Implementation of CI/CD in Java application(Linux) Using Shell and Docker Executor on GitLab

There are many executors available to implement CI/CD with GitLab Runner. However, Shell and Docker are more popular among them, and we can easily configure a repository with these runners.  These runners can be chosen based on the requirements and availability of the resources. This article mainly focuses on Shell and Docker executors of Java Linux application and code is written in bash script. The application can build and test using a bash script.

Shell Executor: Shell Executor is a very simple executor which helps to build the solution locally on the machine, where GitLab Runner is installed. In this case, GitLab Runner is installed on Linux Machine, so need to install the required software in the same system.

Docker Executor: It is a powerful tool that includes much software and it can be accessed by image. The advantage of this executor is that, we do not need to install any software manually, everything will be taken care of through docker and the required image will be downloaded from the docker hub. However, the disadvantage is that this communication is blocked in some organizations due to security purposes. So, If this is the case Shell Executor is the best alternative. 

Implementation of Java on Shell Executor:

Requirements: These are the basic software that needs to install on a Linux machine. However, it can be changed based on the compilation script and need to download other software if needed.

Software	Description
Git	This is the first requirement, to commit the changes on GitLab. It is a version control software that tracks the changing set of files
JDK	Need to install a specific version of JDK  on the machine which you have targeted, to build the jar file. For example, OpenJDK-8
Apache Ant	This is a tool that helps to build processes and generate the jar file of the project while running this file. It contains more information about the project and add this information inside the jar.

Path Configuration: After successful installation, you need to set the path of this installed software in the machine, if it is not set. Run the below command on the machine.

Variable / File	Path
Git	Set the path of Git in the Linux machine, if it already not set. Can check with which git export Git = /usr/bin/git
JAVA	export JAVA=/usr/bin/java      Can check with which java
Apache Ant	export ANT=/usr/bin/ant       Can check with which ant
Permission	Give Permission to build.xml before it runs:  chmod -R 777 *
build.xml	It will build the project, and generate the jar based on containing information
.gitlab-ci.yml	This file should be inside the root directory of the project which contains all the CI/CD configuration including software and script path. Here, you can mention how this repository should run. Before adding this file to the root directory, should check it is a valid yml file or not.

GitLab Runner Set Up: Follow the below steps to download and configure the GitLab Runner.

1. Download GitLab Runner on Linux Machine 

sudo curl -L --output /usr/local/bin/gitlab-runner https://gitlab-runner-downloads.s3.amazonaws.com/latest/binaries/gitlab-runner-linux-amd64

2. Give it permissions to execute using the following command:

sudo chmod +x /usr/local/bin/gitlab-runner

3. Create a GitLab CI use the following command:

sudo useradd --comment 'GitLab Runner' --create-home gitlab-runner --shell /bin/bash

4. Install and run as a service using the following command:

sudo gitlab-runner install --user=gitlab-runner --working-directory=/home/gitlab-runner

5. Start GitLab Runner using the following command:

sudo gitlab-runner start

6. Stop the GitLab Runner before registering the repository using the following command:

sudo gitlab-runner stop

7. Once GitLab Runner is successfully stopped enter the following command in the terminal for repository registration.

sudo gitlab-runner register

8. When you do repository registration with GitLab Runner, the below questions have to answer.

• Enter your GitLab instance URL: It can be different with each organization and the format will be like http://gitlab.example.com     
• Path: Go to GitLab Account → Select repository which you want to register with runner → Settings → CI/CD → Expand Runner
• Enter the gitlab-ci token for this runner: It will be a unique token of each project which will need while registration and it can be found      
• Path: Go to GitLab Account → Select repository which you want to register with runner → Settings → CI/CD → Expand Runner
• Enter the gitlab-ci description for this runner: Put Runner name(any name), which will help you to remember that which runner’ is running
• Enter the gitlab-ci tags for this runner: It is optional if you want to start GitLab runner when a specific tag is available in yml file.
• Enter the executor: There will be a list of several executors, and type shell(as GitLab Runner will run our system)

9. After successful registration, start the GitLab Runner using the following command

sudo gitlab-runner start

To verify that GitLab Runner has registered the respective repository and the runner has been started. Go to GitLab Account → Select repository which you want to register with runner → Settings → CI/CD → Expand Runner, There will be a green color circle will be available, and displaying message will be Runners activated for this project.  

Note: If the circle is gray, it means the runner has not started and starts again.

Linux GitLab Runner Commands

Command	Description
sudo gitlab-runner register	Register the project with GitLab Runner
sudo gitlab-runner register	Start the runner
sudo gitlab-runner stop	Stop the runner
sudo gitlab-runner status	To know the status of gitlab-runner
sudo gitlab-runner unregister –name  test-runner	Unregister the Runner of a project and replace the test-runner with your runner name and this name can be found inside the config.toml file (where your gitlab-runner ) available.
sudo gitlab-runner unregister –url http://gitlab.example.com/ –token t0k3n	Remove Runner by URL and token
sudo gitlab-runner unregister –all-runners	Unregister All Runners
sudo gitlab-runner restart	This command stops and then starts the GitLab Runner service
sudo gitlab-runner uninstall	This command stops and uninstalls the GitLab Runner from being run as a service
sudo gitlab-runner exec	To see a list of available executors, run
sudo gitlab-runner –help	Check a recent list of commands by executing
sudo gitlab-runner run –help	Can see the name of the environment variable
sudo gitlab-runner –debug	To run a command in debug mode
sudo gitlab-runner exec shell	To see a list of all available options for the shell executor, run

.gitlab-ci.yml_shell Executor: Below is the content of .gitlab-ci.yml on shell executor mode. However, change it if needed based on requirements.

stages:
 - build
 - execute

build:
 stage: build
 script:  
   - ant -f build.xml
 
 artifacts:
   paths:
   - abc.jar

execute:
 stage: execute
 script:  
  - pwd  
  - cd scripts
  - chmod -R 777 *
  - pwd  
  - ./run.sh

Implementation of Java on Docker Executor: There is no need to install any software manually, everything will be taken from the docker container. However, you can install the required software inputting the name in yml file and also can export the path. To run the GitLab runner on docker executor mode, Go to GitLab Runner Set-Up(above), and select docker instead of shell.

.gitlab-ci.yml_ Docker Executor:  Below are the content of .gitlab-ci.yml on docker executor mode. However, change it if needed. 

image: ubuntu:latest

stages:
 - build
 - execute
 
before_script:
 - echo "Before script section"
 - apt-get update && apt-get -y install openjdk-8-jdk  && apt-get -y install ant
 
 
build:
 stage: build
 script:  
   - ant -f build.xml
 
 artifacts:
   paths:
   - abc.jar

execute:
 stage: execute
 script:  
  - pwd  
  - cd scripts
  - chmod -R 777 *
  - pwd  
  - ./runtest.sh