non-idempotent ec2 module about terraform-aws-ec2-instance

[antonbabenko]

v1.1.0 has been released.

[jn9999]

I am not seeing the same error but terraform wants to create a replacement instance for an instance created with this module. No changes made, just running plan and apply again.

[boldandbusted]

I am seeing what @jn9999 sees: a create/destroy loop. :/

[antonbabenko]

Sorry for the delay in my response.

From what I see there are at least 4 different arguments which can make this module non-idempotent, which is bad:

1. vpc_security_group_ids
2. subnet_id, availability_zone, private_ip - these arguments are optional to allow AWS to create an instance in the default subnet in a default VPC and assign available private IP. It means that this value is not known when Terraform runs and it is marked <computed> (forces new resource).

The problem with vpc_security_group_ids turns out to be in Terraform AWS provider and is rather popular. There are several mentionings:

• hashicorp/terraform-provider-aws#2036
• hashicorp/terraform-provider-aws#2034
• hashicorp/terraform-provider-aws#1993

Proposed solution:

1. Add private_ip and vpc_security_group_ids to ignore_changes lifecycle.
2. Require users to set values for subnet_id explicitly (availability_zone value will be set internally using aws_subnet data source).

These changes should make this module idempotent.

Objections? Comments?

PS: It helps to upvote related issues to increase chances of them being prioritized and fixed.

[jn9999]

The proposed solution sounds good to me since I already set the subnet_id explicitly.

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