GitLab CI/CD - Hands-On Lab: Deploying Applications

Estimated time to complete: 15 minutes

Task A. Preparing Code

First, let’s make some small adjustments to our code so that it runs as a web application:

1. Open main.go.

2. Delete the existing code, and replace it with the following:

   package main
   
   import (
       "fmt"
       "log"
       "net/http"
   )
   
   func handler(w http.ResponseWriter, r *http.Request) {
       fmt.Fprintf(w, "Hi there")
   }
   
   func main() {
       http.HandleFunc("/", handler)
       log.Fatal(http.ListenAndServe(":80", nil))
   }
   

   This application will listen on port 80 for any requests to the “/” (root) endpoint. When it receives a request, it will print out the message Hi there.

   To accommodate our new application type, we will modify our CI/CD process by removing the tests to run the application binary. These tests will no longer work, as they will cause the application to pause and wait for connections. Instead, we will deploy this application to a test server to be able to test our application. To start, your CI/CD file should look like this:

       workflow:
       rules:
           - if: $CI_COMMIT_TAG
             when: never 
           - when: always
   
       default:
           image: golang
   
       include:
           - component: $CI_SERVER_FQDN/training-users/session-0a9ee9b9/iu6t0rjr/example-component/sample-template@v0.36.0
             inputs:
               stage: build
   
       stages:
           - test
           - build
           - run
           - release
           - deploy
   
       test go:
           stage: test
           script: go test array/ArrayUtils
           allow_failure: true
   
       build go:
           stage: build
           script:
               - go build
           artifacts:
               paths: 
               - array
           rules:
               - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
   
       run go:
           stage: run
           script:
               - ./array
           rules:
               - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
   
       release job:
           stage: release
           image: registry.gitlab.com/gitlab-org/release-cli:latest
           script:
               - echo "Generating the latest release!"
           release: 
               tag_name: 'v0.$CI_PIPELINE_IID'
               description: 'The latest release!'
           rules:
               - if: $CI_COMMIT_REF_NAME == $CI_DEFAULT_BRANCH
   
       deploy app:
           stage: deploy
           environment:
               name: prod
               url: "http://$ip:80"
           before_script:
               - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client git -y )'
               - eval $(ssh-agent -s)
               - chmod 400 "$SSH_PRIVATE_KEY"
               - ssh-add "$SSH_PRIVATE_KEY"
               - mkdir -p ~/.ssh
               - chmod 700 ~/.ssh
           script:
               - ssh-keyscan -t rsa,ed25519 $ip >> ~/.ssh/known_hosts
               - ssh root@$ip 'ls /'
   

3. To ensure we have access to the build artifact in the deploy job, remove the run condition (rules block) from the job:

   build go:
       stage: build
       script:
           - go build
       artifacts:
           paths:
               - array
   

Task B. The Deployment Process

We now have an SSH connection working between the GitLab runner and our target server. The final step we have is to deploy our application to the server! Ideally, we would only do this on commits to the default branch.

1. Start by adding a rule to only run the deploy job on default branch commits.

   deploy app:
       stage: deploy
       image: ubuntu:latest
       before_script:
           - "which ssh-agent || ( apt-get update -y && apt-get install openssh-client git -y )"
           - eval $(ssh-agent -s)
           - chmod 400 "$SSH_PRIVATE_KEY"
           - ssh-add "$SSH_PRIVATE_KEY"
           - mkdir -p ~/.ssh
           - chmod 700 ~/.ssh
       script:
           - ssh-keyscan -t rsa,ed25519 $ip >> ~/.ssh/known_hosts
           - ssh root@$ip 'ls /'
       environment:
           name: prod
           url: "http://$ip:80"
       rules:
           - if: $CI_COMMIT_REF_NAME == $CI_DEFAULT_BRANCH
   

   To be able to launch and maintain the execution of our web application, we will need to add it as a system service for our server. To achieve this, we will write a simple system service.

2. Create a new file at the root of your project named array.service. In this file, add the following text:

   [Unit]
   Description=
   After=network.target
   
   [Service]
   Type=simple
   ExecStart=/www/array
   
   [Install]
   WantedBy=multi-user.target
   

   Our code will need to move the array binary to the www directory, and move the service definition file to the /lib/systemd/system directory. To achieve this, you can use scp.

   deploy app:
       stage: deploy
       image: ubuntu:latest
       before_script:
           - "which ssh-agent || ( apt-get update -y && apt-get install openssh-client git -y )"
           - eval $(ssh-agent -s)
           - chmod 400 "$SSH_PRIVATE_KEY"
           - ssh-add "$SSH_PRIVATE_KEY"
           - mkdir -p ~/.ssh
           - chmod 700 ~/.ssh
       script:
           - ssh-keyscan -t rsa,ed25519 $ip >> ~/.ssh/known_hosts
           - ssh root@$ip 'mkdir -p /www'
           - ssh root@$ip 'test -e /www/array && rm -f /www/array || echo "No existing /www/array to delete"'
           - scp array root@$ip:/www
           - scp array.service root@$ip:/lib/systemd/system/
           - ssh root@$ip 'ls /www'
           - ssh root@$ip 'ls /lib/systemd/system'
           - ssh root@$ip 'systemctl enable array.service'
           - ssh root@$ip 'systemctl restart array.service'
           - ssh root@$ip 'systemctl status array.service'
       environment:
           name: prod
           url: "http://$ip:80"
       rules:
           - if: $CI_COMMIT_REF_NAME == $CI_DEFAULT_BRANCH
   

3. After the pipeline has successfully completed, you can navigate to Operate > Environments , and see your environment has been deployed. Click on the Open button to access your newly deployed application.

Lab Guide Complete

You have completed this lab exercise. You can view the other lab guides for this course.

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