There are some servers that are in private subnet and some are in public subnet.
I want to remove nat gateway and make all instances that were in private subnet to get access through internet gateway. Please suggest me the procedure.
When I have added internet gateway and removed Natgateway then started getting API timeout, please suggest me the possible reason for the same.
A "Public Subnet" is defined as a subnet that has a Route Table entry that points to an Internet Gateway.
Thus, if you want instances in the private subnet to have direct access to the Internet via the Internet Gateway, you will need to convert the private subnet into a public subnet. This can be done by adding a Route to the subnet's Route Table that directs traffic with a destination of 0.0.0.0/0 to the Internet Gateway.
Resources in the VPC that need to communicate with the Internet will need to be assigned Public IP addresses. This can be done for existing resources by assigning an Elastic IP address (which is a static IP address). However, there is a limit on the number of Elastic IP addresses available in each region.
Any new Amazon EC2 instances launched can be given a public IP address during launch, so they won't need an Elastic IP address.
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I need to migrate a big cluster of VMs to AWS. Some of these have Public IPs, others only local IPs. Is it possible to create mixed subnetwork of Public and Private IPs within a VPC such that instances with a Public IP access the Internet via an Elastic IP and the Internet Gateway and such that instances that don't have a Public IP go to the Internet over NAT. The local IP instances must be in a single subnetwork such as 192.168.1.0/24.
Is it possible how to do this? and what would be an optimal approach?
By definition, a public subnet has a route to an Internet Gateway. Anything in that subnet that needs to access the Internet will need a public IP (not necessarily an Elastic IP, just a public IP) assigned to it.
If a subnet's traffic is routed to an internet gateway, the subnet is known as a public subnet.
Similarly, by definition a private subnet is a subnet without an Internet Gateway, which relies on route to a NAT Gateway to access the Internet.
If a subnet doesn't have a route to the internet gateway, the subnet
is known as a private subnet.
Per your question, no, there's no way to have a single route table that routes traffic to both an Internet Gateway and a NAT Gateway based on the presence or lack of a public IP address on the source server.
As described in the aws VPC scenario 2 page I have a VPC with 2 subnets defined - one private and one public. The private subnet uses a NAT gateway for the outbound traffic (the NAT gateway lives in the public subnet). The public subnet uses an internet gateway for inbound and outbound.
The usage of the NAT gateway requires an ElasticIP to be registered and associated with that NAT. Now, I need a public IP for the EC2 instance I have in the public subnet, that remains static even after restarting the instance, where outside traffic can come into. Do I need to register another ElasticIP for that purpose, or can I reuse the same ElasticIP that I already created for the NAT Gateway?
An Elastic IP address can only be registered to one ENI at a single time. When you create it a mapping is formed to resolve the elastic IP address to a single private address on an ENI (be that a NAT Gateway or an EC2 host).
When you associate an Elastic IP address with an instance, it is also associated with the instance's primary network interface. When you associate an Elastic IP address with a network interface that is attached to an instance, it is also associated with the instance.
You will need to create a new one for your EC2 host, by default you can use 5 elastic IP addresses in a region, if you need more than this you would need to contact Amazon to increase your accounts quota.
For more information take a look at the Elastic IP addresses page.
One of my instances in a private subnet in a VPC in AWS , is making requests to a API (to fetch some metadata). The API provider is asking for an IP address to whitelist.
I'm not sure which IP address should I be providing since the instance is a part of an auto scaling group. It does have an ENI IP , however I'm not sure if that's the IP which they would need to whitelist. Could it be the NAT gateway IP (since the instances use a NAT gateway to connect to the internet) ?
So you have an instance in private subnet and also in auto scaling group. which needs to be whitelisted. What you can do is that you attach a NAT Gateway to the private subnet. This NAT gateway will have an public elastic IP which you can whitelist from API side.
Private Subnet are not meant to be having a public IP address, assigning public address would nullify the benefit that you would like to get from Private subnet.
However, Many users above about suggested correct option. By having a NAT gateway ( with elastic IP address ) and then configuring the private routing table with NAT gateway would allow the internet traffic ( from allowed IP address configured in private routing table) . Since all outgoing traffic would be going through the NAT gateway you can use the elastic IP address attached with NAT gateway to get whitelisted the API Provider.
You mean to say, your VPC have private subnet and public subnet. Your EC2 instances are in private subnet and you want to whitelist IP address of those EC2 instances. You can't have public IP addresses of EC2 in private instance. If you have private and public subnet architecture then you should set up ELB into public subnet and attach it to auto scaling group of EC2 instances into private subnet.
