Accessing help and resources for the AWS CLI

The name of the command.

NAME
       describe-instances -

A description of the API operation that the command invokes.

DESCRIPTION
       Describes one or more of your instances.

       If you specify one or more instance IDs, Amazon EC2 returns information
       for those instances. If you do not specify  instance  IDs,  Amazon  EC2
       returns  information  for  all  relevant  instances.  If you specify an
       instance ID that is not valid, an error is returned. If you specify  an
       instance  that  you  do  not  own,  it  is not included in the returned
       results.
...

The basic syntax for using the command and its options. If an option is shown in square brackets, it's optional, has a default value, or has an alternative option that you can use.

SYNOPSIS
            describe-instances
          [--dry-run | --no-dry-run]
          [--instance-ids <value>]
          [--filters <value>]
          [--cli-input-json <value>]
          [--starting-token <value>]
          [--page-size <value>]
          [--max-items <value>]
          [--generate-cli-skeleton]

For example, describe-instances has a default behavior that describes all instances in the current account and AWS Region. You can optionally specify a list of instance-ids to describe one or more instances; dry-run is an optional Boolean flag that doesn't take a value. To use a Boolean flag, specify either shown value, in this case --dry-run or --no-dry-run. Likewise, --generate-cli-skeleton doesn't take a value. If there are conditions on an option's use, they are described in the OPTIONS section, or shown in the examples.

A description of each of the options shown in the synopsis.

OPTIONS
       --dry-run | --no-dry-run (boolean)
          Checks whether you have the required  permissions  for  the  action,
          without actually making the request, and provides an error response.
          If you have the required permissions, the error response is  DryRun-
          Operation . Otherwise, it is UnauthorizedOperation .

       --instance-ids (list)
          One or more instance IDs.

          Default: Describes all your instances.
...

Examples showing the usage of the command and its options. If no example is available for a command or use case that you need, request one using the feedback link on this page, or in the AWS CLI command reference on the help page for the command.

    EXAMPLES
    To describe an Amazon EC2 instance

    Command:
    
    aws ec2 describe-instances --instance-ids i-5203422c
    
    To describe all instances with the instance type m1.small
    
    Command:
    
    aws ec2 describe-instances --filters "Name=instance-type,Values=m1.small"
    
    To describe all instances with an Owner tag
    
    Command:
    
    aws ec2 describe-instances --filters "Name=tag-key,Values=Owner"
...

Descriptions of each of the fields and data types included in the response from AWS.

For describe-instances, the output is a list of reservation objects, each of which contains several fields and objects that contain information about the instances associated with it. This information comes from the API documentation for the reservation data type used by Amazon EC2.

OUTPUT
       Reservations -> (list)
          One or more reservations.

          (structure)
              Describes a reservation.

              ReservationId -> (string)
                 The ID of the reservation.

              OwnerId -> (string)
                 The ID of the AWS account that owns the reservation.

              RequesterId -> (string)
                 The ID of the requester that launched the instances  on  your
                 behalf (for example, AWS Management Console or Auto Scaling).

              Groups -> (list)
                 One or more security groups.

                 (structure)
                     Describes a security group.

                     GroupName -> (string)
                        The name of the security group.

                     GroupId -> (string)
                        The ID of the security group.

              Instances -> (list)
                 One or more instances.

                 (structure)
                     Describes an instance.

                     InstanceId -> (string)
                        The ID of the instance.

                     ImageId -> (string)
                        The ID of the AMI used to launch the instance.

                     State -> (structure)
                        The current state of the instance.

                        Code -> (integer)
                            The  low  byte represents the state. The high byte
                            is an opaque internal value and should be ignored.
...

When the AWS CLI renders the output into JSON, it becomes an array of reservation objects, similar to the following example.

{
    "Reservations": [
        {
            "OwnerId": "012345678901",
            "ReservationId": "r-4c58f8a0",
            "Groups": [],
            "RequesterId": "012345678901",
            "Instances": [
                {
                    "Monitoring": {
                        "State": "disabled"
                    },
                    "PublicDnsName": "ec2-52-74-16-12.us-west-2.compute.amazonaws.com",
                    "State": {
                        "Code": 16,
                        "Name": "running"
                    },
...

Each reservation object contains fields describing the reservation and an array of instance objects, each with its own fields (for example, PublicDnsName) and objects (for example, State) that describe it.

C:\> aws ec2 describe-instances help | more