---
tags: 1082, lsa
---
- Book mode https://hackmd.io/@ncnu-opensource/book

About csgroup & namespace
===
[TOC]
## Q1：cgroup & namespace 的實際差別與相互關係？
### Answer
- 每個 Container 可能都有自己的 cgroup namespace 與 net namespace 等等，藉以區分不同的 Container，host 也有自己的 cgroup
- 建議搭配文件 [CHAPTER 81. UNDERSTANDING CONTROL GROUPS
| Red Hat](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/system_design_guide/understanding-control-groups_setting-limits-for-applications) 查看 `cgroup` 定義，及參考 [CHAPTER 82. WHAT KERNEL RESOURCE CONTROLLERS ARE | Red Hat](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/system_design_guide/what-kernel-resource-controllers-are_setting-limits-for-applications) 瞭解 Linux 是透過哪些 conroller 管理其 CPU/Memory/IO/Network resources。

### 額外補充：

- Cgroups：limit how much you can use
- Resourse metering and limiting
- memory
- CPU
- block I/O
- **network**
- Device node (/dev/*) access control
- Namespace：limit what you can see (and therefore use)
- provide processes with their own view of system
- Multiple namespcaes:
- pid
- net
- mnt
- uts
- ipc
- user
- Each process is in one namespace of each type

### Example:


## Q2：有沒有可能讓 Container 共用 IP

### Answer

- 可以
- 可以先開啟一台 container 此時會分配給他一個 IP，接著開一個沒有 IP 的 container(可以在建立時設 net)，將沒有 IP 的 container link 到有 IP 的 container 的 namespace (或許可以在剛開始開啟時設定，但要查 command 參數)

## Q3：k8s Container 間可以用 localhost 互相訪問，Why？

- web 可以直接用 `localhost:3306` 訪問 DB，Why？

### Answer

- 由於他們共用 `namespace`，並且一個 pod 內部只有一個 ip，旁邊可能會有 `pause container` 負責 link (k8s 處理) 內部其餘 container

## Q4： k8s 簡易架構圖

- 想快速瞭解 k8s 可參考 [Load balancing and scaling long-lived connections in Kubernetes
](https://learnk8s.io/kubernetes-long-lived-connections)

## Reference

1. [CHAPTER 81. UNDERSTANDING CONTROL GROUPS
| Red Hat](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/system_design_guide/understanding-control-groups_setting-limits-for-applications)
1. [CHAPTER 82. WHAT KERNEL RESOURCE CONTROLLERS ARE | Red Hat](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/system_design_guide/what-kernel-resource-controllers-are_setting-limits-for-applications)
1. [namespace | Linux man-page](https://www.man7.org/linux/man-pages/man7/namespaces.7.html)
1. [Linux namespaces(wiki)](https://en.wikipedia.org/wiki/Linux_namespaces#Network_(net))
1. [Containers：cgroups, Linux kernel namespaces, ufs, Docker, and intro to Kubernetes pods](https://www.youtube.com/watch？v=el7768BNUPw)
1. [The Almighty Pause Container
](https://www.ianlewis.org/en/almighty-pause-container)
1. [Pods | Kubernetes](https://kubernetes.io/docs/concepts/workloads/pods/pod/)
1. [Docking A Docker Container — Part 2 ：Namespace, cgroup](https://medium.com/@tomdeore/docking-a-docker-container-part-2-c1206e7c6677)
1. [Load balancing and scaling long-lived connections in Kubernetes](https://learnk8s.io/kubernetes-long-lived-connections)