# Lesson 3: OCI Compute Services

## Bare Metal 裸机

A physical server without any virtualization, you have to set up a virtualization layer, then you have to manage all the things: OS, run-times etc. Oracle offer a off-box virtualization**1**

### Uses cases

Direct Hardware Access with all the Security, Capabilities, Elasticity and Scalability of OCI.

* Workloads that are performance-intensive

  性能密集型工作负载
* Workloads that are not virtualized
* Workloads that require a specific hypervisor
* Workloads that require BYOL (Bring Your Own Licensing)

## Dedicated Virtual Hosts 专用虚拟主机

A host server, It has a virtualization, you can run VMs on top of that.

## Virtual Machines

A virtual machine is a guest on a host server with hypervisor based virtualization.

### Use cases

VMs require work - OS path management, security configuration, monitoring, application configuration and scaling to handle variable traffic, if you want to:

* control all aspects of an environment
* deploy a legacy app running on Windows or Linux
* **move applications from on-premises to OCI**

## Container Engine

you are managing your code, and then of course you are managing your App container**2**.

## Functions

Oracle Functions where you just write the code. You write the code in different languages, and you don't worry about any of the underlying infrastructure.

* small but powerful blocks of code 
* stored as Docker images in a specified Docker registry.
* invoked in response to a CLI command or signed HTTP request (为了响应CLI命令或签名的HTTP请求而调用)

## Instance basics

Compute instances depend on other OCI services such as Block Volume and Virtual Cloud Network (VCN)

![](https://imgur.com/zrghb9s.png)

## Vertical Scaling

Scale-up and Scale-down instance shape (实例外形) supported, the instance must be stopped before resize it.

## Autoscaling

Which is literally horizontal scaling. Enables **large scale deployment** of VMs from a single gold image with automatic configuration, referred to as Scale-out or Scale-in.

![](https://imgur.com/YbKBZMG.png)

### How to autoscaling

![How to autoscaling](https://imgur.com/SZ5sl1f.png)

1. You have an instance running --> what you do is create **a configuration**. The configuration is nothing but an operating system image, your metadata, storage disks, all that stuff. It basically earns about what you instance looks like. You're creating this thing called a *gold image* here.
2. The take this configuration and you create what is called an **instance pool** and as you can see here, instead of one instance, now we have two. And you could do many more.
3. Put these instances in different ADs. Then define your **scaling rules** to manage hundreds of VMs together as one unit.

## VM vs Container

There were some downsides to VM, you were **repeating the operating system** everywhere. And so these became **bulky** (笨重的). For example if you have 10 VMs, basically you're packaging the operating system 10 times.

The concept of containers where we raised the abstraction one more level, and now we **abstract/virtualize** the **operating system**. It **shares** the **kernel** or the **operating system** with other containers.

![](https://imgur.com/ZIPLBR8.png)

**1:** **off-box virtualization:** we off-load network and storage to a separate hardware card in the server. People also call it as custom silicon. 我们把网络和储存卸货到一个单独的硬件卡上.

**2 :** **App container:** is a container runtime which executes container and manages container images on a node. The most widely, known app container or container runtime is Docker.


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