While creating NAT Gateway an Elastic IP Address is created in AWS. The AWS documentation (1) also mentions the same. Why is an Elastic IP Address required for NAT Gateway?
Simply stated, the EIP is required because that is the way the NAT Gateway feature was engineered.
It wouldn't make sense to have a dynamic address on a NAT device -- if the address changed, that would be guaranteed to break any sessions in progress... and the only way to allocate a static address is by allocating an Elastic IP address (EIP).
It's also common to have external vendors whitelist your servers (for access to their servers) by providing them with the EIP of your NAT Gateway, in which case a dynamic address from the public pool would be unacceptable.
There may also be internal, proprietary reasons related to the way EIPs function that made this requirement a necessity... but that is not documented, so such an assertion would be mere speculation. An example of this: the public pool addresses (like those auto-assigned to EC2 instances configured with a public IP address from the pool, not an EIP) might be engineered to the specific availability zone, or even a subset of a single availability zone (they do, after all, change, when an instance is stopped/started, implying that they might be dedicated to specific server bays within an AZ), while EIPs can migrate anywhere from one zone to another within a region. This strongly implies different internal topologies.
This requirement (constraint?), to me, seems insignificant: you shouldn't be charged for this EIP, and if you need to increase the maximum allowed number of EIPs in a region, you can submit a support request at no charge, describing your use case, to request a limit increase.
The EIP requirement is rather arbitrary. Having a static IP makes coding the NAT easier (it doesn't have to check the WAN Interface for upstream address changes) but NATs that support a dynamic upstream address are very common - almost every home served by a major ISP has one. Sure, there's a risk the external address might change and break the current connections, but the ISPs know this and try hard NOT to change the address. Generally it changes only when you reboot the router, and at that point all your connections are broken anyway.
On AWS there there are many similar scenarios where you don't care if your NAT gateways external address changes, especially if your VPC does not contain any public servers. I have a lot of these, and I'm trying to run them on free accounts - it annoys me that they force me to burn through my short supply of static IPs.
As others observed this is a small expense, and AWS is still way cheaper than any other way I know to get this kind of cloud power; but that EIP is not strictly required.
No insignificant at all, you are only allowed to have 5 EIPs, so having 2 or 3 apps in two availability zones will hit that threshold.
As of June 2021, the AWS NAT Gateway does not require an ElasticIP (if you choose "Private" mode):
A private NAT Gateway, or NAT Gateway with connectivity type set to private, does not require EIP and you do not need to attach an internet gateway with your VPC.
https://aws.amazon.com/about-aws/whats-new/2021/06/aws-removes-nat-gateways-dependence-on-internet-gateway-for-private-communications/
I think what the answers here are missing is that the NAT Gateway (NATG) traffic is still being routed through an Internet Gateway (IGW), which performs static (one private IP to one public IP) NAT. As the image in the question indicates, the Elastic IP (EIP) is an association. It is the IGW that is translating the NATG's private IP to its associated public EIP.
This EIP requirement is therefore consistent from an AWS implementation perspective for any resource (e.g. EC2 instance) in a public subnet accessing the internet through an IGW.
Let's say you have private network instances, how will they connect to internet? That's when NAT comes in. NAT ip is public. And private subnets can be associated with NAT. So in that way, the instance in private subnet can connect to internet using NAT. This is very useful when you have server to whitelist your ip. Just give them the NAT EIP and problem solved.
Related
I'm preparing for AWS Certificate Associate. Have some concept questions about AWS VPC.
For Elastic Network Interfaces (ENI), the main text in the study guide says and I quote:
It’s possible to attach additional ENIs to an instance. Those ENIs may be in a different
subnet, but they must be in the same availability zone as the instance. As always, any
addresses associated with the ENI must come from the subnet to which it is attached.
while in the summary of this chapter, still in study guide says:
Any
additional ENI you attach to an instance must be in the same subnet as the primary ENI.
1.1 Are the bold parts in the above two statements contradictory? Because one says ENIs should be in the same subset while the other says in the same AZ, which one is right?
1.2 How to interpret the relationship between the bold part and the italic part in the first statement? Is it like the ENI can be located in other subnets, but the address should point to the instance that it has been attached to? Sounds kind of weird.
About difference between NAT Gateway and NAT Instance.
The book states NAT Instance can connect to instances that don't have public IP, while NAT Gateway cannot. Just want to clarify, does this "instance" means the destination instance in the Internet, instead of the sourcing instance within VPC? Since the reason to adopt NAT devices (no matter gateway or instance) is because the sourcing instance in private cloud doesn't have public IP?
Thanks!
An instance can have multiple ENIs, each in a different subnet (within the same Availability Zone). I recommend that you try it yourself to confirm. In fact, that is good advice for everything you do in AWS because the Certification is meant to prove that you have the knowledge and experience (rather than just having read a Study Guide).
