I am wondering why do we attach an Elastic IP address to a NAT Gateway, but we do not attach one to an Internet Gateway.
The functionality of these two services is very similar. The NAT Gateway allows instances in my private network to initiate communication to the outside. The Internet Gateway extends this by allowing external devices to initiate communication also to the inside. So I would expect the Internet Gateway to require an Elastic IP address too at least, but this does not match the reality.
Is there any explanation to this?
A NAT Gateway still uses an Internet Gateway to access the Internet. So they are not two exclusive, separate things like you indicate in your question. Also, an Internet Gateway is not just for allowing inbound connections from the Internet, as you state in your question, it is for allowing any Internet access inbound to your VPC or outbound from your VPC.
An Internet Gateway allows anything in the VPC with a public IP address to access the Internet. It's basically a bridge between your private network, and Amazon's Internet connection.
A NAT Gateway is one of those resources that gets a public IP address in order to access the Internet through the Internet Gateway. The NAT Gateway just serves as a route to the Internet for all the resources in the VPC that do not have a public IP address.
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So AWS has both kind of facility, but I realised NAT is still dependent on IGW. So many questions are there which I haven't been able to get answers for.
Why does NAT gateway have to be in public subnet? I think on cloud network is implemented by virtual nodes. So why couldn't it be for NAT gateway to act like router in a private subnet, to do NAT when destination address is outside the private network it is also part of?
Why does NAT gateway still require traffic of public subnet it has to be part of to be routed to internet gateway by a route table of same subnet? I mean, NAT gateway should be sufficient in itself to get that traffic gone to internet by being part of some public subnet already. Why does this IGW association with NAT gateway have to be done manually?
An Internet Gateway is a logical connection between a VPC and the Internet. If there is no Internet Gateway, then the VPC has no direct access to the Internet. (However, Internet access might be provided via a Transit Gateway, which itself would need an Internet Gateway.)
Think of the Internet Gateway as the wire that you use to connect your home router to the Internet. Pull out that wire and your home network won't be connected to the Internet.
A subnet is a 'public subnet' if it has a Route Table that references an Internet Gateway.
A NAT Gateway receives traffic from a VPC, forwards it to the Internet and then returns the response that was received. It must live in a public subnet because it needs to communicate with the Internet (and therefore needs a route to the Internet Gateway).
Resources in a private subnet (which, by definition, cannot route to the Internet Gateway) will have their Internet-bound requests sent to the NAT Gateway (due to a Route Table configuration). The NAT Gateway will then forward that request to the Internet and return the response that was received from the Internet.
NAT Gateways exist because organizations want the additional security offered by private subnets, which guarantee that there is no inbound access from the Internet. Similar security can be provided with a Security Group, so private subnets aren't actually required. However, people who are familiar with traditional (non-cloud) networking are familiar with the concept of public and private subnets, so they want to replicate that architecture in the cloud. Physical network routers only apply rules at the boundary of subnets, whereas Security Groups can be applied individually to each Resource. It's a bit like giving each resource its own router.
A NAT Gateway is not very complex. In fact, you can run a NAT instance on Amazon EC2 that does a similar job. Simply launch an Amazon EC2 instance and run this script:
sudo sysctl -w net.ipv4.ip_forward=1
sudo /sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo yum install iptables-services
sudo service iptables save
A NAT Gateway is a bit more sophisticated in that it automatically scales based on the traffic being served and will automatically redeploy any failed infrastructure. It is, effectively, a "managed, auto-scaled NAT instance".
You are right that all of the above is implemented as a virtual network. There is no physical device called an Internet Gateway or a NAT Gateway. Much of it is logical routing, although the NAT Gateway does involve launching infrastructure behind-the-scenes (probably on the same infrastructure that runs EC2 instances). The NAT Gateway only connects to one VPC -- it is not a 'shared service' like Amazon S3, which is available to many AWS users simultaneously.
You also mention performing work 'manually'. An entire VPC (including subnets, route tables, Internet Gateway, NAT Gateway, Security Groups) can be deployed automatically using an AWS CloudFormation template, or via the VPC Wizard in the VPC management console.
I have a Fargate service with one task. From this task I have to interact with a SFTP server managed by an other company, and they need to whitelist my IP.
I've already set a NLB to have a static inbound IP and it's working great, but now I need my outbound IP to static too.
I've read similar questions and they proposed the use of a NAT gateway but it's not working so far.
I have created the NAT gateway, associated it with an Elastic IP and the subnet which hosts the service but it's not working, the outbound IP is still the dynamically allocated one.
What extra steps am I missing?
I have created the NAT gateway, associated it with an Elastic IP and
the subnet which hosts the service
The NAT Gateway needs to be in a public subnet (a subnet with an Internet Gateway attached).
The service needs to be in a private subnet (a subnet with no Internet Gateway, and a route to the NAT Gateway).
The service needs "Assign Public IP" set to false.
