In the system, it introduces how to actually deploy a K8S After the project , As the last article in this series , Let's see Kubernetes Cluster content overview , Then summarize some deeper functions .

 

Kubernetes The overview

Here is a k8s Overview structure and content of

You can see that among the functional modules mentioned in the figure , There are others that do not appear in this article ：

l  ConfigMap

Used to store user profile definitions , Through its internal Volume Projection technology implementation , Actually, too. Volume A way to mount . This method can not only realize the reuse of applications , Moreover, more flexible functions can be realized through different configurations . When creating a container , Users can package the application as a container image , Configuration injection is performed through environment variables or external mount files .

 

l  Secret

Secret Object types are used to hold sensitive information , For example, password 、OAuth Token and SSH secret key . Put this information in Secret Put the middle ratio in Pod The definition of 、 In the container image 、 be relative to ConfigMap Say safer and more flexible . Secret It's standard k8s Resource objects , Usage and ConfigMap Very similar . At the same time, we can Secret Access control , Prevent confidential data from being accessed

l  PV

PVC yes Kubernetes Implementation of persistent data volume in , It is StatefulSet Core functions , It's also Pod The necessary means of persistence ,Kubernetes adopt PV and PVC Split , So as to achieve the decoupling of function points .

In addition to what is mentioned in the text , Kubernetes The content of clusters is also much more complex than what we have seen so far , There is also a lot of content waiting for us to explore .

ad locum , Let's summarize these deep-seated functions , It's also a for in-depth learning Kubernetes The carding of .

Kubernetes Components

The server we usually use in the process of development （ Host machine ）, stay Kubernetes The cluster is called Node node .

At the same time Kubernetes There is one or more Master The node controls multiple host computers to realize cluster , Whole Kubernetes The core scheduling functions of are basically Master Node .

Kubernetes Its main functions are composed of five major components ：

1. kubelet： Installed in the Node Node , To control Node The container in the node is complete Kubernetes The scheduling logic of
2. ControllerManager： It is the core management component of the controller mode we mentioned above , Managed everything Kubernetes Controller logic in the cluster
3. API Server： The service handles the... In the cluster api request , We've been writing kubectl, It's actually sent to API Server Request , Requests are processed and forwarded internally
4. Scheduler： be responsible for Kubernetes Service scheduling , For example, the controller just controls Pod Arrangement of , The final scheduling logic is composed of Scheduler Completed and sent a request to kubelet Executive
5. Etcd： This is a distributed database storage project , from CoreOS Development , Was eventually RedHat Acquisition becomes Kubernetes Part of , It contains Kubernetes All configuration information in the cluster , For example, all cluster objects name,IP,secret,configMap And so on , Relying on its own consistency algorithm, it can ensure the rapid and stable return of various configuration information in the system , So this is also Kubernetes And the core components in your heart

Customized functions

In addition to various powerful component functions ,Kubernetes It also provides users with a very high degree of freedom .

In order to achieve this high degree of freedom ,Kubernetes Three open interfaces are provided to users , Namely ：

l  CNI（Container Networking Interface, Container network interface ）： It is defined. Kubernetes The link mode of all networks in the cluster , The network of the whole cluster is realized through this interface . As long as the network plug-in realizes all functions in this interface , Can be used as Kubernetes Network configuration plug-in for cluster , It includes the host routing table configuration 、7 Layer network discovery 、 Packet forwarding and so on have all kinds of small plug-ins , These small plug-ins can also be used together at will , Users can customize these functions freely according to their own needs

l  CSI（Container Storage Interface, Container storage interface ） Defines some specifications for cluster persistence , As long as the storage function of this interface is implemented , Can be used as Kubernetes Persistence plug-ins l  CRI（Container Runtime Interface, Container runtime interface ）： stay Kubernetes When the container is running , For example, the default configuration Docker When the container of this cluster runs , Users are free to choose any other container project that implements this interface , Like I mentioned before containerd and rkt

Here's an interesting point ：CRI.

Kubernetes The default container for is Docker, However, due to the competition in the early stage of the project ,Docker It's not enough Kubernetes Defined by the CRI standard , Then what shall I do? ？

To solve this problem ,Kubernetes Specially for Docker Wrote a program called DockerShim The components of , namely Docker shim , Used to handle CRI Request specification , Convert into Docker operation Linux Of OCI standard （ Yes , It's the one mentioned in the second part OCI The foundation's code ）. But this function has always been by Kubernetes Project maintenance , as long as Docker New features have been released Kubernetes We have to maintain this DockerShim Components .

therefore , This recent news ——Kubernetes Will be in next year's version v1.20 Delete... From DockerShim Components , It means starting with the new version next year ,Kubernetes Will not fully support Docker Container update .

But in fact, this may not have any impact on our ordinary developers , The worst result is that our image needs to be from Docker Change to something else Kubernetes Supported container images .

However, according to the news released by various cloud platforms during this period , These platforms will provide corresponding conversion measures , For example, we still provide Docker Mirror image , The platform will convert these images into other images when publishing operation and maintenance ; Or these platforms will maintain a DockerShim To support Docker, There are solutions .

Architecture Overview and summary

In this part, let's take a look at Kubernetes The architecture of the figure ：

Through this series of learning , As an ordinary programmer , Have to admire Google Have a deep and extreme understanding of coding , There are too many components in the framework just because of decoupling , And it also provides such a large degree of freedom , It has to be said that it is a framework with great technical depth encountered by our movable type development team in the process of learning .

But this high degree of freedom also has negative effects .

During deployment ,Kubernetes Cluster complexity is very high , Deploy a to meet the needs of the production environment Kubernetes The framework is even more difficult , There are also special sellers on the Internet Kubernetes Script program for cluster deployment in production environment , so Kubernetes The scale of the system .

In the process of learning, you can use kinD perhaps minikube In local with Docker In the form of a Kubernetes colony , However, there is still a certain gap between this level of learning and the production environment .

summary

This series of articles , It describes in detail several difficult gods encountered by our movable type lattice development team in the process of going to heaven .

From the development of cloud platform to k8s Specific use of , Step by step, I explained a cloud platform , From the original virtual machine , To PaaS embryonic form , To Docker Containerization , And finally Kubernetes The transition and evolution of the form of .

Human memory needs to rely on precursor nodes , Just through an article, I want to put Kubernetes It is obviously impossible to explain the technical points and various difficult to remember nouns one by one , Our idea is to let everyone understand the evolution process of the whole cloud ecology step by step , So as to finally understand the whole project .

Finally, I want to give you a word ：

It's on paper , We must know that we must do it .

After our development team members read these documents for the first time, they feel that they have completely mastered , But in the actual document writing process , I found that my eyes were black , I don't know where to start .

Too many knowledge points only stay in heard of , Just know what stage it is . I suggest you start here , Try the examples mentioned in the article , We believe that after writing it ourselves , You will have a different understanding of these contents .

Although this series is over , However, in the follow-up content, we will continue to tell you more about various technical secrets encountered by new and old grapes in the grape city 、 Share .

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