All you'll need to know about NAT in a VPC is:
A NAT Gateway is a managed service that resides in a single subnet and AZ. An Elastic IP address is assigned to the NAT Gateway and all traffic coming from it to the Internet will 'appear' to be coming from that Elastic IP address.
A NAT Instance is an EC2 instance configured as a NAT. It can be assigned an Elastic IP address, or a normal (random) public IP address.
Again, I highly recommend you create both types, then configure and use them in a VPC. That way, you are actually increasing your own knowledge that would be useful for a future employer (rather than just getting a certification).
I am having trouble understanding this image:
Specifically what I want to have is the Global Accelerator attached to every region, with each region having a VPC and Load Balancer. Then in each AZ in a region, have a public and private subnet. The private subnet or database servers will do all the computation and rendering. The public subnet is the Load Balancer (or does the public subnet need to be a set of instances?).
The public subnet also has an Internet Gateway and NAT Gateway attached. The docs say a private subnet can access the internet using a NAT Gateway in the public subnet, but I don't understand why it doesn't just use the Internet Gateway.
I have a route table in the public subnet, and the private subnet. In the public subnet, the route table goes to 0.0.0.0/0 pointing to the internet gateway. In the private subnet, it goes to 0.0.0.0/0 pointing to the NAT gateway.
There are also an Elastic IP associated with the NAT Gateway, presumably so that's what the internet sees when I make a request from a private server.
My question is, what is connected to what? The docs aren't clear enough on a practical example. I would like to have a public subnet, which I think doesn't require having any instances (am I wrong?), only the load balancer. Then the private subnet is the computation/database subnet which does consist of instances which can only connect to the internet through the load balancer connected to the NAT gateway.
I am confused. I have read the docs over and over again but still don't see how this is supposed to be wired up. Any help explaining what is connected to what in this diagram (extending it to include the Global Accelerator) would be greatly appreciated.
Please don't take this the wrong way, but I don't think you really need everything you are saying that you want.
I would recommend that you start with one region and no Global Accelerator. Implement your system and either creating a test platform that can simulate user traffic, or release your system to your customers and monitor it to determine performance.
If you run in multiple regions, you have a problem with where to keep your data -- data might be kept separate in each region, or replicated. This all depends upon your needs. I suggest you start simple, then expand if you need to operate differently.
Global Accelerator does not make sense when using multiple regions, since it is designed to send traffic to one location. Instead, consider Amazon CloudFront to cache data closer to your customers to provide better performance.
If your application runs on multiple web servers, put a Load Balancer in public subnet(s) and everything else in private subnet(s).
Put simply, start simple. Get your application working in the simplest possible way. Then, if you have greater requirements (eg low latency to users), look at adding Amazon CloudFront. Very few applications span multiple regions, so make that choice carefully and have a specific reason for doing so.
When you use AWS Global Accelerator, you can keep your ALB and instance private, without exposing them to the internet.
Such architecture is explained in the recent AWS blog post:
Accessing private Application Load Balancers and EC2 instances through AWS Global Accelerator
In this architecture, internal ALB is used, and there are no public subnets. The only requirements is the pretense of internet gateway in the VPC. It should be noted, that even though there is internet gateway, no routes are configured for the subnets to access the internet:
To avoid internet traffic from inadvertently flowing into a private subnet, we require that an internet gateway is attached to the VPC that contains resources when a client address-preserving accelerator is created.
I came in late but:
One rule is "if it can stay in private subnet then keep it in private subnet". Accessing the internet will always be costlier. When that is done if you must reach the internet then use VPC endpoints (if possible) instead of NATG and IGW. Endpoints are cheaper and make cheaper data transfers.
For Accelerator and Cloudfront, if data cacheing will be a pain for you then use Accelerator, if not, simply put, CloudFront is cheaper and better.
Despite all this, your architecture and use case will always decide your best and cheapest set up.
I am not an expert in networking, so I want to get a clearer image. I have an AWS running instance, and its local network is 172.31.16.0/20 with address. I know that Amazon uses 172.31.0.0/16 CIDR to manage private addresses.
If someone does a scan on 172.31.0.0/16, could he/she discover my instance?
I tried to do it with another instance of mine and it detects it, but I am not sure if it works, for instance, I don't own because of this notion of VPC that I don't really understand.
Simply no. This CIDR is for a VPC, and your VPC is different from another AWS user's VPC.
To allow another AWS user to access your VPC network, you need to share it manually, so if you do not share it, it is not possible for other users to detect your instance by a brute force query.
For public IP addresses, you definitely can be discovered.
