Running scala in docker blog post

blogContent/posts/java/running-scala-code-in-docker.md

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+Alrighty, folks, this blog post is pretty straightforward from the title.
+We are going to be running [Scala](https://scala-lang.org/) code in [Docker](https://www.docker.com/) containers.
+Specifically, we will be using SBT and docker-compose.
+SBT is a built tool primarily used by Scala developers, and docker-compose is a tool for defining docker environments.
+
+To start, we need to create a simple Docker container that can build our scala code.
+From an existing Java JDK container, SBT is straightforward to install from a package manager.
+
+```bash
+FROM openjdk:8u232
+
+ARG SBT_VERSION=1.4.1
+
+# Install sbt
+RUN \
+  mkdir /working/ && \
+  cd /working/ && \
+  curl -L -o sbt-$SBT_VERSION.deb https://dl.bintray.com/sbt/debian/sbt-$SBT_VERSION.deb && \
+  dpkg -i sbt-$SBT_VERSION.deb && \
+  rm sbt-$SBT_VERSION.deb && \
+  apt-get update && \
+  apt-get install sbt && \
+  cd && \
+  rm -r /working/ && \
+  sbt sbtVersion
+
+RUN mkdir -p /root/build/project
+ADD build.sbt /root/build/
+ADD ./project/plugins.sbt /root/build/project
+RUN cd /root/build && sbt compile
+
+EXPOSE 9000
+WORKDIR /root/build
+
+CMD sbt compile run
+```
+
+There are a few things to note about this docker file.
+First, we are only adding the two SBT files and then running a simple SBT compile command when we build the container. 
+This SBT compile command only used to pull in general dependencies so that the end Docker container can launch faster.
+Second, notice that we are exposing port 9000; this port is only for the web application I am building. Finally, note that /root/build will be the root directory for the Scala SBT application.
+
+
+For reference, I include the two SBT files I'm using in this project:
+
+build.sbt:
+```bash
+name := """alert-api"""
+organization := "net.jrtechs"
+
+version := "1.0-SNAPSHOT"
+
+lazy val root = (project in file(".")).enablePlugins(PlayScala)
+
+scalaVersion := "2.13.2"
+
+resolvers += Resolver.JCenterRepository
+
+libraryDependencies += guice
+
+libraryDependencies += "net.katsstuff" %% "ackcord"                 % "0.16.1" //For high level API, includes all the other modules
+
+libraryDependencies += "org.scalatestplus.play" %% "scalatestplus-play" % "5.0.0" % Test
+
+libraryDependencies += "org.mongodb.scala" %% "mongo-scala-driver" % "2.9.0"
+```
+
+plugins.sbt:
+```bash
+addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.8.1")
+addSbtPlugin("org.foundweekends.giter8" % "sbt-giter8-scaffold" % "0.11.0")
+```
+
+Now that we have our docker file, we can create our docker-compose script to launch the application.
+For this application, I am attaching the container to a simple bridged network with a port exposed.
+
+```yaml
+version: '3.1'
+
+networks:
+  external-network:
+    external:
+      name: external-network
+
+services:
+
+  sbt:
+    build:
+      context: ./
+      dockerfile: ./docker/Dockerfile
+    image: sbt
+    ports:
+      - "9000:9000"
+    volumes:
+      - "./:/root/build"
+    networks:
+      - external-network
+```
+
+The main thing to note about the docker-compose script is that I placed our Dockerfile in a separate docker directory. Additionally, I'm mounting the scala project directory into the container as /root/build. The volume enables us to edit the project on our local machine while the Docker container compiles our code.
+
+To create the docker network, we need to issue this command -- it only needs to be run once.
+```bash
+docker network create -d bridge external-network
+```
+
+To run the project, we can use the docker-compose up command: 
+
+```bash
+docker-compose run
+```
+
+To use the SBT shell, we need to open a terminal to the running container. After we have the shell, we can issue all of our standard SBT commands.
+To properly forward the required ports when using docker-compose run, you need to pass in the "--service-ports" flag.
+
+```bash
+docker-compose run --service-ports sbt /bin/bash 
+sbt
+compile
+run
+```
+
+Since the location where we launch docker-compose is in the same directory as all of our scala code and build artifacts, we must create a ".dockerignore" file. Otherwise, Docker will scan the entire directory before building the container -- causing massive frustration. The "**" in the Docker ignore file tells Docker to ignore everything, and the "!" tells Docker to include that file. Alternatively, we could have just excluded the target build directory.
+
+```bash
+**
+!docker
+!build.sbt
+!project/plugins.sbt
+```
+
+That is it. I enjoy the docker approach towards developing Scala applications since it keeps the environment consistent across machines.
+As someone who enjoys distro-hopping, it is nice not having to figure out how to install Java, SBT, Scala, and countless other development environments on every operating system I use.
+I only need to install a text editor and Docker to develop projects with vastly different build environments and configurations. 
+All the complexity with setting up the environment can get relegated to the Docker container.
+
+This approach went over a container geared towards Scala development. For production, I would recommend that you use this SBT image to build a fat JAR, and then copy it into a lightweight JRE container using Docker's multi-stage build functionality.