AWS EC2 Instance Lifecycle

EC2 Instance Lifecycle Overview

  • EC2 instance lifecycle determines how an EC2 instance transitions through different states from the moment it is launched to its termination

EC2 Instance Lifecycle

Instance Launch

  •  Pending
    • When the instance is first launched is enters into the pending state
  • Running
    • After the instance is launched, it enters into the running state
    • Charges are incurred for each second, with a one-minute minimum, that the instance running is running, even if the instance remains idle

Instance Start & Stop (EBS-backed instances only)

  • Only an EBS-backed instance can be stopped and started.
  • Instance store-backed instance cannot be stopped and started.
  • An instance can be stopped & started in case the instance fails a status check or is not running as expected
  • Stop
    • After the instance is stopped, it enters in stopping state and then to stopped state.
    • Charges are only incurred for the EBS storage and not for the instance hourly charge or data transfer.
    • While the instance is stopped, its root volume can be treated like any other volume, and modified for e.g. repair file system problems or update software or change the instance type, user data, EBS optimization attributes, etc
    • Volume can be detached from the stopped instance, and attached to a running instance, modified, detached from the running instance, and then reattached to the stopped instance. It should be reattached using the storage device name that’s specified as the root device in the block device mapping for the instance.
  • Start
    • When the instance is started, it enters into pending state and then into running
    • An instance, when stopped and started, is launched on a new host
    • Any data on an instance store volume (not root volume) would be lost while data on the EBS volume persists
  • EC2 instance retains its private IP address as well as the Elastic IP address.
  • If the instance has an IPv6 address, it retains its IPv6 address.
  • However, the public IP address, if assigned instead of the Elastic IP address, would be released
  • For each transition of an instance from stopped to running, charges per second are incurred when the instance is running, with a minimum of one minute every time the instance is started

Instance Hibernate

  • Instance hibernation signals the operating system to perform hibernation (suspend-to-disk), which saves the contents from the instance memory (RAM) to the EBS root volume
  • Instance’s EBS root volume and any attached EBS data volumes are persisted, including the saved contents of the RAM.
  • Any EC2 instance store volumes remain attached to the instance, but the data on the instance store volumes is lost.
  • When the instance is restarted, the EBS root volume is restored to its previous state and the RAM contents are reloaded. Previously attached data volumes are reattached and the instance retains its instance ID.
  • After the instance is hibernated, it enters in stopping state and then to stopped state.
  • When the instance is restarted
    • It enters the pending state and the instance is moved to a new host computer (though in some cases, it remains on the current host).
    • EBS root volume is restored to its previous state
    • RAM contents are reloaded
    • Processes that were previously running on the instance are resumed
    • Previously attached data volumes are reattached and the instance retains its instance ID
    • Instance retains private IPv4 addresses and any IPv6 addresses
    • Instance retains its Elastic IP address
    • Instance releases its Public IPv4 address and would get a new one
  • Hibernation prerequisites
    • Supported instance families – C3, C4, C5, M3, M4, M5, R3, R4, R5, & T2
    • Instance RAM size – must be less than 150 GB.
    • Instance size – not supported for bare metal instances.
    • Supported AMIs must be an HVM AMI that supports hibernation
    • Root volume type – must be EBS volume and not instance store
    • EBS root volume size – must be large enough to store the RAM contents
    • EBS root volume MUST be encrypted to ensure the protection of sensitive content that is in memory at the time of hibernation
    • Enable hibernation at launch, as changing it is not supported on an existing instance
    • Purchasing options – Only On-Demand Instances and Reserved Instances supported
  • Limitations or Unsupported Actions
    • Changing the instance type or size of a hibernated instance
    • Creating snapshots or AMIs from hibernated instances or instances for which hibernation is enabled
    • the data on any instance store volumes is lost
    • can’t hibernate an instance that has more than 150 GB of RAM.
    • can’t hibernate an instance that is in an Auto Scaling group or used by ECS. If the instance is in an Auto Scaling group is hibernated, the EC2 Auto Scaling service marks the stopped instance as unhealthy, and may terminate it and launch a replacement instance.
    • An instance cannot be hibernated for more than 60 days.