Say I have an ec2 in a private subnet with access to the internet through a NAT Gateway and I have VPC endpoints (PrivateLink) for AWS services like DynamoDB or SNS. If my ec2 instance needs to interact with those services, it will use the private link or the NAT Gateway? In other words, the traffic will go on the public internet or will stay inside the VPC?
In other words, the traffic will go on the public internet or will stay inside the VPC?
It will go to interface endpoint. And the reason is that aws chooses more specific (longest prefix match) route when there is more than one choice where to direct traffic. So if VPC has to decide between 0.0.0.0/0 for NAT and interface endpoint address, interface endpoint will be prioritized.
You can easily check it yourself. Place interface endpoint in your private subnet which has route to NAT. Then black all incoming traffic to the interface endpoint using its security group. What you should see is that you are unable to access the service of the interface endpoint, even though there is NAT gateway.
Im working on building up my network which consists of a subnet in a VPC and three instances in the subnet. I have an elastic IP on one of the instances and no public ip or DNS on the others. For the purpose of the other instances reaching the internet for things like windows updates, is it possible to associate a public IP with the internet gateway on the VPC so all of the instances can reach the internet through one IP and for incoming traffic it would all be routed to Instance 1 only on a certain port. In our office now we have a server with multiple vlans all communicating to the internet with one public IP and i am trying to replicate this.
Thanks in advance for the help!
I did some searching before writing out the whole answer and found this write up that should help give you an idea on the distintion between an internet gateway and a Nat gateway. This will help with what you're trying to accomplish:
AWS VPC - Internet Gateway vs. NAT
As other have posted: using a NAT gateway is the best option here since instances with private ips will be able to connect to the internet.
If you do have instances that are "public" ie with and EIP and others that should be private, I would recommend this architecture as laid out in the vpc guides on aws:
https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Scenario2.html
This will give you a good logical separation between public and private servers since they will be within their own subnet.
NAT Gateway might be able to solve this for you.
You need to split your design into "public" and "private" subnets.
Create a new subnet. In this subnet add a NAT Gateway. Add a default route to the NAT Gateway. Then move the instances that you want private into the private subnet.
For the public subnet, just have the instances that you want to be public on the Internet.
The other suggestions about adding a NAT Gateway to your existing subnet won't work. You would need two default routes (one for the Internet Gateway and the other for the NAT gateway).
Keep in mind that the Internet Gateway is a special type of NAT Gateway. This is why you should not have have both in the same subnet (not without knowing what you are doing with route tables in both the VPC and the instances).
We're setting up an Amazon VPC in which we will provision (for now) a single EC2 instance and one RDS instance. This is to 'extend our data center', and should only be using private subnet(s).
So actually, we have this setup, and it is working well (insert smiley face icon). For all intents and purposes, we're mirroring the VPC scenario 4 outlined by Amazon here: http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Scenario4.html
tl;dr: A single VCP, with a VPN connecting to our corporate network. The VPN uses a Virtual Private Gateway (VPC end) and Customer Gateway (our end) to allow us access as necessary to the EC2, which contains a webserver connecting to the RDS instance as needed. Anyone on our network has access to the web server running on the EC2 via a URL. All this is working as expected.
The problem comes when the EC2 instance needs to access a resource on the Internet - The idea is for us to NOT have any public subnets, but to route all traffic from the EC2 instance through our VPN and out the 'standard' path of our corporate Internet access. However we're having trouble setting this up.
The fact that it can be done is hightlighted in Amazon's FAQ here:
https://aws.amazon.com/vpc/faqs/
Q. How do instances without public IP addresses access the Internet?
Instances without public IP addresses can access the Internet in one of two ways:
Instances without public IP addresses can route their traffic through a NAT gateway or a NAT instance to access the Internet. These instances use the public IP address of the NAT gateway or NAT instance to traverse the Internet. The NAT gateway or NAT instance allows outbound communication but doesn’t allow machines on the Internet to initiate a connection to the privately addressed instances.
For VPCs with a hardware VPN connection or Direct Connect connection, instances can route their Internet traffic down the virtual private gateway to your existing datacenter. From there, it can access the Internet via your existing egress points and network security/monitoring devices.
We are trying to avoid option #1 as there is a cost involved (along with complexity and security issues). #2 is the perfect resolution for us, but understanding the process to set it up has been eluding us for a while.
Can anyone walk us through what we need to do (or point us to the correct resources) to ensure the EC2 instance* can access the Internet by routing the traffic down the VPN, through our corporate datacenter, and our our existing Internet access point?
* and anything within the private subnet for that matter
If you are using scenario #2, then all there is to do on the AWS end is to ensure that traffic destined for the internet, 0.0.0.0/0 is routed to your Virtual Private Gateway.
Once traffic heads there, it will go to your Customer Gateway, and into your corporate datacenter. It's up to your local IT guys on that end to get Internet-destined traffic heading out, if it's even possible. But at that point, it's no longer an AWS issue.