# K8s 在 DevOps 中的作用

### DevOps

**Development + Operation ＝ DevOps，Dev: 開發部門，Ops ＝ 維運部門 。**

\[1]在傳統的軟體開發流程，往往是Dev speed > Ops speed 而造成一種gap，很可能在整個軟體發中，因為整體 Release Version 速度慢，以致難以去驗證功能的市場性，造成產能的過度浪費，常常開發出無用的功能。

DevOps 主要有五個階段：

1. Continuous Planning: 指的是透過使用者回饋或者其他部門帶來的需求。
2. Continuous Development: 指的是開發工程師持續的將需求完成，並完成建制。
3. Continuous Testing: 指的是開發好的 Image 自動的進行測試。
4. Continuous Integration: 將測試好的功能發版本並部屬上產品。
5. Continuous Monitoring: 持續的監測產品營運的狀況，持續的提出優化的需求

可參考下圖示例：

![](/files/mffqIUiA9ssDiyanY4u3)

K8s 的出現主要目的是解決Operation 上Continuous Integration、Continuous Monitoring 的問題，一般來說透過Git Repository  工具上的 CI/CD 工具，當工程師Push Code 時，將自動的執行所有的測試，並觸發K8s 工具，使的Code 可以更快速的反應在產品端。

### DevOps Pipeline

\[2]為了推行DevOps加速整個產品的開發週期，會由Dev與Ops 部門一起制訂出開發的Pipeline，盡量讓每一站點都可以自動化，一般來說是會由DevOps 工程師與Dev、QA一起制訂出來。下圖為一般pipeline 會制定的Pipeline，一般會經歷過幾個階段:

1. push code: Dev 工程師將程式碼發布到Repo 上
2. Build: 程式碼將經歷過 code 品質的測試，ex: lint，再來會經過unit test 
3. MR: Merge Request 這是唯一需要人工的步驟，由Code Reviewer 去審核且合併到Branch 上
4. Deploy: 指的是將build 階段的產物，發布到正式或者測試環境中
5. E2E Test: End to End Test 指的是直接透過終端的操作，整合測試功能
6. Monitoring: 正式發布後，持續的紀錄系統的 Log

下圖為Pipeline 流程圖：

![](/files/rQnXrXOA5gJ3mDY57tmf)

### GitOps

\[3]GitOps 是一個在Git Repository 上實現自動化更新K8s Cluster 的方式，透過Git CI/CD 進行自動化測試之後並把成功build 好的 image 傳入Image Registry 中並Trigger K8s 更新Deployment，如下圖所示。簡單來說GitOps 某種程度上減輕了Ops 許多的工作，讓開發之後自動的進行一系列的Ops，減輕原有Ops部門與Dev部門的溝通成本。

![](/files/aaPDOYxY3XlKF9OplyyD)

#### GitLab GitOps

在GitLab 中要做到GitOps 其實複雜蠻多的，首先要先具備2種Gitlab Runner:

1. Docker gitlab-runner: 使得Repo 可以進行 Unit test 和 build image 等功能。
2. K8s gitlab- runner:  使得Repo可以進行觸發進行dev 的環境部屬，建制Dev、Production 的環境

**Install Docker gitlab-runner**

* Prepare git-lab-runner config

```toml
concurrent = 1
check_interval = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "raspberry pi"
  url = "https://gitlab.com/"
  token = <Token>
  executor = "docker"
  [runners.custom_build_dir]
  [runners.cache]
    [runners.cache.s3]
    [runners.cache.gcs]
    [runners.cache.azure]
  [runners.docker]
    tls_verify = false
    image = "docker:latest"
    privileged = true  // MUST
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache", "/certs/client"] // MUST
    shm_size = 0
```

* 需要包含docker in docker 的功能，為了可以 build container image 並上傳於container registry 中

```shell
docker volume create gitlab-runner-config

docker run -d --name gitlab-runner --restart always  \
   -v /var/run/docker.sock:/var/run/docker.sock  \
   -v gitlab-runner-config:/etc/gitlab-runner \
   gitlab/gitlab-runner:latest
```

**Install GitLab Agent**

* Install k3s

```shell
curl -sfL https://get.k3s.io | INSTALL_K3S_CHANNEL=latest sh -
```

* At default branch add `config.yaml` :  內容可為空。

```shell
echo "" > .gitlab/agents/<FOLDER NAME>/config.yaml  
```

* 去Repo 的 infrastructure 新增Agent， 參考<https://www.youtube.com/watch?v=XuBpKtsgGkE>

**Install GitLab Runner**

* prepare helm
* prepare `runner-chart-values.yaml`

```yaml

gitlabUrl: https://gitlab.com/
runnerRegistrationToken: <YOUR TOKEN>
rbac:
    create: true
runners:
    privileged: true
```

* Install Runner

```shell
sudo helm --kubeconfig /etc/rancher/k3s/k3s.yaml \
    install --namespace gitlab-cd gitlab-runner \
    -f runner-chart-values.yaml gitlab/gitlab-runner
```

{% hint style="info" %}
The manipulations of gitlab-runner will not roll back status after running cmds.
{% endhint %}

### 參考資料

\[1] Virmani, Manish. "Understanding DevOps & bridging the gap from continuous integration to continuous delivery." *Fifth international conference on the innovative computing technology (intech 2015)*. IEEE, 2015.\
\[2] Ivanov, Vitalii, and Kari Smolander. "Implementation of a DevOps pipeline for serverless applications." *International conference on product-focused software process improvement*. Springer, Cham, 2018.\
\[3] Beetz, Florian, and Simon Harrer. "GitOps: The Evolution of DevOps?." *IEEE Software* (2021).


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