[Bug]: expanding allowed prefixes aws_dx_gateway_association causes downtime

[marcincuber]

Terraform Core Version

1.4.1

AWS Provider Version

4.58

Affected Resource(s)

• aws_dx_gateway_association
• aws_ec2_transit_gateway_route_table_association

Expected Behavior

When updating aws_dx_gateway_association with an additional allowed_prefix. Gateway association should be updated in-place with zero impact on other prefixes.

Actual Behavior

Update to aws_dx_gateway_association resource causes aws_ec2_transit_gateway_route_table_association replacement which is disabling all the traffic through the dx gateway.

Relevant Error/Panic Output Snippet

No response

Terraform Configuration Files

resource "aws_dx_gateway" "lnd_eng_1" {
  name            = "LDN_IXN_ENG_1"
  amazon_side_asn = "6000"
}

resource "aws_dx_gateway_association" "lnd_eng_1" {
  dx_gateway_id         = aws_dx_gateway.lnd_eng_1.id
  associated_gateway_id = aws_ec2_transit_gateway.main_router.id

  allowed_prefixes = local.dx_gateway_allowed_prefixes
}

resource "aws_ec2_transit_gateway_route_table_association" "dx_gateway_lnd_eng_1" {
  transit_gateway_attachment_id  = data.aws_ec2_transit_gateway_attachment.lnd_eng_1.transit_gateway_attachment_id
  transit_gateway_route_table_id = aws_ec2_transit_gateway_route_table.main_router.id
}

Plan Output

  ~ resource "aws_dx_gateway_association" "lnd_eng_1" {
      ~ allowed_prefixes                    = [
          + "10.10.10.0/23",
            # (4 unchanged elements hidden)
        ]
        id                                  = "ga-46208b72-12345"
        # (6 unchanged attributes hidden)
    }

    # aws_ec2_transit_gateway_route_table_association.dx_gateway_lnd_eng_1 must be replaced
-/+ resource "aws_ec2_transit_gateway_route_table_association" "dx_gateway_lnd_eng_1" {
      ~ id                             = "tgw-rtb-3445_tgw-attach-1234" -> (known after apply)
      ~ resource_id                    = "46208b72-f184-12345" -> (known after apply)
      ~ resource_type                  = "direct-connect-gateway" -> (known after apply)
      ~ transit_gateway_attachment_id  = "tgw-attach-123434" # forces replacement -> (known after apply)
        # (1 unchanged attribute hidden)
    }

Steps to Reproduce

Implement aws_dx_gateway_association which is associated with transit gateway aws_ec2_transit_gateway_route_table_association.dx_gateway

Important Factoids

aws_ec2_transit_gateway_route_table_association.dx_gateway_lnd_eng_1 must be replaced action shouldn't be happening as allowed prefixes can be updated in place.

References

Related docs -> https://docs.aws.amazon.com/directconnect/latest/UserGuide/allowed-to-prefixes.html

Would you like to implement a fix?

None

[github-actions]

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[justinretzolk]

Hey @marcincuber 👋 Thank you for taking the time to raise this! So that we have all of the necessary information in order to look into this, can you supply a sample Terraform configuration that exhibits this behavior?

[marcincuber]

@justinretzolk I updated the issue with sample configuration.

[per-lind]

Any news on this issue? I have the same problem and it makes it really hard to work with the transitgateway together with directconnect.

[sathishsrinu]

@marcincuber - did you find any solution on this?