Best way to connect AWS EC2 instances for avoid failed connection on ip change

Question

I have four EC2 instances, three of them running api services and another running user interface (UI). The UI instance obtains the data over api calls to another instances. Right now everthing works fine becouse im using the public IP provided for eeach EC2 service for api calling. But, mi cocern is about what happend if the public ip of service change (for any reason)? then miy application go down becouse UI cannot get the data from services. After a little researching i have found that appers to be a solution: use a vpc for connect EC2 instances over private ip (because is static) and associed the UI instance to an Elastic IP (no problem here). Sow, i have some issues:

1) I make a test putting all instances in the same vpc (and sub net) but when I do ping from one to another the pings faild. Its my approach right? or i missing some thing?

2) I read a couple of another options but im not sure what is best: Maybe i have to use an Api Gateway?. Or a NAT Gateway?

3) What is the standar practice to communicate EC2 instances in private way?

Answer 1

1) I make a test putting all instances in the same vpc (and sub net) but when I do ping from one to another the pings faild. Its my approach right? or i missing some thing?

For security reasons, AWS block the ICMP traffic using security group. Please enable Ping traffic (ICMP) in security group from the Ip's you are trying to connect, it's better to allow the entire CIDR block for the VPC for all traffic, will make your life a lot easy. Please make sure you do this in a test Environment only.

2) I read a couple of another options but im not sure what is best: Maybe i have to use an Api Gateway?. Or a NAT Gateway?

Also, as you mentioned that your concern is that the public IP of the Instance will change, (definitely if your Instance stop/starts for any reason), but why don't you use Elastic IP for all of your Instances, that could be on of the solution, but using this approach all of your instances will be exposed to internet, so going with private IP is the best option.

3) What is the standard practice to communicate EC2 instances in private way?

It depends on the use case, if your Instances are in the same vpc no extra configuration is required, you only need to make sure the security groups, Network Access Control List and firewall configuration are correct. In case if your instances are in different VPC, then you can use VPC Peering/Transit gateway.