Introduction to DOCKER

Esandi Linara — Fri, 18 Sep 2026 11:10:29 +0000

What is Docker?

Docker is a tool that lets the user to package up an application along with everything it needs to run. The code, the libraries, the settings, all of it are put into a single neat unit called a container.

Why do people use Docker?

Docker exists to kill the "works on my machine" excuse. It does this by packaging apps so they run the same everywhere, making deployment a one-step process, letting each part of an app (database, backend, frontend) run in its own container, keeping teams on the same setup, and fitting neatly into automated testing/deployment pipelines.

Advantages of Docker

Portable: build once, run anywhere
Lightweight and fast to start
Keeps apps isolated from each other
Speeds up releases
Scales easily with tools like Kubernetes
Supports easy version rollbacks
Runs efficiently without multi-OS overhead
Backed by a huge community and ready-made images

Disadvantages of Docker

Carries kernel-level security risk
Can't truly virtualize a different OS
Makes long-term data storage trickier
Adds networking complexity at scale
Has a real learning curve
Harder to debug than a normal app
Small performance cost vs. running natively

What is Docker Hub?

Docker Hub is basically the app store for Docker images. It is a cloud-based library where people can upload, share, and download container images.

It lets the user to store images publicly for free or keep them private with a paid plan. It gives you access to official, verified images for popular software like MySQL, Nginx, Python, and Node. It can automatically rebuild the images whenever you push new code to GitHub, and lets you label images with version tags so you always know exactly what you're running. It is a container, what GitHub is to code a central place to find, share and build on other people's work.

Maven Basics

Esandi Linara — Fri, 18 Sep 2026 10:15:52 +0000

1. What is Maven?

Maven is a tool that helps to build and manage Java projects. It handles things like downloading the libraries that project needs, compiling the code, running the tests, and packaging everything into a final file called .jar. Instead of doing all of this manually, Maven does it for you based on a set of rules written in a file called pom.xml.

2. Advantages of Maven

Maven downloads the libraries (dependencies), project needs straight from the internet, so there is no need to add them by hand.
Maven has standard project structure so that every Maven project follows the same folder layout, so any developer can jump into a new project and immediately know where things are.
Maven has an easy build process so that a single command like mvn install can compile the code, run the tests, and package the whole project.
Maven has a huge ecosystem of plugins for testing, reporting, deployment, and more.

3. How do you install Maven?

First, I made sure Java (JDK) was installed, since Maven needs it to run:java -version
Then I updated my package list and installed Maven directly using apt:sudo apt update
sudo apt install maven
Once it finished installing, I confirmed everything worked by checking the version: mvn -version

4. Display output of maven version

Apache Maven 3.9.6
Maven home: /usr/share/maven
Java version: 17.0.10, vendor: Ubuntu
Java home: /usr/lib/jvm/java-17-openjdk-amd64
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "6.5.0", arch: "amd64"

The above output says the Maven version, the Java version it's linked to, and some basic OS details.

5. The 3 Types of Maven Repositories

(i) Local Repository — A folder on the own computer, where Maven stores every library it downloads. Once something's downloaded once, Maven just reuses it from here instead of re-downloading it every time you build.

(ii) Central Repository — The default, public repository on the internet (Maven Central) containing thousands of common libraries. If something isn't already in your local repository, Maven looks here next.

(iii) Remote Repository — A private or custom repository set up by a company or team, often using tools like Artifactory. This is useful for internal libraries that aren't meant to be public, or for controlling exactly which versions of dependencies are approved for use across a team.

6. Running Unit Tests with Maven

The command is as follows:

mvn test

This compiles the code and runs every test class found under src/test/java. Under that, Maven uses a plugin called "Surefire" to actually execute the tests, and gives an output as follows:

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
BUILD SUCCESS

If a test fails, the output is as BUILD FAILURE, along with details on exactly which test failed and why, which makes the debugging pretty straightforward once I understood how to read the output.

DEV Community: Esandi Linara

Introduction to DOCKER

Maven Basics