🎯 Lab Objective
Build a full CI/CD pipeline that:
- Connects GitLab to Mac terminal
- Builds Docker image
- Pushes image to GitLab Registry
- SSH into EC2
- Deploys container
- Handles real-world production errors
🏗️ Architecture
CODE
Mac Terminal
↓
GitLab Repo
↓
GitLab CI/CD Pipeline
↓
Docker Image Build
↓
Push to GitLab Container Registry
↓
SSH to AWS EC2
↓
Docker Pull & Run
↓
Application Live on Port 80
🔹 STEP 1 — GitLab Pages Basic Pipeline
We had:
.gitlab-ci.yml
CODE
image: busybox
pages:
stage: deploy
script:
- echo "The site will be deployed"
artifacts:
paths:
- public
rules:
- if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
Trigger pipeline:
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git commit --allow-empty -m "Trigger pipeline"
git push origin master
🔹 STEP 2 — Add Docker Build Stage
Create Dockerfile (ROOT of project):
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FROM nginx:alpine
COPY public /usr/share/nginx/html
EXPOSE 80
Update .gitlab-ci.yml:
CODE
stages:
- build
- push
- deploy
variables:
IMAGE_NAME: registry.gitlab.com/$CI_PROJECT_PATH:latest
build_image:
stage: build
image: docker:24
services:
- docker:24-dind
script:
- docker build -t $IMAGE_NAME .
🔹 STEP 5 — Push to GitLab Container Registry
Add:
CODE
push_image:
stage: push
image: docker:24
services:
- docker:24-dind
script:
- echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER --password-stdin $CI_REGISTRY
- docker push $IMAGE_NAME
🔴 ERROR #1 — Image Not Found
Error:
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An image does not exist locally with the tag
Fix:
Make sure build and push stages use SAME $IMAGE_NAME.
🔹 STEP 6 — Deploy to AWS EC2
Deploy stage:
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deploy_ec2:
stage: deploy
image: alpine
before_script:
- apk add --no-cache openssh
script:
- echo "$EC2_KEY" > key.pem
- chmod 600 key.pem
- ssh -o StrictHostKeyChecking=no -i key.pem ubuntu@$EC2_HOST "
docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY &&
docker pull $IMAGE_NAME &&
docker stop web || true &&
docker rm web || true &&
docker run -d -p 80:80 --name web $IMAGE_NAME
"
🔴 ERROR #2 — SSH Hostname Not Resolved
Cause:
CI/CD variables not set.
Fix:
Go to:
Settings → CI/CD → Variables
Add:
Variable 1
Key: EC2_HOST
Value: EC2 Public IP
Variable 2
Key: EC2_KEY
Value: FULL .pem file content
Important:
- NOT protected
- Visible
- Separate variables
🔴 ERROR #3 — Port 80 Already in Use
Pipeline error:
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failed to bind host port 80
address already in use
SSH into EC2:
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sudo lsof -i :80
Found:
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nginx running
Fix:
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sudo systemctl stop nginx
sudo systemctl disable nginx
Re-run pipeline → SUCCESS.
🔹 Final Result
App accessible at:
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http://EC2_PUBLIC_IP
🧠 Real DevOps Troubleshooting Lessons
You debugged:
| Issue | Tool Used |
|---|---|
| SSH denied | ssh-add |
| Pipeline variable missing | GitLab CI/CD variables |
| Docker tag mismatch | Inspect IMAGE_NAME |
| SSH hostname error | Check variables |
| Port conflict | lsof -i :80 |
| Nginx conflict | systemctl stop |
This is REAL production debugging.
🎓 Interview Explanation Version
If interviewer asks:
"How would you deploy using GitLab CI/CD to EC2?"
You answer:
- Create Dockerfile
- Configure multi-stage pipeline
- Build image
- Push to registry
- Store SSH key & host as CI variables
- Use SSH in deploy stage
- Handle container replacement safely
- Troubleshoot port conflicts
- Ensure idempotent deployment
That is senior-level answer.
Vollständiger Original-Artikel
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