Question

试图了解describe_instances（）的工作方式这是一个代码，为我提供了我目前拥有的所有实例的实例ID，因此我得到了3个实例ID

    import boto3 
    from pprint import pprint

    ec2=boto3.client('ec2') 
    response=ec2.describe_instances()
    instancelist = [] 
   for reservation in (response["Reservations"]):
        for instance in reservation["Instances"]:
            instancelist.append(instance["InstanceId"]) print (instancelist)

提供我输出

['i-03e7f6391a0f523ee'，'i-0e12c8dad5fb6d8c5'，'i-002adcd0913e4d673']

但是如果我写以下内容

import boto3
from pprint import pprint
ec2=boto3.client('ec2')
response=ec2.describe_instances()
for x in response:
    print (x)
    print ("in for loop")

我只得到以下输出

Reservations
in for loop
ResponseMetadata
in for loop

我期望的是实例的实例ID。现在我写了以下

import boto3
from pprint import pprint

ec2=boto3.client('ec2')
response=ec2.describe_instances()

print (response["Reservations"][0]["Instances"][0]["InstanceId"])
print (response["Reservations"][1]["Instances"][0]["InstanceId"])
print (response["Reservations"][1]["Instances"][1]["InstanceId"])

我得到输出

i-03e7f6391a0f523ee i-0e12c8dad5fb6d8c5 i-002adcd0913e4d673

如果按以下方式编写，则上述打印声明无效

print (response["Reservations"][2]["Instances"][0]["InstanceId"])

出现错误

    print (response["Reservations"][2]["Instances"][1]["InstanceId"])
IndexError: list index out of range

我无法理解的是语句中describe_instances方法如何返回值

response=ec2.describe_instances()

为什么上面我使用x的for循环没有给出输出。我在这里阅读了文档 https://boto3.readthedocs.io/en/latest/reference/services/ec2.html#EC2.Client.describe_instances 据我了解ec2.describe_instances（）返回一个dictionary（）包含DescribeInstances的输出。 •预订（清单）- 零个或多个预订。因此，基于这种理解，我认为我应该能够通过

遍历列表成员

response["Reservations"][0]
response["Reservations"][1]
response["Reservations"][2]

但这给了我错误

print(response["Reservations"][2])
IndexError: list index out of range

我无法理解通过ec2.describe_instances（）收到的响应

按照以下答案的要求输出打印（响应）

    {'Reservations': [

    {'Groups': [], 'Instances': [{'AmiLaunchIndex': 0, 'ImageId': 'ami-d783a9b8', 

    'InstanceId': 'i-03e7f6391a0f523ee', 'InstanceType': 't2.micro', 'KeyName': 'datastructutre key', 

    'LaunchTime': datetime.datetime(2018, 8, 25, 10, 3, 53, tzinfo=tzutc()), 'Monitoring': {'State': 

    'disabled'}, 'Placement': {'AvailabilityZone': 'ap-south-1a', 'GroupName': '', 'Tenancy': 

    'default'}, 'PrivateDnsName': 'ip-172-31-20-16.ap-south-1.compute.internal', 'PrivateIpAddress': 

    '172.31.20.16', 'ProductCodes': [], 'PublicDnsName': '', 'State': {'Code': 80, 'Name': 

    'stopped'}, 'StateTransitionReason': 'User initiated (2018-08-25 10:07:17 GMT)', 'SubnetId': 

    'subnet-d3fdbabb', 'VpcId': 'vpc-08356c60', 'Architecture': 'x86_64', 'BlockDeviceMappings': 

    [{'DeviceName': '/dev/xvda', 'Ebs': {'AttachTime': datetime.datetime(2018, 8, 1, 4, 28, 52, 

    tzinfo=tzutc()), 'DeleteOnTermination': True, 'Status': 'attached', 'VolumeId': 'vol-

    09716d3308f44c63f'}}], 'ClientToken': '', 'EbsOptimized': False, 'EnaSupport': True, 

    'Hypervisor': 'xen', 'NetworkInterfaces': [{'Attachment': {'AttachTime': datetime.datetime(2018, 

    8, 1, 4, 28, 52, tzinfo=tzutc()), 'AttachmentId': 'eni-attach-08d060230b617ca70', 

    'DeleteOnTermination': True, 'DeviceIndex': 0, 'Status': 'attached'}, 'Description': '', 

    'Groups': [{'GroupName': 'launch-wizard-1', 'GroupId': 'sg-0e81c2a33e1039f58'}, {'GroupName': 

    'default', 'GroupId': 'sg-40e5492a'}], 'Ipv6Addresses': [], 'MacAddress': '02:5a:17:52:69:a6', 

    'NetworkInterfaceId': 'eni-0146aab6d9503bf47', 'OwnerId': '11000101010', 'PrivateDnsName': 'ip-

    172-31-20-16.ap-south-1.compute.internal', 'PrivateIpAddress': '172.31.20.16', 

    'PrivateIpAddresses': [{'Primary': True, 'PrivateDnsName': 'ip-172-31-20-16.ap-south-

    1.compute.internal', 'PrivateIpAddress': '172.31.20.16'}], 'SourceDestCheck': True, 'Status': 

