AWS - Security Groups and Network ACLs
You notice your EC2 instance in the default security group cannot receive inbound traffic from another instance in the same group. What is the most likely cause?
You notice your EC2 instance in the default security group cannot receive inbound traffic from another instance in the same group. What is the most likely cause?
medium📝 Debug Q6 of 15
Step-by-Step Solution
Solution:
Step 1: Recall default inbound behavior of default security group
By default, inbound traffic from instances in the same group is allowed.Step 2: Identify why traffic is blocked
If inbound traffic is blocked, the default inbound rule was likely deleted or changed.Final Answer:
The default security group inbound rule was deleted or modified. -> Option BQuick Check:
Missing inbound rule blocks traffic [OK]
Quick Trick: Check if default inbound rule was changed if traffic blocked [OK]
Common Mistakes:
- Assuming outbound rules block inbound traffic
- Ignoring VPC differences
- Confusing public IP with security group rules
Master "Security Groups and Network ACLs" in AWS
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