# Use `DescribeSubnets` with an Amazon SDK or CLI
The following code examples show how to use `DescribeSubnets`.
Action examples are code excerpts from larger programs and must be run in context. You can see this action in context in the following code examples:
+ [Build and manage a resilient service](example_cross_ResilientService_section.md)
+ [Configure Amazon ECS Service Connect](example_ecs_ServiceConnect_085_section.md)
+ [Create a basic VPC](example_vpc_GettingStartedCLI_section.md)
+ [Create an Amazon ECS Linux task for the Fargate launch type](example_ecs_GettingStarted_086_section.md)
+ [Creating an Amazon ECS service for the EC2 launch type](example_ecs_GettingStarted_018_section.md)
+ [Creating an Amazon RDS DB instance](example_rds_GettingStarted_036_section.md)
+ [Creating and managing Amazon EBS volumes](example_ec2_GettingStarted_020_section.md)
+ [Getting started with Amazon DocumentDB](example_docdb_GettingStarted_025_section.md)
+ [Getting started with Amazon MSK](example_ec2_GettingStarted_057_section.md)
+ [Getting started with Amazon VPC Transit Gateway](example_vpc_TransitGatewayGettingStarted_section.md)
+ [Getting started with Elastic Load Balancing](example_elastic_load_balancing_v2_GettingStarted_058_section.md)
------
#### [ .NET ]
**Amazon SDK for .NET**
There's more on GitHub. Find the complete example and learn how to set up and run in the [Amazon Code Examples Repository](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/dotnetv3/cross-service/ResilientService/AutoScalerActions#code-examples).
```
///
/// Get all the subnets for a Vpc in a set of availability zones.
///
/// The Id of the Vpc.
/// The list of availability zones.
/// The collection of subnet objects.
public async Task> GetAllVpcSubnetsForZones(string vpcId, List availabilityZones)
{
try
{
var subnets = new List();
var subnetPaginator = _amazonEc2.Paginators.DescribeSubnets(
new DescribeSubnetsRequest()
{
Filters = new List()
{
new("vpc-id", new List() { vpcId }),
new("availability-zone", availabilityZones),
new("default-for-az", new List() { "true" })
}
});
// Get the entire list using the paginator.
await foreach (var subnet in subnetPaginator.Subnets)
{
subnets.Add(subnet);
}
return subnets;
}
catch (AmazonEC2Exception ec2Exception)
{
if (ec2Exception.ErrorCode == "InvalidVpcID.NotFound")
{
_logger.LogError(ec2Exception, $"The specified VPC ID {vpcId} does not exist.");
}
throw;
}
catch (Exception ex)
{
_logger.LogError(ex, $"An error occurred while describing the subnets.: {ex.Message}");
throw;
}
}
```
+ For API details, see [DescribeSubnets](https://docs.amazonaws.cn/goto/DotNetSDKV3/ec2-2016-11-15/DescribeSubnets) in *Amazon SDK for .NET API Reference*.
------
#### [ CLI ]
**Amazon CLI**
**Example 1: To describe all your subnets**
The following `describe-subnets` example displays the details of your subnets.
```
aws ec2 describe-subnets
```
Output:
```
{
"Subnets": [
{
"AvailabilityZone": "us-east-1d",
"AvailabilityZoneId": "use1-az2",
"AvailableIpAddressCount": 4089,
"CidrBlock": "172.31.80.0/20",
"DefaultForAz": true,
"MapPublicIpOnLaunch": false,
"MapCustomerOwnedIpOnLaunch": true,
"State": "available",
"SubnetId": "subnet-0bb1c79de3EXAMPLE",
"VpcId": "vpc-0ee975135dEXAMPLE",
"OwnerId": "111122223333",
"AssignIpv6AddressOnCreation": false,
"Ipv6CidrBlockAssociationSet": [],
"CustomerOwnedIpv4Pool:": 'pool-2EXAMPLE',
"SubnetArn": "arn:aws:ec2:us-east-2:111122223333:subnet/subnet-0bb1c79de3EXAMPLE",
"EnableDns64": false,
"Ipv6Native": false,
"PrivateDnsNameOptionsOnLaunch": {
"HostnameType": "ip-name",
"EnableResourceNameDnsARecord": false,
"EnableResourceNameDnsAAAARecord": false
}
},
{
"AvailabilityZone": "us-east-1d",
"AvailabilityZoneId": "use1-az2",
"AvailableIpAddressCount": 4089,
"CidrBlock": "172.31.80.0/20",
"DefaultForAz": true,
"MapPublicIpOnLaunch": true,
"MapCustomerOwnedIpOnLaunch": false,
"State": "available",
"SubnetId": "subnet-8EXAMPLE",
"VpcId": "vpc-3EXAMPLE",
"OwnerId": "1111222233333",
"AssignIpv6AddressOnCreation": false,
"Ipv6CidrBlockAssociationSet": [],
"Tags": [
{
"Key": "Name",
"Value": "MySubnet"
}
],
"SubnetArn": "arn:aws:ec2:us-east-1:111122223333:subnet/subnet-8EXAMPLE",
"EnableDns64": false,
"Ipv6Native": false,
"PrivateDnsNameOptionsOnLaunch": {
"HostnameType": "ip-name",
"EnableResourceNameDnsARecord": false,
"EnableResourceNameDnsAAAARecord": false
}
}
]
}
```
For more information, see [Working with VPCs and Subnets](https://docs.aws.amazon.com/vpc/latest/userguide/working-with-vpcs.html) in the *Amazon VPC User Guide*.
