# GitLab

## What is GitLab?

[GitLab](https://docs.gitlab.com/ee/) is a version-controlled (git) platform for hosting code in repositories. We can define CI/CD pipelines (e.g., `.gitlab-ci.yml` ) to automate things like code scanning and deployment. 

## .gitlab-ci.yml

This is the configuration file used to define CI/CD jobs for your pipeline. The configuration file gets written in YAML and a syntax reference can be found on the [official GitLab docs](https://docs.gitlab.com/ee/ci/yaml/index.html).

For reference, I have a fully functional [file hosted here](https://github.com/Ty182/AWS-Cloud-Resume-Challenge/blob/main/.gitlab-ci.yml) for a past project I developed. Let's break down some of the keywords.

### Stages

> Stages is where we define the names and order of the pipeline stages.

Here I have two stages shown and each runs jobs. For example, the `security_scan` stage runs the security code scanning job. The other runs a job that ensures my terraform code is valid. 

```yaml
stages:
    - security_scan
    - validate
```

### Variables

> Variables is where we define any variables needed throughout the pipeline.

Here I have a few. When needed throughout my code, I can simply use `WEB_S3` (or any other variable) instead of writing out the full name. This makes it super easy to change the name in a single place rather than updating multiple places in the code. 

```yaml
variables:
  TF_ROOT: "$CI_PROJECT_DIR/terraforms"
  WEB_DIR: "$CI_PROJECT_DIR/assets"
  WEB_S3: "tylerpettycloudresumechallenge.com"
```

### Jobs

> Jobs get defined and execute commands. For example, the job shown below is called `deploy`. It gets run as part of the stage, `stage: deploy` (I purposely gave it the same name for simplicity). 

This job does a few things, 

1. `script` lets us execute shell commands on the runner (the container).
   * Two terraform commands get run
2. `when` let's us define when this job gets run.
   * `manual` means I initiate this job in the console by clicking a button
3. `allow_failure` determines whether a job can fail or not
   * `false` means if the job fails, subsequent jobs cannot run
   * `true` lets subsequent jobs run despite this job failing
4. `rules` define conditions that must be met to run this job
   * `if: $CI_COMMIT_BRANCH == "main"` means only run this job if the code is being committed to a branch called `main`

```yaml
deploy:
  stage: deploy
  script:
    - terraform init
    - terraform apply plan
  when: manual
  allow_failure: false
  rules:
    - if: $CI_COMMIT_BRANCH == "main"
```