CI/CD Gitlab

Certainly! Let's dive deep into GitLab CI/CD YAML configuration files (.gitlab-ci.yml) and understand every important component in detail. This file is the backbone of GitLab's automation features for CI/CD (Continuous Integration / Continuous Deployment). I’ll also clarify “Nestor” (possibly a confusion with GitLab features — I’ll address it below).

---

🔧 1. What is .gitlab-ci.yml?

The .gitlab-ci.yml file is the configuration file GitLab uses to define pipelines, which are collections of jobs and stages that GitLab Runner executes.

When you push code to your GitLab repository, GitLab looks for this file at the root of your project and uses it to decide how to run your builds, tests, deployments, etc.

---

🧱 2. Core Components of .gitlab-ci.yml

✅ A. Jobs

A job is a single task that GitLab Runner executes, like compiling code, running tests, or deploying an app.

Example:

build-job:
  script:
    - echo "Compiling the app..."
    - make build

• build-job is the name of the job.

• script contains the shell commands the runner will execute.

Key Keywords in Jobs:

Key	Description
script	Mandatory. Shell commands to run.
stage	Stage to which the job belongs (default: test).
only / except	Specify conditions to include/exclude a job (deprecated in favor of rules).
rules	More powerful way to conditionally run jobs.
tags	Used to select a specific runner.
artifacts	What files to pass between jobs or save from the job.
cache	Used to cache dependencies between pipelines.
when	Can be on_success, manual, always, etc.
dependencies	Used to pass artifacts from previous jobs.
needs	For defining DAG-like relationships between jobs.

---

🏗️ B. Stages

Stages define the order in which jobs run.

stages:
  - build
  - test
  - deploy

Jobs in the same stage run in parallel (if runners are available), and stages run sequentially.

---

🔁 C. Workflow & Rules

workflow defines when a pipeline should be created.

workflow:
  rules:
    - if: '$CI_COMMIT_BRANCH == "main"'

• Useful to control pipeline creation based on branch, tags, or variables.

rules within jobs help define whether a job runs under certain conditions.

---

📦 D. Artifacts and Cache

• Artifacts: Persist after the job and are downloadable.

• Cache: Speeds up pipelines by reusing dependencies (like node_modules or .gradle/).

build-job:
  script: ...
  artifacts:
    paths:
      - build/
    expire_in: 1 week

  cache:
    key: ${CI_COMMIT_REF_SLUG}
    paths:
      - .gradle/

---

🧩 E. Includes

You can modularize CI by using include.

include:
  - local: 'ci/templates/deploy.yml'
  - remote: 'https://example.com/gitlab-ci-template.yml'

• Promotes reusability.

• GitLab maintains a lot of official CI templates.

---

🧪 F. Services

If your job needs a database, browser, or another service, you can spin up Docker services:

test:
  image: node:14
  services:
    - postgres:latest
  script:
    - npm test

---

📁 G. Image

Use Docker images to define the environment.

job1:
  image: python:3.9
  script:
    - python myscript.py

---

🧬 3. Sample End-to-End .gitlab-ci.yml

stages:
  - build
  - test
  - deploy

build-job:
  stage: build
  script:
    - echo "Building the app..."
    - make build
  artifacts:
    paths:
      - build/

test-job:
  stage: test
  script:
    - echo "Running tests..."
    - make test
  needs: [build-job]

deploy-job:
  stage: deploy
  script:
    - echo "Deploying..."
    - make deploy
  only:
    - main

---

🚦 4. What is Nestor?

As of now, GitLab doesn’t have a built-in feature called "Nestor" officially. However, there are three possibilities you might be referring to:

➤ A. Nestor (Third-party CI/CD Tool)

A third-party tool named "Nestor" exists that enhances GitLab CI/CD observability, often used for:

• Visualizing pipelines

• Annotating stages/jobs

• Giving analytics about pipelines

If your team has integrated it, it may appear like an add-on or plugin that monitors .gitlab-ci.yml usage.

➤ B. Internal Codename

Some teams use “Nestor” as a codename for their internal CI/CD helper tool or abstraction layer over GitLab pipelines.

➤ C. Misunderstanding of "Runner" or "Executor"

You might mean:

• GitLab Runner = Agent that runs your jobs.

• Executor = The environment (e.g., Shell, Docker) where jobs are executed.

If you can clarify "Nestor" from your context (plugin, tool, script, etc.), I’ll help further.

---

🧠 5. Summary: Common Concepts in Table

Concept	Description
Job	Defines a single task
Stage	Groups jobs in execution order
Script	Commands that are run
Image	Docker image used for job
Services	Extra containers like DBs
Artifacts	Output files of a job
Cache	Files reused between pipelines
Rules	Conditions to run a job or pipeline
Includes	Import other YAML templates
Workflow	Controls whether the pipeline is created
Runner	Agent that executes jobs

---

Would you like:

• A visual diagram of how GitLab CI/CD works?

• Help writing your own .gitlab-ci.yml?

• Or information about GitLab runners and installation?

Let me know and I’ll customize it further.