The ICMP setting on AWS security group.

ingress {
    protocol    = "icmp"
    cidr_blocks = [""]
    from_port   = 8 # ICMP type number
    to_port     = 0 # ICMP code

If the protocol is ICMP, the from_port is the ICMP type number and to_port is ICMP code.

Reference using ICMP Control Message, the echo request, e.g. ping command, to allow a machine to take a request from outside, type 8 must be opened. When protocol is ICMP, from_port becomes ICMP type number and to_port becomes ICMP code. Since echo request in ICMP type is 8, echo request in ICMP code is 0, therefore, the from_port in this case is 8 and the to_port is 0.

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