Learn how to build a simple Node.js web server with Docker. In this lesson, we'll create a Dockerfile for a simple Node.js script, copy and build it into a Docker image, and start a container to run the web server.
We have a simple express server:
// Load the http module to create an http server. var http = require('http'); // Configure our HTTP server to respond with Hello World to all requests. var server = http.createServer(function (request, response) { response.writeHead(200, {"Content-Type": "text/plain"}); response.end("Hello World "); }); // Listen on port 8000, IP defaults to 127.0.0.1 server.listen(8000); // Put a friendly message on the terminal console.log("Server running at http://127.0.0.1:8000/");
Create a DockerFile:
A Docker file is a text document which provides the Docker engine with instructions on how to build the image. Every Docker file starts with the "from" keyword, followed by the name of our base image. A base image is another Docker image from which we'll build our image. Since we're running a Node web server, we'll use the mhart/alpine-node image as our base.
FROM mhart/alpine-node
Then we say "copy" our main enter file to our image:
COPY index.js .
By default, you can think of Docker as having a firewall with no ports opened. Since we're running a web server, we'll need to open up the port the server is running on.
Let's add "expose 8000" to our Docker file.
EXPOSE 8000
The last line in every Docker file is typically the "cmd" or "command" keyword, followed by our executable. We'll use a simple command to start our web server, "Node index.js." This is now a valid Docker file.
CMD node index.js
Full:
FROM mhart/alpine-node COPY index.js . EXPOSE 8000 CMD node index.js
Next, we'll use it to build our Docker image. From our project directory, run "Docker build -t myserver."
docker build -t myserver .
-t: to name our docker image.
.: to tell which dir to look
After executing it, you can verify the image was built by running:
docker images
We can test it by running "Docker run." We'll also specify a "-p" flag, which maps a host port to a container port.
You can think of this as port forwarding through a firewall. Let's map port 8000 on our host to port 8000 on our container. Lastly, we'll add the name of our Docker image we specified when we built our image, "myserver."
docker run -p 8000:8000 myserver