I have read articles describing placing a public facing web server in a public subnet and placing application servers in a private subnet. Furthermore, using a NAT Gateway to allow servers in a private subnet to communicate with the Internet, etc.
Alternatively, is it acceptable to also place your web server in the private subnet and flow all Internet traffic through the NAT Gateway?
If the webserver's in the private subnet, it won't be reachable from the Internet. NAT gateways give instances outgoing access, not incoming.
However, you can have webservers in a private subnet, and serve them via an Elastic Load Balancer placed in a public subnet.
Related
I have an application hosted on an EC2 instance in public subnet. To integrate this app with a partner we need to whitelist public IP address of the EC2 instance on partner's firewall.
I want to configure auto-scaling of the application in such a way that outgoing traffic for my application's EC2 instances should be from same single IP address that only needs to be whitelisted on partner's end.
For a private subnet, I know that a NAT Gateway is a solution.
But for instances in a Public Subnet, how this can be achieved? any solution/suggestions will be highly appreciated.
All traffic from the instances will need to be redirected to send via a single resource, such as a proxy or a Gateway.
The simplest solution is as you stated -- configure the subnet to route all Internet-bound traffic to a NAT Gateway or a NAT Instance. All traffic from that instance will then come from a single IP address.
However, configuring the subnet in this way will mean that it is no longer a "public subnet", since a public subnet has Internet-bound traffic sent through an Internet Gateway rather than a NAT. So, it's actually the same as using a private subnet as you suggested in your question.
The only way to do it in a Public Subnet would be to specifically configure your apps to send requests via a proxy server, which would act in a similar way to a NAT Gateway/Instance.
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.
Hope you are all doing good.
AWS allows us to attach a private subnet (created in a Customer VPC) with a route table having route to the internet via internet gateway. Does it make any difference to the instance launched in the private sub-net? or it is as good as having the private subnet not linked to the route table having route to the internet
Regards
AJ
A subnet is not private if it has routes to/from the internet. The instances launched in a private subnet cannot access the internet and cannot be reached from the internet.
For e.g if you have a database instance and you don't want anyone but the instances to access the instance, you can launch the instance in the private subnets.
Also if you want the instances in the private subnet to access internet, you need to setup a Nat Gateway (or a Nat Instance)
Hope this helps
First, we need to know what's the difference between a public subnet and a private subnet.
Public Subnet means this subnet has an Internet Gateway attached to it.
Private Subnet means this subnet has a NAT Gateway attached to it.
And the Internet Gateway can have both inbound and outbound but the NAT only can have outbound to the Internet.
And A NAT will be built in a public subnet but attach to a private subnet.
You can have lots of public/private subnets at the same time and attached NAT or IGW for them, but the IGW only can have one in each VPC.
In some use cases, we will not attach any kinds of NAT and IGW for a subnet. that's because it might be a database subnet and won't expect it to communicate with the Internet.
Normally, we will use a subnet with NAT attached for our application such as EC2 or ECS, Internal Load Balancers.
On the other hand, we will use a subnet with IGW attached for Internet-facing Load balancers, Nginx, Apache.
AWS VPC Design:
https://aws.amazon.com/tw/answers/networking/aws-single-vpc-design/
I think the hidden magic here is that the instance in the private subnet needs a public IP to communicate with outside, we never ever think this an issue in our lives. When our computer connect to the router, it get access to internet without any issue, why it works so smoothly? All because the router handles everything for us, including allocating a private IP for us, making recursively DNS query for us, and the most important, translating the private IP using the router's public IP so that our computer can communicate with the outside bidirectionally.
Let's go back to this AWS VPC scenario, you attached a route table with a default route to the Internet Gateway to your private subnet, which makes it looks like a public subnet. However, the instances still have no public IPs, and, not like our router, the Internet Gateway of AWS VPC doesn't do NAT works! So how can an instance with no public IP and no NAT access the internet? It's impossible.
Anyone here that have a ec2 instance that is on a private subnet in AWS that is able to connect to outside FTP server? It seems that my ec2 instance cannot connect to 3rd party ftp servers without moving to public subnet and using elastic/public ip.
Private subnet by default have no connectivity to outside world or internet. But there is a resource called NAT Gateway that you can configure in your VPC to provide an outgoing internet connectivity from your private subnets.
You can use a network address translation (NAT) gateway to enable
instances in a private subnet to connect to the internet or other AWS
services, but prevent the internet from initiating a connection with
those instances.
You can follow the link here to setup the NAT gateway.
https://aws.amazon.com/premiumsupport/knowledge-center/nat-gateway-vpc-private-subnet/
Private subnets do not have internet connectivity by default. You need to create a nat gateway on the public subnet. Nat gateways are bit expensive. You can also create a nat instance in that case.
What is the best practice to place web app server in AWS VPC? In Private subnet with ELB or Public subnet?
As per my understanding the best practice is to place web app server in public subnet.
Do not place the web server in the public subnet. Launch them in a private subnet and front end them with ELB that runs in a public subnet. You do not want to deal with DDoS attacks on your web server, leave that to ELB which does an excellent job in addition to load balancing.
See:
How do I connect a public-facing load balancer to EC2 instances that have private IP addresses?
Scenario 2: VPC with Public and Private Subnets (NAT)