Kubernetes static pod (static POD)

The stack etcd colony ： There are... In a cluster 3 individual master, Every master There's... In it etcd This pod, This pod Usually by kubelet Self management .

kubelet Will read one config, This config Defined static pod path,kubelet Its function is to maintain pod Life cycle of , He has several ways to load pod List of , One way is to listen api server, Another way is that it will scan the local static pod path, Scan this directory , It needs to see if there is any pod detailed list , If any, load directly .

This pattern is etcd Will be in every master Deployment above , It is deployed statically .

Stackable benefits ：apiserver and etcd Are tightly bound , all apiserver Your request is in loopback Send to etcd, The read operation can be read directly , The read operation does not need to go through master, The read operation does not need to be called through the network , I left here , Secondly, these components are put together for management and maintenance , Data can be read without network calls . also etcd It's a heavy plate , It's right disk io There are requirements , Other applications are not so demanding , So it is also ok Of .

 

 

What is? Static Pod

static state Pod On the specified node by kubelet Daemons manage directly , Unwanted API The server regulatory . With... Managed by the control plane Pod（ for example ,Deployment） Different ;kubelet Monitor each static state Pod（ Restart after it crashes ）.

static state Pod Will always be bound to a specified node Kubelet.

kubelet Will try to pass Kubernetes API The server is for each static server Pod Automatically create a Mirror image Pod. This means that the static running on the node Pod Yes API Services are visible , But not through API Server to control . Pod The name will use the node host name starting with a hyphen as the suffix .

The most common Static Pod

• etcd
• kube-apiserver
• kube-controller-manager
• kube-scheduler

How to create Static Pod

Static files

By looking at kubelet Of service The file shows ：

Running kubelet The configured directory will be scanned regularly ( For example, in the example /etc/kubernetes/manifests Catalog ) Changes in , And according to the document / Vanished Pod To add / Delete Pod. 

Http request

kubelet Periodically from –manifest-url= Download at the address specified by the parameter ⽂ Pieces of , And translate it into Json/Yaml Format
pod Definition . Subsequent operations ⽅ Form and –pod-manifest-path= identical ,kubelet It will be downloaded again from time to time ⽂ Pieces of , When ⽂ Stop or start the static state correspondingly when the component changes pod; The process and principle are the same, so I won't introduce them in detail here .

 

 

static state Pod By kubelet There are only specific Node Upper Pod. these Pod Cannot pass API Server Conduct management , I can't go with RC、Deployment perhaps DaemonSet relation , And there is no health check , This type of Pod from kubelet Created , And only in kubelet Where Node Up operation .

Create static Pod There are two ways ：

The configuration file
HTTP
One 、 The configuration file

First, set when necessary kubelet Launch parameters “--podmainifest-path”, Or in kubelet Set... In the configuration file of staticPodPath, The specified path is kubelet Monitoring path ( If k8s Clusters are composed of kubeadm build , The default is stored in the directory /etc/kubernetes/manifests Next ),kubelet The directory will be checked regularly , And according to the yaml Document and json File to create Pod operation .

for example ： The configuration directory is /etc/kubelet.d, The configuration startup parameter is --podmainifest-path=/etc/kubelet.d, And then restart kubelet.

stay /etc/kubelet.d Devolution of the catalogue static_pod.yaml file , The contents are as follows ：

---
apiVersion: v1
kind: Pod
metadata:
    name: static-pod
    labels:
        name: static-pod
spec:
    containers:
    - name: static-pod
      image: nginx
      ports:
      - name: web
        containerPort: 80
Wait a moment , You can find that the cluster has started a pod( If it has not been started for a long time , Check the system log 、var/log/messages)

$ kubectl get pods --all-namespaces
NAMESPACE     NAME                                           READY   STATUS    RESTARTS   AGE
default       static-pod-host-192-168-100-121                1/1     Running   0          8s
The pod Can't use API Server Delete , If you try to delete it, it will make the pod be in pending state , And will never be deleted . If you want to delete this pod, Just store before yaml File directory , Delete the relevant yaml File can

Two 、HTTP The way

Same as through setting kubelet Start parameter of ‘--manifest-url’,kubelet It will be regular from this URL Address download Pod The definition file for , And yanl perhaps json File format for parsing , Then create pod, The implementation method is the same as that of the configuration file