For intern IP addresses, to the extent I know, it is a virtual network, and it is isolated from other VPCs.
Traffic for private RFC1918 addresses is not routable over the Internet. No one can hit your 172.31 address across the Internet. Not from outside AWS and not from another VPC (yours or anyone else's).
VPCs are per account and are isolated from each other. You can, however, share subnets of your VPC with another AWS account within the same AWS Organization, if you choose to. You can also peer VPCs, if you choose to.
Other instances within your VPC can reach an instance in the same VPC, of course, assuming the default routing and NACLs, as can anyone on your VPC's extended network, for example if you have a VPN connection into your VPC (but I assume that's not relevant here).
We are trying to use Elastic Load Balancing in AWS with auto-scaling so we can scale in and out as needed.
Our application consists of several smaller applications, they are all on the same subnet and the same VPC.
We want to put our ELB between one of our apps and the rest.
Problem is we want the load balancer to be working both internally between different apps using an API and also internet-facing because our application still has some usage that should be done externally and not through the API.
I've read this question but I could not figure out exactly how to do it from there, it does not really specify any steps or maybe I did understand it very well.
Can we have an ELB that is both internal and external?
For the record, I can only access this network through a VPN.
It is not possible to for an Elastic Load Balancer to have both a public IP address and a private IP address. It is one or the other, but not both.
If you want your ELB to have a private IP address, then it cannot listen to requests from the internet.
If your ELB is public-facing, you can still call to it from your internal EC2 instances using the public endpoint. However, there are some caveats that goes with this:
The traffic will exit your VPC and re-enter it. It will not be direct instance-to-ELB connection that a private IP address will afford you.
You also cannot use security groups in your security group rules.
There are 3 alternative scenarios:
Duplicate the ELB and EC2 instances, one dedicated to private traffic, one dedicated to public traffic.
Have 2 ELBs (one public, one private) that share the same back-end EC2 instances.
Don't use an ELB for either private or public traffic, and instead use an Elastic IP address (if public) or a private IP address (if private) on a single EC2 instance.
I disagree with #MattHouser answer. Actually, in a VPC, your ELB have all its internal interfaces listed in Network Interfaces with Public IP AND Primary private IP.
I've tested the private IP of my public ELB and it's working exactly like the external one.
The problem is : theses IPs are not listed anywhere in a up to date manner like on a private ELB DNS. So you have to do it by yourself.
I've made a little POC script on this, with an internal Route53 hosted zone : https://gist.github.com/darylounet/3c6253c60b7dc52da927b80a0ae8d428
I made a Lambda function that checks which private IPs are set to the loadbalancer and will update Route53 record when it changes: https://github.com/Bramzor/lambda-sync-private-elb-ips
Using this function, you can easily make use of the ELB for private traffic. I personally use it to connect multiple regions to each other over a VPC inter-region peering without needing an additional ELB.
The standard AWS solution would be to have an extra internal ELB for this.
Looks like #DaryL has an interesting workaround, but it could fail for 5 minutes if the DNS is not updated. Also there is no way to have a separate security group for the internal IPs since they share the ENI and security of the external IP of the ELB.
I faced the same challenge and I can confirm the best solution so far is to have two different ALBs, one internet-facing and the other internal. You can attach both ALBs to a single AutoScaling Group so you can access the same cluster.
Make sure the networking options (Subnets, security groups) of both ALBs are the same in order for both to access the same cluster instances. Autoscaling and Launch Configuration works seamlessly with both ALBs attached to the same AutoSacling Group. This is also working with ALBs created from ElasticBeanstalk environments.
Bit of an odd question about AWS + ELBs.
We have a VPC that contains public and private subnets. Within the private subnets, we have 2 applications (application 1 and application 2) deployed using ASGs, and each is reachable by it's own public ELB.
Application 1 also needs to talk to application 2, one is a website and the other is an API service. I was just wondering if I needed to setup an internal ELB for application 2 given that I already have a public ELB for it?
If it makes a difference, all the instances communicate with the outside world using a NAT. Is AWS clever enough to route the traffic internally, or will it go out and back in? If the latter, it definitely feels like I should add an internal ELB.
Cheers
AWS will not do anything in this case to optimize the routing. To do so would require either manipulating the DNS responses into private addresses or defeating/bypassing your routing table configuration, neither of which would probably be desirable in many cases. It would also have implications for security groups.
Using an external ELB from inside, the traffic will go out the NAT instance and hit a public IP of the external load balancer. Additionally, you'll pay for that traffic to leave the network and come back, at $0.01 per gigabyte transferred, billed against each side of the connection (that is, the NAT instance and the ELB would both be billed $0.01 for the same gigabyte of data transferred between them = $0.02/GB) in most configurations.
http://aws.amazon.com/ec2/pricing/