> For the complete documentation index, see [llms.txt](https://ysfang82.gitbook.io/development-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ysfang82.gitbook.io/development-notes/aws-notes/service/compute-and-load-balancing/ec2.md).

# EC2

**Introduction**

* Elastic Compute Cloud (EC2) is a web service that provides resizable compute capacity.
* Different types of EC2 instance for multiple usage.
  * D: Density Storage (Fileserver, Data Warehousing, Hadoop)
  * R: Ram 
  * M: main choice for general purpose
  * C: Compute
  * G: Graphics
  * I: IOPS (NoSQL DBs, Data Warehousing)
  * F: FPGA (Field Programmable Gate Array, hardware acceleration)
  * T: Cheap general purpose
  * P: Graphics, General purpose of GPU (Machine Learning, Bit coin mining)
  * X: Extreme Memory (SAP HANA, Apache Spark)
* EC2 instance Options:
  * On demand
    * Pay by the second so far
  * Reserved Instance (RI)
    * Have a discount but for consistent usage in 1 \~ 3 years.
    * Types of RI (can be either regional / zonal):
      * Standard RI (Up to 75% off on demand)
        * Cannot modify Instance Family (Ex. `m5.2xlarge`, `m5` is the Instance Family.)
        * Can be sold
      * Convertible RI (Up to 54% off on demand)
        * Can modify Instance Family
        * Can not be sold
      * [Scheduled RI](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-scheduled-instances.html)
  * Spot
    * To bid whatever price for the instance capacity. Suitable for flexible start and end times application with very low prices (can be 90% off compared to On-demand).
    * If instance terminated manually, cost of the hour is charged. If instance terminated by AWS, cost of the hour is free.
  * Dedicated Instances:
    * No other customers will share your hardware.
  * Dedicated Hosts
    * Physical EC2 server. Suitable for some applications need instance lock-in.
    * Great for software licenses that operate the core, or CPU socket level.
    * Can define host affinity so that instance reboots are kept on the same host.

**Feature**

* Security Group
  * To set up allow rules (not deny rules)
  * Many to many relationship to EC2.
  * Default SG allows all inbound / outbound, Manually created Security Groups allow no traffic by default.
  * SG rule is stateful.
* Placement Groups
  * A strategy to congrol EC2 instance placement
  * Strtegies:
    * Cluster: instances in one AZ for high latency (10 Gbps).
    * Partition: instances in different logical partition. Good for distributed services like Hadoop, Cassandra, Kafka. Up to 7 partitions per AZ, up to 100s of EC2 instances per partition.
    * Spread: instances in different physical rack and in different AZs. Good for critical applications. Limited to 7 instances per placement group.
  * Can move instance into / out of a placement group **without termination** (**stop** the instance, CLI to move, restart instance).
* Termination protection is off by default, can be anabled.
* PEM Key scenarios
  * Migrate instance to another region with the same PEM key
    * Copy the AMI of your EC2 machine to new region and start up an instance using the AMI.
      * Choose the "Proceed without a keypair" when launching the instance
      * Or import the **public** **key**
    * The PEM key is regional
  * When key is stolen
    * Terminate the instance 
    * Launch new instance with another SSH key pair
  * Replace a PEM key
    * log in to the instance and update the public key in `~/.ssh/authorized_keys`
    * Users can only select an SSH key pair when they launch a new instance.
* EC2 included metrics:
  * CPU: CPU Utilization + Credit Usage / Balance
  * Network: Network In / Out
  * Status Check: 
    * Instance status: check EC2 VM
    * System status: check the underlying hardware
  * Disk: Read / Write for Ops / Bytes (only for instance store)
  * **RAM is NOT included in AWS EC2 metrics (must create a custom metric).**
* [Hibernation Limit](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/Hibernate.html)
  * Enable the hibernation feature on the Configure Instance Details page
  * AMI: Linux, Ubuntu
  * EBS with enough space to save RAM data
  * Not compatible with ASG / ECS 

**CLI**

* Fetching EC2 meta-data
  * Link into EC2 and list all options of meta-data display

    ```
    $ curl http://169.254.169.254/latest/meta-data/
    ```
  * Displaying public ip.

    ```
    $ curl http://169.254.169.254/latest/meta-data/public-ipv4
    ```
* Configure privilege with programmatic credential of IAM\
  Run below command and give Access Key ID and Secret Access Key. The information is stored in EC2 instance so it's not secured.

  ```
    $ aws configure
  ```

  ***PS.*** A good practice is to use IAM Role to be assigned to EC2 instance (when creation or later on), instead of giving credential away (constraint with EC2 instance level).

**Trouble Shooting**

* A HTTP server in EC2 with EIP cannot be accessed from on-premise
  * Security Group should have inbound allow for port 80
  * NACL of the subnet should allow 80 for inboud, ephemeral ports for outbound.
  * The subnet of the instance should be associated with the main route table.