aws: ec2: ebs and instance store

The post discusses ebs and instance store.

what is a ec2 instance
A running virtual machine in aws cloud.

instance and root device volume
Instances can be categorised into two groups according to their root device volume.

  • A ebs-backed instance is a running machine whose image is stored at ebs
  • A instance store-backed instance is a running machine whose image is stored at instance store
    • what is ebs
      EBS is an aws service. It stands for elastic block service.

      • Similar to s3, ebs is also a storage service. But it is only for image of ec2 instance.
      • The data in ebs is persistent even its corresponding instance is stopped.
      • The charge of ebs is additional. It is not included within instance’s hourly running cost.
      • When a instance is stopped, its corresponding ebs is still in use and charged.
      • When a instance is terminated, its instance is deleted. If the instance is ebs-backed, the ebs is also deleted at which time the ebs is stopped charged

      what is instance store
      A storage within the instance itself.

      • The physical storage of instance store is attached to the host computer.
      • The instance store could have many instance store volumes. Each instance volume could be represented as linux device, such as /dev/eupheumeral0, /dev/eupheumeral1, and so on.
      • The data in instance store is lost when its corresponding instance is stopped
      • The charge of instance store is included within instance’s hourly running cost.

      conclusion
      If persistent data is required, then choose ebs-backed instance type. But be careful that the ebs is still charged when its corresponding instance is stopped. Only when the instance is terminated does the ebs stop been charged.

      reference
      Amazon EC2 Root Device Volume
      Amazon EC2 Instance Store

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