kubernetes-handbook/practice/helm.md

# 使用Helm管理kubernetes应用

Helm是一个kubernetes应用的包管理工具，用来管理[charts](https://github.com/kubernetes/charts)——预先配置好的安装包资源，有点类似于Ubuntu的APT和CentOS中的yum。

Helm chart是用来封装kubernetes原生应用程序的yaml文件，可以在你部署应用的时候自定义应用程序的一些metadata，便与应用程序的分发。

Helm和charts的主要作用：

- 应用程序封装
- 版本管理
- 依赖检查
- 便于应用程序分发

## 安装Helm

**前提要求**

Kubernetes1.5以上版本，集群可访问到的镜像仓库。

首先需要安装helm客户端

```bash
curl https://raw.githubusercontent.com/kubernetes/helm/master/scripts/get > get_helm.sh
chmod 700 get_helm.sh
./get_helm.sh
```

创建tiller的`serviceaccount`和`clusterrolebinding`

```bash
kubectl create serviceaccount --namespace kube-system tiller
kubectl create clusterrolebinding tiller-cluster-rule --clusterrole=cluster-admin --serviceaccount=kube-system:tiller
```

然后安装helm服务端tiller

```bash
helm init -i sz-pg-oam-docker-hub-001.tendcloud.com/library/kubernetes-helm-tiller:v2.3.1
```

我们使用`-i`指定自己的镜像，因为官方的镜像因为某些原因无法拉取。

为应用程序设置`serviceAccount`：

```bash
kubectl patch deploy --namespace kube-system tiller-deploy -p '{"spec":{"template":{"spec":{"serviceAccount":"tiller"}}}}'
```

检查是否安装成功：

```bash
$ kubectl -n kube-system get pods|grep tiller
tiller-deploy-2372561459-f6p0z         1/1       Running   0          1h
$ helm version
Client: &version.Version{SemVer:"v2.3.1", GitCommit:"32562a3040bb5ca690339b9840b6f60f8ce25da4", GitTreeState:"clean"}
Server: &version.Version{SemVer:"v2.3.1", GitCommit:"32562a3040bb5ca690339b9840b6f60f8ce25da4", GitTreeState:"clean"}
```

## 创建自己的chart

我们创建一个名为`mychart`的chart，看一看chart的文件结构。

```bash
$ helm create mongodb
$ tree mongodb
mongodb
├── Chart.yaml
├── charts
├── templates
│   ├── NOTES.txt
│   ├── _helpers.tpl
│   ├── deployment.yaml
│   └── service.yaml
└── values.yaml

2 directories, 6 files
```

### 模板

`Templates`目录下是yaml文件的模板，遵循[Go template](https://golang.org/pkg/text/template/)语法。使用过[Hugo](https://gohugo.io)的静态网站生成工具的人应该对此很熟悉。

我们查看下`deployment.yaml`文件的内容。

```yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: {{ template "fullname" . }}
  labels:
    chart: "{{ .Chart.Name }}-{{ .Chart.Version | replace "+" "_" }}"
spec:
  replicas: {{ .Values.replicaCount }}
  template:
    metadata:
      labels:
        app: {{ template "fullname" . }}
    spec:
      containers:
      - name: {{ .Chart.Name }}
        image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
        imagePullPolicy: {{ .Values.image.pullPolicy }}
        ports:
        - containerPort: {{ .Values.service.internalPort }}
        livenessProbe:
          httpGet:
            path: /
            port: {{ .Values.service.internalPort }}
        readinessProbe:
          httpGet:
            path: /
            port: {{ .Values.service.internalPort }}
        resources:
{{ toYaml .Values.resources | indent 12 }}
```

这是该应用的Deployment的yaml配置文件，其中的双大括号包扩起来的部分是Go template，其中的Values是在`values.yaml`文件中定义的：

```Yaml
# Default values for mychart.
# This is a YAML-formatted file.
# Declare variables to be passed into your templates.
replicaCount: 1
image:
  repository: nginx
  tag: stable
  pullPolicy: IfNotPresent
service:
  name: nginx
  type: ClusterIP
  externalPort: 80
  internalPort: 80
resources:
  limits:
    cpu: 100m
    memory: 128Mi
  requests:
    cpu: 100m
    memory: 128Mi
```

