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Let's containerize the wordsmith project!

The wordsmith project is split into 3 parts:

  • web: frontend web server written in Go
  • words: REST API written in Java, to query the DB
  • db: PostgreSQL database containing the words to display

Our goal is to containerize this application.

There will be 3 steps:

  1. Write multiple Dockerfiles. to build container images.
  2. Write a Compose file, to run the app locally.
  3. Deploy on Kubernetes.

Exercise 1: Dockerfiles

Our goal is to write Dockerfiles for the 3 containers.

First, git clone this repository. We need to create one Dockerfile for each service. Pro tip: place each Dockerfile in the corresponding directory (web, words, db).

The following paragraphs describe the installation instructions for each service.

Note: in this first exercise, we only want to build the images and check that they start correctly (web and words should display a short message to indicate that they're running), but we're not trying to run the whole application or to connect to the services. This will come later.

web

This is a web server written in Go. To compile Go code, we can use the golang official image, or install Go packages in any of the official base images.

The entire code is in a single source file (dispatcher.go), and should be compiled like this:

go build dispatcher.go

This creates an executable named dispatcher, which should be launched like this:

./dispatcher
Listening on port 80

The web server needs to access the static directory. This directory must be a subdirectory of the current working directory when the server is started.

Additional information:

  • the server listens on port 80
  • the Go compiler is only useful to build the server (not to run it)

words

This is a REST API backend written in Java. It should be built with maven.

On a Debian or Ubuntu distribution, we can install Java and maven like this:

apt-get install maven openjdk-8-jdk

To build the program, we can invoke maven like this:

mvn verify

The result is a file named words.jar, located in the target directory.

The server should be started by running the following command, in the directory where words.jar is located:

java -Xmx8m -Xms8m -jar words.jar

Additional information:

  • the server listens on port 8080
  • compilation requires packages maven and openjdk-8-jdk
  • execution requires package openjdk-8-jdk (maven is not necessary)

db

This is a PostgreSQL database.

The database must be initialized with the schema (database and tables) and the data (used by the application).

The file words.sql contains all the SQL commands necessary to create the schema and load the data.

# cat words.sql
CREATE TABLE nouns (word TEXT NOT NULL);
CREATE TABLE verbs (word TEXT NOT NULL);
CREATE TABLE adjectives (word TEXT NOT NULL);

INSERT INTO nouns(word) VALUES
  ('cloud'),
  ('elephant'),
  ('gø language'),
  ('laptøp'),
  ('cøntainer'),
  ('micrø-service'),
  ('turtle'),
  ('whale'),
  ('gøpher'),
  ('møby døck'),
  ('server'),
  ('bicycle'),
  ('viking'),
  ('mermaid'),
  ('fjørd'),
  ('legø'),
  ('flødebolle'),
  ('smørrebrød');

INSERT INTO verbs(word) VALUES
  ('will drink'),
  ('smashes'),
  ('smøkes'),
  ('eats'),
  ('walks tøwards'),
  ('løves'),
  ('helps'),
  ('pushes'),
  ('debugs'),
  ('invites'),
  ('hides'),
  ('will ship');

INSERT INTO adjectives(word) VALUES
  ('the exquisite'),
  ('a pink'),
  ('the røtten'),
  ('a red'),
  ('the serverless'),
  ('a brøken'),
  ('a shiny'),
  ('the pretty'),
  ('the impressive'),
  ('an awesøme'),
  ('the famøus'),
  ('a gigantic'),
  ('the gløriøus'),
  ('the nørdic'),
  ('the welcøming'),
  ('the deliciøus');

Additional information:

  • we strongly suggest using the official PostgreSQL image that can be found on the Docker Hub (it's called postgres)
  • if we check the page of that official image on the Docker Hub, we will find a lot of documentation; the section "Initialization scripts" is particularly useful to understand how to load words.sql
  • it is advised to set up password authentication for the database; but in this case, to make our lives easier, we will simply authorize all connections (by setting environment variable POSTGRES_HOST_AUTH_METHOD=trust)

Exercise 2: Compose file

When the 3 images build correctly, we can move on and write the Compose file. We suggest placing the Compose file at the root of the repository.

At this point, we want to make sure that services can communicate together, and that we can connect to web.

Note: the web service should be exposed.

Exercise 3: Spark Jobs

Run the local spark cluster using the docker compose from folder spark

Launch the spark jobs examples

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