Network ACLs with the Return Rules They Need
Network ACLs are stateless, which is why most of them do not work: the reply to an allowed outbound connection is a new inbound packet nothing lets in. This generates the matching ephemeral-range rule for every TCP and UDP allow.
Verification
Live-testedReally deployed to a cloud sandbox, verified against its outputs and assertions, then destroyed - with the teardown confirmed.
Conformance
- Static validation (fmt · validate · tflint)
- Security scan clean (Checkov)
- Plan test superseded by live test
Provenance
- SHA-256 checksum
- Signature (pending)
Functional
- Live-tested on registry.opentofu.org/hashicorp/aws - applied, verified, destroyed
Last verified 2026-10-31 · tofu 1.12.1 · how we verify
Use it from the registry
terraform · opentofumodule "network_acl" {
source = "www.iac-bazaar.com/iac-bazaar/aws-network-acl/aws"
version = "1.0.0"
}Needs a registry token from /account/tokens. The module itself is free; the account is what identifies you. Full setup: registry docs.
Cite it in your README
badge · attributionPaste this beside the module in the repository that uses it. The badge is rendered from this artifact's verification record, so it reads live-tested because the record says so, and the link lands on this page.
[](https://www.iac-bazaar.com/catalog/aws-network-acl?utm_source=syndication&utm_medium=readme&utm_campaign=artifact)
Terraform module 1.0.0, live-tested on IaC Bazaar: [Network ACLs with the Return Rules They Need](https://www.iac-bazaar.com/catalog/aws-network-acl?utm_source=syndication&utm_medium=readme&utm_campaign=artifact)
```hcl
module "network_acl" {
source = "www.iac-bazaar.com/iac-bazaar/aws-network-acl/aws"
version = "1.0.0"
}
```Preview:
Inputs & outputs
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Documentation
aws-network-acl
A network ACL, its rules, and the return-traffic rules a stateless filter
needs. Works with Terraform and OpenTofu (>= 1.6), AWS provider
>= 6.0, < 7.0.
Network ACLs are stateless, and that is the cause of essentially every one that "does not work". The reply to an allowed outbound connection is a new inbound packet - from the destination's port, to an ephemeral port on the client - and nothing lets it in unless a rule says so. Allow 443 outbound, forget ports 1024-65535 inbound, and the handshake completes in one direction and nothing ever comes back.
So this module generates the matching return rule for every TCP and UDP
allow rule: opposite direction, ephemeral range, same peer, at
number + return_rule_offset. return_traffic = false turns it off where you
mean strictly one-way, and denies and ICMP never get one. The
generated_return_rules output lists them by name - if it is empty and you
expected replies, nothing is letting them back in.
Attaching a custom ACL to a subnet is an instant outage if the rules are not
there yet. A custom ACL denies everything until told otherwise, unlike the
default one which allows everything. The subnet associations are their own
resource and depends_on the rules, so within a single apply the ACL is
populated before any subnet moves onto it.
Other things the module refuses rather than lets you discover:
- Two rules at the same number in the same direction - AWS keeps whichever was written last, and the plan shows no conflict at all
- A rule number of 32767, which is the implicit deny
- A rule with both or neither of
cidr_blockandipv6_cidr_block - A TCP or UDP rule with no ports
Rules are evaluated lowest number first and first match wins, so a broad allow at 100 makes a narrow deny at 200 unreachable. The example leaves gaps of 100 for that reason.
Verification
Static validation runs tofu fmt, init, validate, tflint and checkov.
This module has not yet had a live test, so it is published as statically
validated with its live test pending and does not carry the live-tested mark.
Usage code & full reference need an account
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- One suppressed policy, and why
- Usage
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