Instance Reboot

  • Both EBS-backed and Instance store-backed instances can be rebooted
  • An instance remains on the same host computer and maintains its public DNS name, private IP address
  • Data on the EBS and Instance store volume is also retained
  • AWS recommends using EC2 to reboot the instance instead of running the operating system reboot command from the instance as it performs a hard reboot if the instance does not cleanly shut down within four minutes also creates an API record in CloudTrail if enabled.

Instance Retirement

  • An instance is scheduled to be retired when AWS detects an irreparable failure of the underlying hardware hosting the instance.
  • When an instance reaches its scheduled retirement date, it is stopped or terminated by AWS.
  • If the instance root device is an EBS volume, the instance is stopped and can be started again at any time.
  • If the instance root device is an instance store volume, the instance is terminated, and cannot be used again.

Instance Termination

  • An instance can be terminated, and it enters into the shutting-down, and then the terminated state
  • After an instance is terminated, it can’t be connected and no charges are incurred
  • Instance Shutdown behavior
    • Each EBS-backed instance supports the InstanceInitiatedShutdownBehavior attribute which determines whether the instance would be stopped or terminated when a shutdown command is initiated from the instance itself for e.g. shutdown, halt or poweroff command in linux
    • Default behavior for the instance to be stopped.
    • A shutdown command for an Instance store-backed instance will always terminate the instance
  • Termination protection
    • Termination protection ( DisableApiTermination attribute) can be enabled on the instance to prevent it from being accidentally terminated
    • DisableApiTermination from the Console, CLI or API.
    • Instance can be terminated through EC2 CLI.
    • Termination protection does not work for instances when
      • part of an Autoscaling group
      • launched as Spot instances
      • terminating an instance by initiating shutdown from the instance
  • Data persistence
    • EBS volume has a DeleteOnTermination  attribute which determines whether the volumes would be persisted or deleted when an instance they are associated with are terminated
    • Data on Instance store volume data does not persist
    • Default is to delete the root device volume and preserve any other EBS volumes. i.e.
      • Data on EBS root volumes have the DeleteOnTermination flag set to true and would be deleted by default
      • Additional EBS volumes attached have the DeleteOnTermination flag set to false are not deleted but just detached from the instance

EC2 Instance Lifecycle States and Billing

AWS Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • AWS services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • AWS exam questions are not updated to keep up the pace with AWS updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.
  1. What does Amazon EC2 provide?
    1. Virtual servers in the Cloud
    2. A platform to run code (Java, PHP, Python), paying on an hourly basis.
    3. Computer Clusters in the Cloud.
    4. Physical servers, remotely managed by the customer.
  2. A user has enabled termination protection on an EC2 instance. The user has also set Instance initiated shutdown behavior to terminate. When the user shuts down the instance from the OS, what will happen?
    1. The OS will shutdown but the instance will not be terminated due to protection
    2. It will terminate the instance
    3. It will not allow the user to shutdown the instance from the OS
    4. It is not possible to set the termination protection when an Instance initiated shutdown is set to Terminate
  3. A user has launched an EC2 instance and deployed a production application in it. The user wants to prohibit any mistakes from the production team to avoid accidental termination. How can the user achieve this?
    1. The user can the set DisableApiTermination attribute to avoid accidental termination
    2. It is not possible to avoid accidental termination
    3. The user can set the Deletion termination flag to avoid accidental termination
    4. The user can set the InstanceInitiatedShutdownBehavior flag to avoid accidental termination
  4. You have been doing a lot of testing of your VPC Network by deliberately failing EC2 instances to test whether instances are failing over properly. Your customer who will be paying the AWS bill for all this asks you if he being charged for all these instances. You try to explain to him how the billing works on EC2 instances to the best of your knowledge. What would be an appropriate response to give to the customer in regards to this?
    1. Billing commences when Amazon EC2 AMI instance is completely up and billing ends as soon as the instance starts to shutdown.
    2. Billing commences when Amazon EC2 initiates the boot sequence of an AMI instance and billing ends when the instance shuts down.
    3. Billing only commences only after 1 hour of uptime and billing ends when the instance terminates.
    4. Billing commences when Amazon EC2 initiates the boot sequence of an AMI instance and billing ends as soon as the instance starts to shutdown.