Check link about auto scaling group.
The NAT gateway has different purpose, you can't share NAT ip for whitelisting. Refer link to see, how Auto Scaling group created and how ELB attached to it.
You should share ELB IP address to provider for whitelisting.
An Internet gateway serves two purposes: to provide a target in your VPC route tables for Internet-routable traffic, and to perform network address translation (NAT) for instances that have been assigned public IPv4 addresses.
Source: https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Internet_Gateway.html
If the instances mentioned above have public IPv4 addresses, why does the Internet Gateway need to perform Network Address Translation? It would be great to have an example of a network flow that would be broken for a scenario with
VPC subnet with Internet Gateway attached
instances in that VPC subnet with IP addresses (Elastic IPs in AWS VPC parlance) in the public IP address space
hosts on the Internet unable to send packets to these instances without the Internet Gateway performing NAT
Despite of EC2 ( or to be specific: ENI associated with that EC2) instance having associated with public IP address. It is not aware about it!
This is from the same URL which was shared in original link.
" Your instance is only aware of the private (internal) IP address space defined within the VPC and subnet"
This means all network traffic which is going out/coming in to ENI is via private IP address.
If you look at the diagram on the same page, you will see a router.
This router
Does routing within VPC across all its subnets
Does routing to Internet gateway
EC2/ENI will interact with this router.
After router directs traffic to Internet Gateway (IGW):
IGW have mapping of (public ip - private ip ) of EC2 instances within that VPC.
Steps of EC2 sending traffic to Internet
EC2 with private 10.0.1.1 IP sends request to google.com (curl google.com) or tried to access public aws construct like s3
Let's assume that this is public subnet. So Router associated with this subnet will forward this traffic to default route (0.0.0.0/0) to IGW
IGW looks up its internal table (private ip: public ip). Does NAT translation using that table.
I would have liked to describe your scenario but I did not understand why IGW will not perform NAT.
The instance side of an ENI only has a private address. Public addresses are done by associating an Elastic IP or assigning a public address. Mapping of these public addresses comes from the NAT functionality of the Internet Gateway.
Your instance is only aware of the private (internal) IP address space defined within the VPC and subnet. The Internet gateway logically provides the one-to-one NAT on behalf of your instance, so that when traffic leaves your VPC subnet and goes to the Internet, the reply address field is set to the public IPv4 address or Elastic IP address of your instance, and not its private IP address. Conversely, traffic that's destined for the public IPv4 address or Elastic IP address of your instance has its destination address translated into the instance's private IPv4 address before the traffic is delivered to the VPC.
Quote from the same documentation linked in the question.
The flow for inbound traffic is Public Address -> Internet Gateway -> Private Address.
If the hosts are in a subnet without a route table that has a default route defined through the IGW, then the instance will not be able to return traffic.
I working on aws. I created a public subnet which has a network ACL allows all net traffic, and associated with a internet gateway in the route table.
And then I create a ec2 instance without elastic ip and a ec2 instance with elastic ip in it, and the security group also allows all traffic.
I ssh to the instance which has elastic ip. It works well when I run yum update and curl www.baidu.com and so on. But I can't access internet when I ssh to the ec2 instance which has no elastic ip. anyone knows that is why?
For accessing internet from EC2 instance in public subnet using Internet Gateway, the instance needs to have public IP address. Either one can configure the instance to have public IP address or attach EIP.
Reference: http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Internet_Gateway.html
If you do not want to attach public IP address for instances with Internet access (consider private subnets), NAT instance and NAT gateway can help.
Reference: http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-nat.html
As well as being in a subnet that has a route to an Internet gateway, an instance must have a public IP address to communicate with the outside world (this is distinct from an elastic IP).
You can specify this when launching an instance, if not there is a per subnet setting that controls this. The per subnet setting defaults to false other than default subnets in your default VPC. There are more details in the aws docs.
The problem lies with the gateway connected to the subnet you are using. To check the gateway you are using:
Go to the subnet you are using
Click on the Route table
Under Routes -> Destination look for 0.0.0.0/0 and check the gateway you have for it under Target
Here's how the gateways behave:
Internet Gateway (IGW) allows instances with public IPs to access the internet.
NAT Gateway (NGW) allows instances with no public IPs to access the internet.
This is a good article to help you understand and solve your problem:
https://medium.com/awesome-cloud/aws-vpc-difference-between-internet-gateway-and-nat-gateway-c9177e710af6