Category Archives: Docker

Building, tagging and pushing Docker images with Maven

A standard use case for Docker is to build a container to run a pre-built application so that the containerized app can be run on any Docker enabled host. The application and the container are sometimes developed and built separately. First the application is built, then a container is defined and built to include the application. However, it can be better to promote the Docker container to a first-class build artifact. That is, the build process always builds the deployed component and its container at the same time. This saves a manual build step and also ensures that the Docker container is always up to date with the latest application build. It allows us to easily develop and test against the Dockerized application directly – every build results in a new deployable container.

There are a number of ways to do this. This article looks at hooking the Docker tasks into the Maven build process.

WebSocket push notifications with Node.js

The Node.js website describes it as having “an event-driven, non-blocking I/O model that makes it lightweight and efficient”. Sounds lovely, but what’s it actually for?

Modulus’s excellent blog post – An Absolute Beginner’s Guide to Node.js provides some rather tasty examples. After covering the trivial examples (Hello world! and simple file I/O), it gets to the meat of what we’re about – an HTTP server. The simple example demonstrates a trivial HTTP server in Node.js in 5 lines of code. Not 5 lines of code compiled to an executable or deployed into an existing web server. 5 lines of code that can be run from a simple command. It then goes on to describe the frameworks and libraries that let you do really useful stuff.

This looks just the thing for implementing a new feature in the Spanners demo app: push notifications to all logged-in users when a spanner is changed.

Docker Part 4: Composing an Environment Stack

This series of articles on Docker has so far covered a number of examples of creating and running individual Docker containers. We’ve also seen an example of how multiple Docker containers can be linked together using the –link command line flag.

Best practice for containerization suggests that each container does exactly one job. A full environment stack for a complex application may comprise many components – databases, web applications, web/micro services – each requiring its own container. Setting up the full working environment stack may require several lines of docker run commands, run in the right order, with just the right flags and switches set.

An obvious way to manage this is with a startup script. A neater solution is to use Docker Compose. Docker Compose allows multi-container applications to be defined in a single file and then started from a single command.

Docker Part 3: Disposable Containers

The previous posts in this series on Docker have looked at running containers to run services, specifically a web server and database server. However, Docker allows containers to be created, run, stopped and destroyed so cheaply that they can be used to run a single job. This job could be a script or even a single command. Unlike a service, a job will stop running when it’s complete. A container running a short lived job can be set to automatically stop and remove itself once the job is complete. If the job needs to be run again, it is reasonably efficient for Docker to start up a brand new container as required.

Docker Part 2: Building Images

The previous post in this series on Docker looked at starting up containers built from predefined images provided by Docker Hub. In this, the second in the series, I’ll look at creating customized images tailored to my specific requirements. I’ll also look at how my custom image can be pushed to Docker Hub for others to use.

Docker Part 1: Running Containers

Docker is a containerization technology that’s been getting quite a bit of attention over the last year or two. It offers a more lightweight, flexible and repeatable solution to creating and running Virtual Machines (VMs). In this, the first in a series of posts on Docker, I’ll look at how to run an application inside of a pre-built container image.