Aggregation

API Aggregation 允许在不修改 Kubernetes 核心代码的同时扩展 Kubernetes API，即将第三方服务注册到 Kubernetes API 中，这样就可以通过 Kubernetes API 来访问外部服务。

备注：另外一种扩展 Kubernetes API 的方法是使用 CustomResourceDefinition (CRD)。

何时使用 Aggregation

满足以下条件时使用 API Aggregation	满足以下条件时使用独立 API
Your API is Declarative.	Your API does not fit the Declarative model.
You want your new types to be readable and writable using kubectl.	kubectl support is not required
You want to view your new types in a Kubernetes UI, such as dashboard, alongside built-in types.	Kubernetes UI support is not required.
You are developing a new API.	You already have a program that serves your API and works well.
You are willing to accept the format restriction that Kubernetes puts on REST resource paths, such as API Groups and Namespaces. (See the API Overview.)	You need to have specific REST paths to be compatible with an already defined REST API.
Your resources are naturally scoped to a cluster or to namespaces of a cluster.	Cluster or namespace scoped resources are a poor fit; you need control over the specifics of resource paths.
You want to reuse Kubernetes API support features.	You don’t need those features.

开启 API Aggregation

kube-apiserver 增加以下配置

--requestheader-client-ca-file=<path to aggregator CA cert>
--requestheader-allowed-names=aggregator
--requestheader-extra-headers-prefix=X-Remote-Extra-
--requestheader-group-headers=X-Remote-Group
--requestheader-username-headers=X-Remote-User
--proxy-client-cert-file=<path to aggregator proxy cert>
--proxy-client-key-file=<path to aggregator proxy key>

如果 kube-proxy 没有在 Master 上面运行，还需要配置

--enable-aggregator-routing=true

创建扩展 API

1. 确保开启 APIService API（默认开启，可用 kubectl get apiservice 命令验证）

2. 创建 RBAC 规则

3. 创建一个 namespace，用来运行扩展的 API 服务

4. 创建 CA 和证书，用于 https

5. 创建一个存储证书的 secret

6. 创建一个部署扩展 API 服务的 deployment，并使用上一步的 secret 配置证书，开启 https 服务

7. 创建一个 ClusterRole 和 ClusterRoleBinding

8. 创建一个非 namespace 的 apiservice，注意设置 spec.caBundle

9. 运行 kubectl get <resource-name>，正常应该返回 No resources found.

可以使用 apiserver-builder 工具自动化上面的步骤。

# 初始化项目
$ cd GOPATH/src/github.com/my-org/my-project
$ apiserver-boot init repo --domain <your-domain>
$ apiserver-boot init glide

# 创建资源
$ apiserver-boot create group version resource --group <group> --version <version> --kind <Kind>

# 编译
$ apiserver-boot build executables
$ apiserver-boot build docs

# 本地运行
$ apiserver-boot run local

# 集群运行
$ apiserver-boot run in-cluster --name nameofservicetorun --namespace default --image gcr.io/myrepo/myimage:mytag
$ kubectl create -f sample/<type>.yaml

示例

见 sample-apiserver 和 apiserver-builder/example。