aws: dual-stack enabled by default with no way to disable

[jrasell]

PR #271 introduced dual-stack configuration for AWS and enables this by default. While this is fine, there is no way to disable dual-stack behaviour. This issue therefore requests a configuration option or way to disable dual-stack; an environment variable for example would be great.

Nomad related issue: hashicorp/nomad#26233

[jimrosenfeld]

This is currently breaking in me-central-1 because the dualstack api endpoint doesn't exist in that region.

$ dig ec2.me-central-1.api.aws

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.amzn2.13.11 <<>> ec2.me-central-1.api.aws
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 25804
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;ec2.me-central-1.api.aws.      IN      A

;; AUTHORITY SECTION:
me-central-1.api.aws.   32      IN      SOA     ns-1036.awsdns-01.org. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400

;; Query time: 11 msec
;; SERVER: 10.215.32.2#53(10.215.32.2)
;; WHEN: Thu Jul 24 20:39:46 UTC 2025
;; MSG SIZE  rcvd: 138

$ dig ec2.us-east-1.api.aws

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.amzn2.13.11 <<>> ec2.us-east-1.api.aws
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6210
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;ec2.us-east-1.api.aws.         IN      A

;; ANSWER SECTION:
ec2.us-east-1.api.aws.  60      IN      A       3.83.171.207

;; Query time: 12 msec
;; SERVER: 10.215.32.2#53(10.215.32.2)
;; WHEN: Thu Jul 24 20:41:21 UTC 2025
;; MSG SIZE  rcvd: 66

[jimrosenfeld]

AWS documentation confirms there is no dualstack endpoint for EC2 in me-central-1.