fix: Avoid error looking up tgw_route_table when resource is not crea…

[gmherb]

Description

When sharing a tgw across aws accounts (tgw_share=true and tgw_create=false), the module runs into an error when looking up the transit gateway route table. By introducing a local variable with 'try' we can circumvent the issue.

Motivation and Context

Module fails when trying to share across accounts. Previous issues reported:
#61
#46
#47
#56

Breaking Changes

none

[ndobbs]

Looks like this PR solves the issues I'm running into as well.

terraform_version: v1.1.7
module_version: v2.5.1

[cryptk]

I'm hitting this now as well trying to do a cross-account TGW attachment. I hate to be a pest, but @antonbabenko is there any chance we can get a 2.5.2 released with this fix in it?

[bryantbiggs]

we should be able to do:

Suggested change

	transit_gateway_route_table_id = coalesce(lookup(each.value, "transit_gateway_route_table_id", null), local.tgw_route_table_id)
	transit_gateway_route_table_id = var.create_tgw ? aws_ec2_transit_gateway_route_table.this[0].id : try(each.value.transit_gateway_route_table_id, var.transit_gateway_route_table_id)

[bryantbiggs]

actually, this won't solve the issue either. Please see PR #68 and let me know if this resolves the issue

[bryantbiggs]

ignore - this won't work either

[bryantbiggs]

and same as above

Suggested change

	transit_gateway_route_table_id = coalesce(lookup(each.value, "transit_gateway_route_table_id", null), local.tgw_route_table_id)
	transit_gateway_route_table_id = var.create_tgw ? aws_ec2_transit_gateway_route_table.this[0].id : try(each.value.transit_gateway_route_table_id, var.transit_gateway_route_table_id)

[bryantbiggs]

ignore - this won't work either

[bryantbiggs]

hey all, would anyone be willing to double check PR #68 and let me know if this resolves the issue? The proposed changes here won't work either because doing try(var.some_variable, ....) will always succeed and take var.some_variable. It will only fail if you do a lookup on an attribute/value that doesn't exist. For example, these all will fail the first try() check and continue down the chain (resulting in null in these examples):

• try(var.foo.bar, null) if var.foo doesn't contain bar in its map attributes
• try(aws_some_resource[0].id, null) if aws_some_resource` is not created
• try(each.value.foo, null) if the map that is being looped over with for_each doesn't contain foo in its attributes

[antonbabenko]

This issue has been resolved in version 2.6.0 🎉

[github-actions]

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