# Scheduler 扩展

如果默认的调度器不满足要求，还可以部署自定义的调度器。并且，在整个集群中还可以同时运行多个调度器实例，通过 `pod.Spec.schedulerName` 来选择使用哪一个调度器（默认使用内置的调度器）。

## 开发自定义调度器

自定义调度器主要的功能是查询未调度的 Pod，按照自定义的调度策略选择新的 Node，并将其更新到 Pod 的 Node Binding 上。

比如，一个最简单的调度器可以用 shell 来编写（假设已经启动 `kubectl proxy` 并监听在 `localhost:8001`）：

```bash
#!/bin/bash
SERVER='localhost:8001'
while true;
do
    for PODNAME in $(kubectl --server $SERVER get pods -o json | jq '.items[] | select(.spec.schedulerName =="my-scheduler") | select(.spec.nodeName == null) | .metadata.name' | tr -d '"')
;
    do
        NODES=($(kubectl --server $SERVER get nodes -o json | jq '.items[].metadata.name' | tr -d '"'))
        NUMNODES=${#NODES[@]}
        CHOSEN=${NODES[$[ $RANDOM % $NUMNODES]]}
        curl --header "Content-Type:application/json" --request POST --data '{"apiVersion":"v1","kind":"Binding","metadata": {"name":"'$PODNAME'"},"target": {"apiVersion":"v1","kind"
: "Node", "name": "'$CHOSEN'"}}' http://$SERVER/api/v1/namespaces/default/pods/$PODNAME/binding/
        echo "Assigned $PODNAME to $CHOSEN"
    done
    sleep 1
done
```

## 使用自定义调度器

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  # 选择使用自定义调度器 my-scheduler
  schedulerName: my-scheduler
  containers:
  - name: nginx
    image: nginx:1.10
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://kubernetes.feisky.xyz/extension/scheduler.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.