比如在`Deployment.yaml`中定义的容器镜像`image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"`其中的：

- `.Values.image.repository`就是nginx
- `.Values.image.tag`就是stable

以上两个变量值是在create chart的时候自动生成的默认值。

### 检查配置和模板是否有效

当使用kubernetes部署应用的时候实际上讲templates渲染成最终的kubernetes能够识别的yaml格式。

使用`helm install --dry-run --debug <chart_dir>`命令来验证chart配置。该输出中包含了模板的变量配置与最终渲染的yaml文件。

```bash
$ helm install --dry-run --debug mychart
Created tunnel using local port: '58406'
SERVER: "localhost:58406"
CHART PATH: /Users/jimmy/Workspace/github/bitnami/charts/incubator/mean/charts/mychart
NAME:   named-jackal
REVISION: 1
RELEASED: Tue Oct 24 18:57:13 2017
CHART: mychart-0.1.0
USER-SUPPLIED VALUES:
{}

COMPUTED VALUES:
image:
  pullPolicy: IfNotPresent
  repository: nginx
  tag: stable
replicaCount: 1
resources:
  limits:
    cpu: 100m
    memory: 128Mi
  requests:
    cpu: 100m
    memory: 128Mi
service:
  externalPort: 80
  internalPort: 80
  name: nginx
  type: ClusterIP

HOOKS:
MANIFEST:

---
# Source: mychart/templates/service.yaml
apiVersion: v1
kind: Service
metadata:
  name: named-jackal-mychart
  labels:
    chart: "mychart-0.1.0"
spec:
  type: ClusterIP
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: nginx
  selector:
    app: named-jackal-mychart

---
# Source: mychart/templates/deployment.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: named-jackal-mychart
  labels:
    chart: "mychart-0.1.0"
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: named-jackal-mychart
    spec:
      containers:
      - name: mychart
        image: "nginx:stable"
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 80
        livenessProbe:
          httpGet:
            path: /
            port: 80
        readinessProbe:
          httpGet:
            path: /
            port: 80
        resources:
            limits:
              cpu: 100m
              memory: 128Mi
            requests:
              cpu: 100m
              memory: 128Mi
```

## 部署todo测试案例

```bash
$ git clone https://github.com/bitnami/charts.git
$ cd charts/incubator/mean
$ helm dep list
NAME   	VERSION	REPOSITORY                                       	STATUS
mongodb	0.4.x  	https://kubernetes-charts.storage.googleapis.com/	missing
```

缺少mongodb的依赖，需要更新一下chart。

```bash
$ helm dep update
Hang tight while we grab the latest from your chart repositories...
...Unable to get an update from the "local" chart repository (http://127.0.0.1:8879/charts):
	Get http://127.0.0.1:8879/charts/index.yaml: dial tcp 127.0.0.1:8879: getsockopt: connection refused
...Successfully got an update from the "stable" chart repository
Update Complete. ⎈Happy Helming!⎈
Saving 1 charts
Downloading mongodb from repo https://kubernetes-charts.storage.googleapis.com/
```

所有的image都在 `values.yaml` 文件中配置。

下载缺失的chart。

```bash
$ helm dep build
Hang tight while we grab the latest from your chart repositories...
...Unable to get an update from the "local" chart repository (http://127.0.0.1:8879/charts):
	Get http://127.0.0.1:8879/charts/index.yaml: dial tcp 127.0.0.1:8879: getsockopt: connection refused
...Successfully got an update from the "stable" chart repository
Update Complete. ⎈Happy Helming!⎈
Saving 1 charts
Downloading mongodb from repo https://kubernetes-charts.storage.googleapis.com/
```

## 参考

- [Deploy, Scale And Upgrade An Application On Kubernetes With Helm](https://docs.bitnami.com/kubernetes/how-to/deploy-application-kubernetes-helm/)
- [Helm charts](https://github.com/kubernetes/helm/blob/master/docs/charts.md)
- [Go template](https://golang.org/pkg/text/template/)
- [How To Create Your First Helm Chart](https://docs.bitnami.com/kubernetes/how-to/create-your-first-helm-chart/)