Go Web Application with K8S & GitLab CI/CD

A simple Go web application that serves a "Hello from Go!" message. This project includes Dockerization, Kubernetes deployment manifests for dev and prod environments, and a GitLab CI/CD pipeline with automated testing and deployment.

Project Structure

k8s-project
├── main.go
├── Dockerfile
├── test.sh
├── gitlab-ci.yml
├── .gitignore
├── .dockerignore
├── test/
│   └── gitlab-test.yml
├── k8s/
│   ├── dev/
│   │   ├── ConfigMap.yaml
│   │   ├── Service.yaml
│   │   ├── Deployment.yaml
│   │   └── Ingress.yaml
│   └── prod/
│       ├── ConfigMap.yaml
│       ├── Service.yaml
│       ├── Deployment.yaml
│       └── Ingress.yaml
└── README.md

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Prerequisites

Before you begin, ensure you have the following:

• A GitLab account and project repository.
• Access to a private Docker registry (e.g., Nexus, Harbor) at docker.registry.local.
• A Kubernetes cluster with kubectl configured.
• GitLab CI/CD variables set:
  • NEXUS_USER: Username for Docker registry.
  • NEXUS_PASSWORD: Password for Docker registry.
  • KUBE_CONFIG: Base64-encoded kubeconfig file for cluster access.

You can set these variables in GitLab > Settings > CI/CD > Variables.

Configure Containerd to Use Private Registry

Since your images are pushed to a private registry (docker.registry.local), you must configure containerd on all Kubernetes worker nodes to trust this registry.

Step 1: Edit containerd config

On each worker node, edit /etc/containerd/config.toml:

sudo vim /etc/containerd/config.toml

[plugins."io.containerd.grpc.v1.cri".registry]
      config_path = "/etc/containerd/certs.d"

Then create this directory

mkdir /etc/containerd/certs.d

In there you will always need a new directory for every registry that you want to mirror. Examples would be registry.k8s.io or docker.io.

mkdir /etc/containerd/certs.d/registry.k8s.io
mkdir /etc/containerd/certs.d/docker.io

In this directory you need to create a hosts.toml with the following content

[host."http://docker.registry.local"]
	capabilities = ["pull", "resolve"]

kubectl create secret docker-registry regcred \
  --docker-server=docker.registry.local \
  --docker-username=$NEXUS_USER \
  --docker-password=$NEXUS_PASSWORD \
  --docker-email=your-email@example.com \
  -n dev

kubectl create secret docker-registry regcred \
  --docker-server=docker.registry.local \
  --docker-username=$NEXUS_USER \
  --docker-password=$NEXUS_PASSWORD \
  --docker-email=your-email@example.com \
  -n prod

Add imagePullSecrets to Your Deployments:

Update your k8s/dev/Deployment.yaml and k8s/prod/Deployment.yaml files to include:

spec:
  template:
    spec:
      imagePullSecrets:
        - name: regcred

Step 2: Restart containerd

sudo systemctl restart containerd

---

How to Run Tests Locally

1. Make sure you have Go installed (go version).
2. Run the test script:

chmod +x test.sh
./test.sh

This will start the Go server locally on port 80 and verify it returns "Hello from Go!".

---

Deploy to Kubernetes

1. Manual Deployment (for testing)

For Development:

kubectl apply -f k8s/dev/

For Production:

kubectl apply -f k8s/prod/

Ensure namespaces dev and prod exist:

kubectl create namespace dev
kubectl create namespace prod

---

GitLab CI/CD Pipeline

The pipeline has 5 stages:

Stage	Description	Trigger Condition
build_dev	Builds and pushes image tagged with $CI_PIPELINE_ID	On dev branch
test	Runs unit/integration tests via test/gitlab-test.yml	On dev, master, tags
deploy_dev	Deploys to dev namespace	On dev branch
build_prod	Builds and pushes image tagged with $CI_COMMIT_TAG	On master or tags
deploy_prod	Deploys to prod namespace (manual trigger)	On tags only

Automatic Deployment

• Every commit to the dev branch triggers:
  • Build → Test → Deploy to dev namespace.

Manual Deployment to Production

1. Create a Git tag (e.g., v1.0.0) and push it:

git tag v1.0.0
git push origin v1.0.0

2. In GitLab, go to CI/CD > Pipelines, find the pipeline for the tag, and manually trigger the deploy_prod job.

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Notes

• All Docker images are pushed to the private registry: docker.registry.local/go-k8s-project:<tag>.
• The test stage is modular and defined in test/gitlab-test.yml (as requested).