<\/span><\/h2>\n\n\n\nLet’s see how to create an image that runs a web application based on Express.js (a minimalist framework for building web applications with Node.js).<\/p>\n\n\n\n
A Dockerfile always begins with the FROM<\/code> instruction, which indicates the base image we will use. We will start with a Ubuntu Linux distribution:<\/p>\n\n\n\nFROM ubuntu:20.04<\/code><\/pre>\n\n\n\nIt is possible to start from scratch by using “FROM scratch”.<\/p>\n\n\n\n
Next, we will use the RUN<\/code> instruction to execute commands in our container.<\/p>\n\n\n\nWe will install Node.js, install npm (useful for installing Express.js), create a folder for our web application, and finally install Express.js:<\/p>\n\n\n\n
RUN apt-get update \\\n\t&& apt-get install -y nodejs \\\n\t&& apt-get install -y npm \\\n\t&& mkdir myapp && cd myapp && npm init -y && npm install express<\/code><\/pre>\n\n\n\nEach instruction in a Dockerfile results in the creation of a layer.<\/p>\n\n\n\n
The number of layers impacts the size of the images, so here we limit the number of instructions by executing multiple commands within a single RUN<\/code> instruction.<\/p>\n\n\n\nNote: The maximum number of layers is limited to 128.<\/p>\n\n\n\n
Our goal is to create a small and pointless web application in Node.js that simply returns “Hello World!” hardcoded:<\/p>\n\n\n\n
const express = require('express')\nconst app = express()\nconst port = 80\n\napp.get('\/', (req, res) => {\n res.send('Hello World!')\n})\n\napp.listen(port, () => {\n console.log(`Up`)\n})<\/code><\/pre>\n\n\n\nWe will add this file to the image:<\/p>\n\n\n\n
COPY app.js \/myapp\/app.js<\/code><\/pre>\n\n\n\nNext, we will change the current directory:<\/p>\n\n\n\n
WORKDIR \/myapp<\/code><\/pre>\n\n\n\nWe will set the listening port for our application:<\/p>\n\n\n\n
EXPOSE 80<\/code><\/pre>\n\n\n\nIn itself, EXPOSE doesn’t do anything at the image level, but it serves two purposes:<\/p>\n\n\n\n
Documentation: People who view the Dockerfile can know which ports they need to map.
CMD [\"node\", \"app.js\"]<\/code><\/pre>\n\n\n\nHere is our complete Dockerfile:<\/p>\n\n\n\n
FROM ubuntu:20.04\n\nRUN apt-get update \\\n\t&& apt-get install -y nodejs \\\n\t&& apt-get install -y npm \\\n\t&& mkdir myapp && cd myapp && npm init -y && npm install express\n\nCOPY app.js \/myapp\/app.js\n\nWORKDIR \/myapp\n\nEXPOSE 80\n\nCMD [\"node\", \"app.js\"]<\/code><\/pre>\n\n\n\nOur Dockerfile is already written! Now, all that’s left is to create our image using the “docker build” command:<\/p>\n\n\n\n
docker build -t cyrilbois\/mywebapp:latest .<\/code><\/pre>\n\n\n\nThe “-t” option allows us to specify the name (and tag) of our image.<\/p>\n\n\n\n
Our image is finally created! \ud83d\ude0a<\/p>\n\n\n\n
If we want to create a container from our image:<\/p>\n\n\n\n
docker run -d -p 3000:80 --name webapp cyrilbois\/mywebapp:latest<\/code><\/pre>\n\n\n\nNow, we can access our web application:<\/p>\n\n\n\nAnd there you have it! I hope this tutorial was helpful.<\/p>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
In this tutorial, we will focus on creating an image from a Dockerfile. I will cover the writable layer of containers in a separate article.<\/p>\n","protected":false},"author":1,"featured_media":226,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_sitemap_exclude":false,"_sitemap_priority":"","_sitemap_frequency":""},"categories":[2],"tags":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/posts\/241"}],"collection":[{"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/comments?post=241"}],"version-history":[{"count":2,"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/posts\/241\/revisions"}],"predecessor-version":[{"id":274,"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/posts\/241\/revisions\/274"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/media\/226"}],"wp:attachment":[{"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/media?parent=241"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/categories?post=241"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/extendsclass.com\/blog\/wp-json\/wp\/v2\/tags?post=241"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}