);  

And update Dockerfile

FROM node:onbuild  
expose 3000  

Rebuild the image

$ docker build -t demo-app:v2 .

Now we can run it, but we want to map port 3000 inside the container to a port we can access from our system. We'll pick port 49100:

$ docker run --rm -t -p 49100:3000 demo-app:v2

This won't be an interactive session, so no need for -i, but the -t allows us to send signals from our client, like CTRL-C. As usual, --rm will remove the container for us when it is stopped.

Now we can access the app via port 49100, which will be mapped to port 3000 in the container.

If you're using Docker on a Mac, the port is actually mapped to the Docker host virtual machine. To determine the IP address, enter this at the command line:

$ docker-machine ip dev
192.168.99.102

You should be able to test http://192.168.99.102:49100/ in your browser.

The app looks for the environment variable PORT to be set, otherwise it defaults to 3000. We could specify an alternate port via the environment from the command line like this:

$ docker run --rm -t -p 49100:8080 -e "PORT=8080" demo-app

You will still access the app using the external port 49100, but it is now mapped to port 8080, which is what the app is listening to since the environment variable PORT was set.

Run it as a daemon

$ docker run -d -t -p 49100:3000 --name demo demo-app
dea4768765c176b679d1cb944fdf84466be17be7db0f749b47f5ab32a3ff2bc7

Naming containers is always a good idea, especially for daemons.

List it

$ docker ps

Stop it

$ docker stop demo

Remove it

$ docker rm demo

Steamlining the developer session workflow

During a development session, it can be time-consuming to continuously rebuild the image every time the sources are modified. The Dockerfile for the base node image configured the Node process in a running container to start in the /usr/src/app directory where the source files and modules under node_modules were copied in the image.

Using Docker's volume mapping feature, the current directory of your development system can be mapped to the /usr/src/app directory of a container so that the Node process running in the container uses the sources being edited.

$ docker run -d -t -p 49100:3000 --name demo -v $PWD:/usr/src/app demo-app

Using this technique, when a container is launched from the image and the Node process starts, it will be accessing /usr/src/app in a volume that has been mapped from the developer's system. There is no need to rebuild the image until the developer has tested the changes and is ready to publish a new image.

Mongo example

Create a Docker data volume container

$ docker create --name dbdata -v /dbdata mongo /bin/true

Start mongo

-without data volume container

$ docker run --name mongo -v /data/db -d mongo

-with data volume container

$ docker run -d --name mongo --volumes-from dbdata mongo

Connect with client container

$ docker run -it --link mongo:mongo --rm mongo sh -c 'exec mongo "$MONGO_PORT_27017_TCP_ADDR:$MONGO_PORT_27017_TCP_PORT/test"'

Backup database

$ docker run --rm --link mongo:mongo -v /root:/backup mongo bash -c 'mongodump --out /backup --host $MONGO_PORT_27017_TCP_ADDR'

$ docker-machine scp -r dev:~/test .

Node app container linking to mongo container

$ docker run -p 49100:3000 --link mongo:mongo demo-app

When launching your app container, Docker dynamically adds a mongo entry to the container's etc/hosts file and sets a number of convenient mongo-related environment variables, eliminating the need for you to have to provide configuration information. Here are all the environment variables that Docker created related to the mongo dependency in the previous command:

MONGO_ENV_MONGO_MAJOR=3.0  
MONGO_PORT=tcp://172.17.0.89:27017  
MONGO_ENV_MONGO_VERSION=3.0.3  
MONGO_PORT_27017_TCP=tcp://172.17.0.89:27017  
MONGO_PORT_27017_TCP_PROTO=tcp  
MONGO_PORT_27017_TCP_ADDR=172.17.0.89  
MONGO_NAME=/xapp/mongo  
MONGO_PORT_27017_TCP_PORT=27017  

In your app, you can create a connection URL to the Mongo test collection as simple as the following:

var mongoUrl = util.format('mongodb://mongo:%s/test', process.env.MONGO_PORT_27017_TCP_PORT);

Docker Machine reference
https://docs.docker.com/machine/

Docker Machine basics
http://atomiq.io/docker-machine/

Machine presentation (Nathan LeClaire)
https://www.youtube.com/watch?v=xwj44dAvdYo&feature=youtu.be

Docker Machine Drivers
https://docs.docker.com/machine/drivers/

Linking Containers
https://docs.docker.com/userguide/dockerlinks/

Best practices for writing Dockerfiles
https://docs.docker.com/articles/dockerfile_best-practices/

Node, Docker, and Microservices
http://atomiq.io/node-docker-and-microservices/
http://atomiq.io/microservices-with-node-and-docker/