**Example 2: To describe the subnets of a specific VPC**
The following `describe-subnets` example uses a filter to retrieve details for the subnets of the specified VPC.
```
aws ec2 describe-subnets \
--filters "Name=vpc-id,Values=vpc-3EXAMPLE"
```
Output:
```
{
"Subnets": [
{
"AvailabilityZone": "us-east-1d",
"AvailabilityZoneId": "use1-az2",
"AvailableIpAddressCount": 4089,
"CidrBlock": "172.31.80.0/20",
"DefaultForAz": true,
"MapPublicIpOnLaunch": true,
"MapCustomerOwnedIpOnLaunch": false,
"State": "available",
"SubnetId": "subnet-8EXAMPLE",
"VpcId": "vpc-3EXAMPLE",
"OwnerId": "1111222233333",
"AssignIpv6AddressOnCreation": false,
"Ipv6CidrBlockAssociationSet": [],
"Tags": [
{
"Key": "Name",
"Value": "MySubnet"
}
],
"SubnetArn": "arn:aws:ec2:us-east-1:111122223333:subnet/subnet-8EXAMPLE",
"EnableDns64": false,
"Ipv6Native": false,
"PrivateDnsNameOptionsOnLaunch": {
"HostnameType": "ip-name",
"EnableResourceNameDnsARecord": false,
"EnableResourceNameDnsAAAARecord": false
}
}
]
}
```
For more information, see [Working with VPCs and Subnets](https://docs.aws.amazon.com/vpc/latest/userguide/working-with-vpcs.html) in the *Amazon VPC User Guide*.
**Example 3: To describe the subnets with a specific tag**
The following `describe-subnets` example uses a filter to retrieve the details of those subnets with the tag `CostCenter=123` and the `--query` parameter to display the subnet IDs of the subnets with this tag.
```
aws ec2 describe-subnets \
--filters "Name=tag:CostCenter,Values=123" \
--query "Subnets[*].SubnetId" \
--output text
```
Output:
```
subnet-0987a87c8b37348ef
subnet-02a95061c45f372ee
subnet-03f720e7de2788d73
```
For more information, see [Working with VPCs and Subnets](https://docs.aws.amazon.com/vpc/latest/userguide/working-with-vpcs.html) in the *Amazon VPC User Guide*.
+ For API details, see [DescribeSubnets](https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ec2/describe-subnets.html) in *Amazon CLI Command Reference*.
------
#### [ JavaScript ]
**SDK for JavaScript (v3)**
There's more on GitHub. Find the complete example and learn how to set up and run in the [Amazon Code Examples Repository](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javascriptv3/example_code/cross-services/wkflw-resilient-service#code-examples).
```
const client = new EC2Client({});
const { Subnets } = await client.send(
new DescribeSubnetsCommand({
Filters: [
{ Name: "vpc-id", Values: [state.defaultVpc] },
{ Name: "availability-zone", Values: state.availabilityZoneNames },
{ Name: "default-for-az", Values: ["true"] },
],
}),
);
```
+ For API details, see [DescribeSubnets](https://docs.amazonaws.cn/AWSJavaScriptSDK/v3/latest/client/ec2/command/DescribeSubnetsCommand) in *Amazon SDK for JavaScript API Reference*.
------
#### [ PowerShell ]
**Tools for PowerShell V4**
**Example 1: This example describes the specified subnet.**
```
Get-EC2Subnet -SubnetId subnet-1a2b3c4d
```
**Output:**
```
AvailabilityZone : us-west-2c
AvailableIpAddressCount : 251
CidrBlock : 10.0.0.0/24
DefaultForAz : False
MapPublicIpOnLaunch : False
State : available
SubnetId : subnet-1a2b3c4d
Tags : {}
VpcId : vpc-12345678
```
**Example 2: This example describes all your subnets.**
```
Get-EC2Subnet
```
+ For API details, see [DescribeSubnets](https://docs.aws.amazon.com/powershell/v4/reference) in *Amazon Tools for PowerShell Cmdlet Reference (V4)*.
