Tag Archives: docker

The Kubernetes Guide For Java Developers: Part 1: Learn Kubernetes by deploying a real-world application on it

This is the guide I wish I had when I was starting my Kubernetes journey. Kubernetes is a complex technology with many new concepts that takes time to get your head around. In this guide, we will take an incremental approach to deploying applications on Kubernetes. We will cover what and why of Kubernetes and then we will learn how to deploy a real-world application on Kubernetes. We will first run application locally, then using Docker containers, and finally on Kubernetes. The guide will also cover Kubernetes architecture and important Kubernetes concepts like Pods, Services, Deployment.

In this guide, we will cover following topics:

  1. What is Kubernetes?
  2. The real reasons you need Kubernetes
  3. Kubernetes Architecture
  4. Deploying a real world application on Kubernetes

What is Kubernetes?

Kubernetes is a platform for managing application containers across multiple hosts. It abstracts away the underlying hardware infrastructure and acts as a distributed operating system for your cluster.

Kubernetes is a greek for Helmsman or Pilot (the person holding the ship’s steering wheels)

kubernetes-os

Kubernetes play three important roles:

  1. Referee
    • Kubernetes allocates and manages access to fixed resources using build in resource abstractions like Persistent Volume Claims, Resource Quotas, Services etc
    • Kubernetes provides an abstracted control plane for scheduling, prioritizing, and running processes.
    • Kubernetes provides a sandboxed environment so that applications do not interfere with each other.
    • Kubernetes allows users to specify the memory and CPU constraints on the application. It will ensure application remain in their limits.
    • Kubernetes provides communication mechanism so that services can talk among each other if required.
  2. Illusionist
    • Kubernetes gives the illusion of single infinite compute resource by abstracting away the hardware infrastructure.
    • Kubernetes provides the illusion that you need not care about underlying infrastructure. It can run on a bare metal, in data centre, on the public cloud, or even hybrid cloud.
    • Kubernetes gives the illusion that applications need not care about where they will be running.
  3. Glue
    • Kubernetes provides common abstractions like Services, Ingress, auto scaling, rolling deployment , volume management, etc.
    • Kubernetes comes with security primitives like Namespaces, RBAC that applications can use transparently

I learnt about the three roles – Referee, Illusionist, and Glue from the book Operating Systems Principles and Practices by Thomas Anderson and Michael Dahlin

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The Ultimate Dockerfile for Spring Boot Maven and Gradle applications

For Maven users, the ultimate Dockerfile is below.

FROM openjdk:8-jdk-alpine as build
WORKDIR /workspace/app

COPY mvnw .
COPY .mvn .mvn
COPY pom.xml .
RUN ./mvnw dependency:go-offline

COPY src src
RUN ./mvnw package -DskipTests
RUN mkdir -p target/dependency && (cd target/dependency; jar -xf ../*.jar)

FROM openjdk:8-jre-alpine
VOLUME /tmp
ARG DEPENDENCY=/workspace/app/target/dependency
COPY --from=build ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY --from=build ${DEPENDENCY}/META-INF /app/META-INF
COPY --from=build ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*","FULL_NAME_OF_SPRING_BOOT_MAIN_CLASS"]

Please make sure to update FULL_NAME_OF_SPRING_BOOT_MAIN_CLASS with Spring Boot application main class.

For Gradle users, the ultimate Dockerfile is below.

FROM openjdk:8-jdk-alpine as build
WORKDIR /workspace/app

COPY gradlew .
COPY gradle gradle
COPY build.gradle .
RUN ./gradlew dependencies

COPY src src
RUN ./gradlew build unpack -x test
RUN mkdir -p build/dependency && (cd build/dependency; jar -xf ../libs/*.jar)

FROM openjdk:8-jre-alpine
VOLUME /tmp
ARG DEPENDENCY=/workspace/app/build/dependency
COPY --from=build ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY --from=build ${DEPENDENCY}/META-INF /app/META-INF
COPY --from=build ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*","FULL_NAME_OF_SPRING_BOOT_MAIN_CLASS"]

Please make sure to update FULL_NAME_OF_SPRING_BOOT_MAIN_CLASS with Spring Boot application main class.

You can watch this video to learn more about optimizing docker images for Spring Boot applications.

Dockerizing a Vue.js application

It is common these days to run front-end and back-end services inside Docker containers. The front-end service usually talks using a API with the back-end service.

In this post we will cover following:

  1. Setting up a Docker based development environment with hot reloading
  2. Building a production ready Docker image with API url passed using environment variable

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How Docker uses cgroups to set resource limits?

Today, I was interested to know how does Docker uses cgroups to set resource limits. In this short post, I will share with you what I learnt.

I will assume that you have a machine on which Docker is installed.

Docker allows you to pass resource limits using the command-line options. Let’s assume that you want to limit the IO read rate to 1mb per second for a container. You can start a new container with the device-read-bps option as shown below

$ docker run -it --device-read-bps /dev/sda:1mb centos

In the above command, we are instantiating a new centos container. We specified device-read-bps option to limit the read rate to 1mb per second for /dev/sda device.

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Using wait-for-it with Oracle database docker image

Today, I was working with an application that uses Oracle as the database. We decided dockerize the application to make it easy for fellow developers to work with the beast. We found a working Oracle docker image by sath89. Oracle 12c Docker image is close to 5.7GB on disk so we are not talking about lightweight containers here :). Once image was dowloaded, running image was as easy as running the following command.
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Amazon ECS: The Modern Cluster Manager Part 1

In the last few posts, we looked at various Docker utilities and how XL Deploy can make it easy for enterprises to adopt and use Docker. Docker streamlines software development and testing for teams that have started embracing it. The package once deploy anywhere (PODA) capability of Docker minimises the issue of environmental (like staging, quality assurance, and production) differences. Continue reading

Upgrading Docker Compose to latest version

If you use Docker for Mac or something similar, Docker Compose will be installed along with it. Docker Compose has a different release timeline for Docker for Mac so you will not be able to try latest version of Docker compose until you upgrade Docker for Mac. This is limiting. You should be able to install Docker compose independently. To achieve that, you can run following command

$ composeVersion=1.13.0
$ curl -L https://github.com/docker/compose/releases/download/$composeVersion/docker-compose-`uname -s`-`uname -m` > /usr/local/bin/docker-compose$ chmod +x /usr/local/bin/docker-compose

In the above commands, $ signify bash prompt. You don’t have to type it. Now, you can check Compose version using the command shown below.

$ docker-compose version