    'in-use', 'SubnetId': 'subnet-d3fdbabb', 'VpcId': 'vpc-08356c60'}], 'RootDeviceName': 

    '/dev/xvda', 'RootDeviceType': 'ebs', 'SecurityGroups': [{'GroupName': 'launch-wizard-1', 

    'GroupId': 'sg-0e81c2a33e1039f58'}, {'GroupName': 'default', 'GroupId': 'sg-40e5492a'}], 

    'SourceDestCheck': True, 'StateReason': {'Code': 'Client.UserInitiatedShutdown', 'Message': 

    'Client.UserInitiatedShutdown: User initiated shutdown'}, 'VirtualizationType': 'hvm', 

    'CpuOptions': {'CoreCount': 1, 'ThreadsPerCore': 1}}], 'OwnerId': '11000101010', 'ReservationId': 

    'r-0571937a9ea83fac4'}, 

  {'Groups': [], 'Instances': [

{'AmiLaunchIndex': 0, 'ImageId': 'ami-00b6a8a2bd28daf19', 'InstanceId': 'i-0e12c8dad5fb6d8c5', 'InstanceType': 't2.micro', 'KeyName': 'datastructutre key', 'LaunchTime': datetime.datetime(2018, 8, 25, 10, 3, 53, tzinfo=tzutc()), 'Monitoring': {'State': 'disabled'}, 'Placement': {'AvailabilityZone': 'ap-south-1a', 'GroupName': '', 'Tenancy': 'default'}, 'PrivateDnsName': 'ip-172-31-28-39.ap-south-1.compute.internal', 'PrivateIpAddress': '172.31.28.39', 'ProductCodes': [], 'PublicDnsName': '', 'State': {'Code': 80, 'Name': 'stopped'}, 'StateTransitionReason': 'User initiated (2018-08-25 10:07:17 GMT)', 'SubnetId': 'subnet-d3fdbabb', 'VpcId': 'vpc-08356c60', 'Architecture': 'x86_64', 'BlockDeviceMappings': [{'DeviceName': '/dev/xvda', 'Ebs': {'AttachTime': datetime.datetime(2018, 8, 22, 21, 33, 44, tzinfo=tzutc()), 'DeleteOnTermination': True, 'Status': 'attached', 'VolumeId': 'vol-01d5ce67c9f1b081e'}}], 'ClientToken': '', 'EbsOptimized': False, 'EnaSupport': True, 'Hypervisor': 'xen', 'NetworkInterfaces': [{'Attachment': {'AttachTime': datetime.datetime(2018, 8, 22, 21, 33, 44, tzinfo=tzutc()), 'AttachmentId': 'eni-attach-0cbdea888315049ae',  'DeleteOnTermination': True, 'DeviceIndex': 0, 'Status': 'attached'}, 'Description': '',  'Groups': [{'GroupName': 'default', 'GroupId': 'sg-40e5492a'}], 'Ipv6Addresses': [], 'MacAddress': '02:f4:b8:bd:84:26', 'NetworkInterfaceId': 'eni-0d99a7669a1e4b9db', 'OwnerId': '11000101010', 'PrivateDnsName': 'ip-172-31-28-39.ap-south-1.compute.internal', 'PrivateIpAddress': '172.31.28.39', 'PrivateIpAddresses': [{'Primary': True, 'PrivateDnsName': 'ip-172-31-28-39.ap-south-1.compute.internal', 'PrivateIpAddress': '172.31.28.39'}], 'SourceDestCheck': True, 'Status': 'in-use', 'SubnetId': 'subnet-d3fdbabb', 'VpcId': 'vpc-08356c60'}], 'RootDeviceName': '/dev/xvda', 'RootDeviceType': 'ebs', 'SecurityGroups': [{'GroupName': 'default', 'GroupId': 'sg-40e5492a'}], 'SourceDestCheck': True, 'StateReason': {'Code': 'Client.UserInitiatedShutdown', 'Message': 'Client.UserInitiatedShutdown: User initiated shutdown'}, 'VirtualizationType': 'hvm', 'CpuOptions': {'CoreCount': 1, 'ThreadsPerCore': 1}}, 

