EC2s in an Autoscaling group across 2 subnets in same VPC can't connect to each other

Hi, you may have an issue in the configuration of the route tables associated to your subnets. Each of them has its own routing table which must contain a route to the other subnet.

See https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Route_Tables.html

Your VPC has an implicit router, and you use route tables to control where network 
traffic is directed. Each subnet in your VPC must be associated with a route table, 
which controls the routing for the subnet (subnet route table). You can explicitly 
associate a subnet with a particular route table.

Best,

Didier

Hi,

Could you please verify the following in the NACL and route table attached to your subnet?

• NACL - Allows all traffic or relevant ports/protocols in both inbound and outbound
• Route Table - Allows traffic to the VPC or subnets

Additionally, the document you shared, mentions enabling the firewall in the instances. Assuming you did this could you try disabling the firewall and try connecting to test if the issue is related to the firewall rules?

Does the SG for the EC2 instance you're pinging from have an outbound (egress) rule allowing Ping? Also you said you opened all ports but is that just TCP ports? You need ICMP for Ping.