**Tools for PowerShell V5**
**Example 1: This example describes the specified subnet.**
```
Get-EC2Subnet -SubnetId subnet-1a2b3c4d
```
**Output:**
```
AvailabilityZone : us-west-2c
AvailableIpAddressCount : 251
CidrBlock : 10.0.0.0/24
DefaultForAz : False
MapPublicIpOnLaunch : False
State : available
SubnetId : subnet-1a2b3c4d
Tags : {}
VpcId : vpc-12345678
```
**Example 2: This example describes all your subnets.**
```
Get-EC2Subnet
```
+ For API details, see [DescribeSubnets](https://docs.aws.amazon.com/powershell/v5/reference) in *Amazon Tools for PowerShell Cmdlet Reference (V5)*.
------
#### [ Python ]
**SDK for Python (Boto3)**
There's more on GitHub. Find the complete example and learn how to set up and run in the [Amazon Code Examples Repository](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/python/example_code/ec2#code-examples).
```
class AutoScalingWrapper:
"""
Encapsulates Amazon EC2 Auto Scaling and EC2 management actions.
"""
def __init__(
self,
resource_prefix: str,
inst_type: str,
ami_param: str,
autoscaling_client: boto3.client,
ec2_client: boto3.client,
ssm_client: boto3.client,
iam_client: boto3.client,
):
"""
Initializes the AutoScaler class with the necessary parameters.
:param resource_prefix: The prefix for naming AWS resources that are created by this class.
:param inst_type: The type of EC2 instance to create, such as t3.micro.
:param ami_param: The Systems Manager parameter used to look up the AMI that is created.
:param autoscaling_client: A Boto3 EC2 Auto Scaling client.
:param ec2_client: A Boto3 EC2 client.
:param ssm_client: A Boto3 Systems Manager client.
:param iam_client: A Boto3 IAM client.
"""
self.inst_type = inst_type
self.ami_param = ami_param
self.autoscaling_client = autoscaling_client
self.ec2_client = ec2_client
self.ssm_client = ssm_client
self.iam_client = iam_client
sts_client = boto3.client("sts")
self.account_id = sts_client.get_caller_identity()["Account"]
self.key_pair_name = f"{resource_prefix}-key-pair"
self.launch_template_name = f"{resource_prefix}-template-"
self.group_name = f"{resource_prefix}-group"
# Happy path
self.instance_policy_name = f"{resource_prefix}-pol"
self.instance_role_name = f"{resource_prefix}-role"
self.instance_profile_name = f"{resource_prefix}-prof"
# Failure mode
self.bad_creds_policy_name = f"{resource_prefix}-bc-pol"
self.bad_creds_role_name = f"{resource_prefix}-bc-role"
self.bad_creds_profile_name = f"{resource_prefix}-bc-prof"
def get_subnets(self, vpc_id: str, zones: List[str] = None) -> List[Dict[str, Any]]:
"""
Gets the default subnets in a VPC for a specified list of Availability Zones.
:param vpc_id: The ID of the VPC to look up.
:param zones: The list of Availability Zones to look up.
:return: The list of subnets found.
"""
# Ensure that 'zones' is a list, even if None is passed
if zones is None:
zones = []
try:
paginator = self.ec2_client.get_paginator("describe_subnets")
page_iterator = paginator.paginate(
Filters=[
{"Name": "vpc-id", "Values": [vpc_id]},
{"Name": "availability-zone", "Values": zones},
{"Name": "default-for-az", "Values": ["true"]},
]
)
subnets = []
for page in page_iterator:
subnets.extend(page["Subnets"])
log.info("Found %s subnets for the specified zones.", len(subnets))
return subnets
except ClientError as err:
log.error(
f"Failed to retrieve subnets for VPC '{vpc_id}' in zones {zones}."
)
error_code = err.response["Error"]["Code"]
if error_code == "InvalidVpcID.NotFound":
log.error(
"The specified VPC ID does not exist. "
"Please check the VPC ID and try again."
)
# Add more error-specific handling as needed
log.error(f"Full error:\n\t{err}")
```
+ For API details, see [DescribeSubnets](https://docs.amazonaws.cn/goto/boto3/ec2-2016-11-15/DescribeSubnets) in *Amazon SDK for Python (Boto3) API Reference*.
------
For a complete list of Amazon SDK developer guides and code examples, see [Create Amazon EC2 resources using an Amazon SDK](sdk-general-information-section.md). This topic also includes information about getting started and details about previous SDK versions.