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

01 Mar, 2021
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.
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.
Set the path of Git in the Linux machine, if it already not set. Can check with which git 
export Git = /usr/bin/git   
export JAVA=/usr/bin/java     
Can check with which java
export ANT=/usr/bin/ant      
Can check with which ant
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.
  .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
Advanced Computer Subject
Git
Java
Linux-Unix
Java
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