{'AmiLaunchIndex': 1, 'ImageId': 'ami-00b6a8a2bd28daf19', 'InstanceId': 'i-002adcd0913e4d673', 'InstanceType': 't2.micro', 'KeyName': 'datastructutre key', 'LaunchTime': datetime.datetime (2018, 8, 25, 10, 3, 53, tzinfo=tzutc()), 'Monitoring': {'State': 'disabled'}, 'Placement': {'AvailabilityZone': 'ap-south-1a', 'GroupName': '', 'Tenancy': 'default'}, 'PrivateDnsName': 'ip-172-31-30-108.ap-south-1.compute.internal', 'PrivateIpAddress': '172.31.30.108', 'ProductCodes': [], 'PublicDnsName': '', 'State': {'Code': 80, 'Name': 'stopped'}, 'StateTransitionReason': 'User initiated (2018-08-25 10:07:17 GMT)', 'SubnetId': 'subnet-d3fdbabb', 'VpcId': 'vpc-08356c60', 'Architecture': 'x86_64', 'BlockDeviceMappings': [{'DeviceName': '/dev/xvda', 'Ebs': {'AttachTime': datetime.datetime(2018, 8, 22, 21, 33, 44, tzinfo=tzutc()), 'DeleteOnTermination': True, 'Status': 'attached', 'VolumeId': 'vol-0f0c49cc912a083f3'}}], 'ClientToken': '', 'EbsOptimized': False, 'EnaSupport': True, 'Hypervisor': 'xen', 'NetworkInterfaces': [{'Attachment': {'AttachTime': datetime.datetime(2018, 8, 22, 21, 33, 44, tzinfo=tzutc()), 'AttachmentId': 'eni-attach-0f35d1842b76cff9a', 'DeleteOnTermination': True, 'DeviceIndex': 0, 'Status': 'attached'}, 'Description': '', 'Groups': [{'GroupName': 'default', 'GroupId': 'sg-40e5492a'}], 'Ipv6Addresses': [], 'MacAddress': '02:21:d4:20:22:c6', 'NetworkInterfaceId': 'eni-0e3797492dc4e3299', 'OwnerId': '11000101010', 'PrivateDnsName': 'ip-172-31-30-108.ap-south-1.compute.internal', 'PrivateIpAddress': '172.31.30.108', 'PrivateIpAddresses': [{'Primary': True, 'PrivateDnsName': 'ip-172-31-30-108.ap-south-1.compute.internal', 'PrivateIpAddress': '172.31.30.108'}], 'SourceDestCheck': True, 'Status': 'in-use', 'SubnetId': 'subnet-d3fdbabb', 'VpcId': 'vpc-08356c60'}], 'RootDeviceName': '/dev/xvda', 'RootDeviceType': 'ebs', 'SecurityGroups': [{'GroupName': 'default', 'GroupId': 'sg-40e5492a'}], 'SourceDestCheck': True, 'StateReason': {'Code': 'Client.UserInitiatedShutdown', 'Message': 'Client.UserInitiatedShutdown: User initiated shutdown'}, 'VirtualizationType': 'hvm', 'CpuOptions': {'CoreCount': 1, 'ThreadsPerCore': 1}}], 'OwnerId': 'ReservationId': 'r-05cff59b2524ed79c'}], 

'ResponseMetadata': {'RequestId': 'fc80ae94-dd46-4c71-93f5-a38d6ede800c', 'HTTPStatusCode': 200, 'HTTPHeaders': {'content-type':'text/xml;charset=UTF-8', 'transfer-encoding': 'chunked', 'vary': 'Accept-Encoding', 'date': 'Sat, 25 Aug 2018 17:13:51 GMT', 'server': 'AmazonEC2'}, 'RetryAttempts': 0}}

您可以在上面的输出中注意到{'Groups': [], 'Instances': [{'AmiLaunchIndex': 0,第2行，而注意到'AmiLaunchIndex': 1, 'ImageId': 'ami-00b6a8a2bd28daf19'两次，而第一个实例是'AmiLaunchIndex': 0, 'ImageId': 'ami-d783a9b8',，我是通过run_instance method（）创建这些实例的正如您在打印（响应）输出中看到的那样，只是输出来了，但这并不能给出清晰的图片，或者我无法理解这其中的三个实例在哪里？

Answer 1

您会看到以下错误：

print(response["Reservations"][2])
IndexError: list index out of range

它表明您正在尝试获取元素Reservations的第二个实例，但给定的返回中不存在该实例。我想请您通过使用response=ec2.describe_instances()在终端上将其打印出来以熟悉该函数的data_type / return来检查函数print(response)的返回。这将帮助您更好地了解下次调用此函数的期望。

此外，当您知道将要获得的回报类型时，以后使用for loop之类的元素来对元素（您的函数， response=ec2.describe_instances()根据其文档返回。），然后将response用于您要实现的目标。

希望有帮助。快乐编码：）

Answer 2

基本上，响应对象将返回一个或多个Reservation对象。

response=ec2.describe_instances()

除了出于迭代目的，您实际上不必担心保留。要深入研究，您可以查看过去的问题，

https://serverfault.com/questions/749118/aws-ec2-what-is-a-reservation-id-exactly-and-what-does-it-represent

因此，您的第一段代码是列出所有EC2实例的实例ID的合适方法。

第二段代码遍历响应对象（即字典）中的键

response=ec2.describe_instances()
for x in response:
    print(x)

这是EC2服务的Boto文档，您可以在其中找到有关响应对象的更多信息，

https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/ec2.html#EC2.Client.describe_instances

Answer 3

您还可以使用列表推导来获取此数据。示例：

  #!/usr/bin/env python3
  import boto3

  # Creating the boto client
  client = boto3.client('ec2')

  # Get the instance list
  instance_details = client.describe_instances(
    InstanceIds=[
      instance_id,
    ],
  )
  # Get all the Instance details from the Reservations
  # wrapping instances in [] prevents creating a outer list
  [instances] = [x['Instances']for x in i_details['Reservations']]

试图了解describe_instances（）的工作方式

3 个答案: