How to create a microservice with Node + Express.js, Docker and MongoDB

This example contains a simplified version of a Product object CRUD running on a Node + Express.js API server.

For development and testing purpose the repository is ForeRunnerDB.

The Dockerfile defines the instructions for building the server image and its process is documented step by step. Open it to read all the commands.

Dockerizing the microservice

A brief introduction to the Docker platform

After installing Docker, a new host's network stack is created with the name docker0. Using the command ifconfig you find it among the others current network interfaces.

On the next bash lines you can see the assigned IP address 172.17.0.1 to the docker0 network.

docker0   Link encap:Ethernet  HWaddr 02:42:40:0e:9d:2d  
          inet addr:172.17.0.1  Bcast:0.0.0.0  Mask:255.255.0.0
          inet6 addr: fe80::42:40ff:fe0e:9d2d/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1701 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1801 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:345486 (345.4 KB)  TX bytes:279213 (279.2 KB)

Containers are connected by default using this interface called bridge and can communicate with each other using their IP addresses.

In order to connect two containers the Docker run command has the --link option.

Your application and their databases can then be decoupled and managed in two different Docker containers.

For this example the app container image will be generated from a node 7 image and the database container will be created directly from a mongo 3.4 image.

First of all download the images for mongo and node with the following two commands:

sudo docker pull mongo:3.4
sudo docker pull node:7

After downloading them, use the command below if you want to watch their informations:

sudo docker images

For mongo you just need to create an instance of the downloaded image. Using the Docker run command you can start it:

sudo docker run -d -p 28018:27017 --name MongoDB mongo:3.4

The -d option daemonizes the container process which has the MongoDB name. The exposed port 27017 will be explicitly mapped to the host 28018 port.

Now it's time to use the Dockerfile to build the server image. From the server folder then give the following command:

sudo docker build -t claclacla/microservice .

After building, you can run a daemonized claclacla/microservice container using the -d option with the name Microservice. Map the exposed port 8080 to the host port 4000 and finally connect it to the mongo container with the --link option.

sudo docker run -d -p 4000:8080 --link=MongoDB:MongoDB --name Microservice claclacla/microservice

If you want to watch the result of these commands, connect to the running container in interactive mode using the command below:

sudo docker exec -it Microservice /bin/bash

Read the container hosts file with the next command:

cat /etc/hosts

You should have an output similar to the following:

127.0.0.1	localhost
::1	localhost ip6-localhost ip6-loopback
fe00::0	ip6-localnet
ff00::0	ip6-mcastprefix
ff02::1	ip6-allnodes
ff02::2	ip6-allrouters
172.17.0.2	MongoDB e2eb0c886f9e
172.17.0.4	d2954b3fa17c

Note the MongoDB mapped address.

During the containers linking Docker also creates environment variables. With the command below:

env | grep MONGODB

You should find the following two defined variables:

MONGODB_PORT_27017_TCP_PORT=27017
MONGODB_PORT_27017_TCP_ADDR=172.17.0.2

Prerequisites

What things you need to install the software

Docker 17.0+

Installing

The easiest way to get started is to clone the repository.

# Get the latest snapshot
git clone https://github.com/claclacla/How-to-create-a-microservice-with-Node-+-Express.js,-Docker-and-MongoDB

# Change directory
cd How-to-create-a-microservice-with-Node-+-Express.js,-Docker-and-MongoDB

# Install NPM dependencies
npm i

# Download mongo and node images
sudo docker pull mongo:3.4
sudo docker pull node:7

# Run a mongo container
sudo docker run -d -p 28018:27017 --name MongoDB mongo:3.4

# Build a server image
sudo docker build -t claclacla/microservice .

# Run a server container
sudo docker run -d -p 4000:8080 --link=MongoDB:MongoDB --name Microservice claclacla/microservice

Usage

# Change directory
cd How-to-create-a-microservice-with-Node-+-Express.js,-Docker-and-MongoDB

# Test it using...

npm run e2e-test
# ...to test the collections API

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