Scala is an object-oriented programming language. It provides support to functional programming. It also helps to remove bugs in complex applications. In this article, you get to know about Scala and Scala Applications on Kubernetes. Running Containers at any real-world scale requires container orchestration, and scheduling platform like Docker Swarm, Apache Mesos, AWS ECS but the most popular out of it is Kubernetes. Kubernetes is an open-source system for automating deployment and management of containerised applications. Continuous delivery is a branch of continuous integration. It concentrates on automating the software delivery process so that teams can quickly and confidently deploy their code to production at any point.
It is an open-source platform that automates container operations, and Minikube is best for testing Kubernetes.
Kubectl is a command-line interface to manage Kubernetes cluster either remotely or locally. To configure kubectl on your machine follow this link.
Shared Persistent Storage
Shared Persistent Storage is permanent storage that we can attach to the Kubernetes container so that we don`t lose our data even when container dies. We will be using GlusterFS as the persistent data store for Kubernetes container applications.
Scala Application Source Code
Scala Application Source Code is source code that we want to run inside a Kubernetes container.
Dockerfile contains a bunch of commands to build PHP Laravel application.
The Registry is an online image store for container images. Below mentioned options are few most popular registries.
At the time of writing this blog, I haven`t got any official image of Scala sbt so I decided to build a base image for Scala sbt. In this image, we are using OpenJDK 8 as a development environment and Scala sbt 0.13.
FROM openjdk: 8
RUN apt - get update\ && apt - get install apt - transport - https - y
RUN echo "deb https://dl.bintray.com/sbt/debian /" | tee - a / etc / apt / sources.list.d / sbt.list\ && apt - key adv--keyserver hkp: //keyserver.ubuntu.com:80 --recv 2EE0EA64E40A89B84B2DF73499E82A75642AC823 \
&& apt - get update\ && apt - get install sbt - y\ && rm - rf /
var / lib / apt / lists /*
Building Scala Base Image
The Below mentioned command will build your scala base container image.
$ docker build -t scala-sbt:0.13
As Scala sbt doesn't have any official image of Docker container so we will be using above created image of Scala sbt as a base image for Scala applications.
FROM scala - sbt: 0.13
# Creating Home Directory in container
RUN mkdir - p / usr / src / app
# Setting Home Directory
WORKDIR / usr / src / app
# Copying src code to Container
COPY. / usr / src / app
# Compiling Scala Code
RUN sbt compile
# Exposing Port
# Running Scala Application
Building Scala Application Image
The below-mentioned command will build your application container image.
Reference Link for Pull and Push to Quay.io docker registry. Similarly, we can push or pull any container image to any of below-mentioned container registry like Docker Hub, AWS ECR, Private Docker Registry, Google Container Registry etc.
Now we have successfully deployed Scala Application on Kubernetes.
Verification of Dockerfile
We can verify application deployment either by using Kubectl or Kubernetes Dashboard. Below mentioned command will show you running pods of your application with status running/terminated/stop/created.
$ kubectl get po --namespace=<namespace kubernetes="" of=""> | grep <application name="">
Get the External Node Port using the below mentioned command. External Node Port is in the range from 30000 to 65000.
$ kubectl get svc--namespace = < namespace of kubernetes > | grep < application name >
Launch web Browser and open any of the below-mentioned URLs.
http://<kubernetes master ip address >: <application service port number>
http://<cluster ip address >: <application port number>
Check requirements/dependencies of the application.
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