[Bug]: 5.5: database host is evaluated to null

[speller]

Terraform Core Version

1.5.0

AWS Provider Version

5.5.0

Affected Resource(s)

No response

Expected Behavior

Working fine

Actual Behavior

I'm using the database host in other configurations. But after the recent release of version 5.5, I got this weird error:

│ Error: Invalid template interpolation value
│ 
│   on main.tf line 154, in locals:
│  154:     {name: "DATABASE_URL", value: "mysql://${local.db_user}:${local.db_password}@${module.db.host}:${module.db.port}/${local.db_name}?serverVersion=8&charset=utf8mb4"},
│     ├────────────────
│     │ module.db.host is null
│ 
│ The expression result is null. Cannot include a null value in a string
│ template.

The module is defined this way:

output "host" {
  value = var.cluster ? aws_rds_cluster.app-db[0].endpoint : aws_db_instance.app-db[0].address
}

resource "aws_db_instance" "app-db" {
  count = var.cluster ? 0 : 1
  apply_immediately = true
  identifier_prefix = local.infra_name_hyphen
  instance_class = var.instance_type
  allocated_storage = var.storage_size
  max_allocated_storage = var.max_storage_size
  storage_type = var.storage_type
  engine = var.engine
  engine_version = local.db_engine_version_full
  parameter_group_name = aws_db_parameter_group.app-db.name
  username = var.user
  password = var.password
  skip_final_snapshot = var.skip_final_snapshot
  db_subnet_group_name = aws_db_subnet_group.db-nets.name
  db_name = var.initial_db_name
  allow_major_version_upgrade = var.allow_major_version_upgrade
  auto_minor_version_upgrade = true
  vpc_security_group_ids = [
    aws_security_group.app-db.id,
  ]
  snapshot_identifier = var.snapshot_id
  delete_automated_backups = var.delete_automated_backups
  backup_retention_period = var.backup_retention_days
  storage_encrypted = true
  enabled_cloudwatch_logs_exports = var.cloudwatch_logs_export
  multi_az = var.multi_az
  tags = {
    Name = local.infra_name_hyphen
    "cost:env" = var.cost_env
    "cost:app" = var.cost_app
  }
  lifecycle {
    create_before_destroy = true
    ignore_changes = [
      snapshot_identifier,
    ]
  }
}

Related plan:

# module.db.aws_db_instance.app-db[0] will be created
  + resource "aws_db_instance" "app-db" {
      + address                               = (known after apply)
      + allocated_storage                     = 10
      + allow_major_version_upgrade           = false
      + apply_immediately                     = true
      + arn                                   = (known after apply)
      + auto_minor_version_upgrade            = true
      + availability_zone                     = (known after apply)
      + backup_retention_period               = 1
      + backup_window                         = (known after apply)
      + ca_cert_identifier                    = (known after apply)
      + character_set_name                    = (known after apply)
      + copy_tags_to_snapshot                 = false
      + db_name                               = "pkg"
      + db_subnet_group_name                  = "redacted"
      + delete_automated_backups              = true
      + enabled_cloudwatch_logs_exports       = [
          + "slowquery",
        ]
      + endpoint                              = (known after apply)
      + engine                                = "mysql"
      + engine_version                        = "8.0"
      + engine_version_actual                 = (known after apply)
      + hosted_zone_id                        = (known after apply)
      + id                                    = (known after apply)
      + identifier                            = (known after apply)
      + identifier_prefix                     = "redacted"
      + instance_class                        = "db.t4g.micro"
      + iops                                  = (known after apply)
      + kms_key=(sensitive)
      + latest_restorable_time                = (known after apply)
      + license_model                         = (known after apply)
      + listener_endpoint                     = (known after apply)
      + maintenance_window                    = (known after apply)
      + master_user_secret=(sensitive)
      + master_user_secret=(sensitive)
      + max_allocated_storage                 = 0
      + monitoring_interval                   = 0
      + monitoring_role_arn                   = (known after apply)
      + multi_az                              = false
      + nchar_character_set_name              = (known after apply)
      + network_type                          = (known after apply)
      + option_group_name                     = (known after apply)
      + parameter_group_name                  = (known after apply)
      + password=(sensitive)
      + performance_insights_enabled          = false
      + performance_insights_kms_key=(sensitive)
      + performance_insights_retention_period = (known after apply)
      + port                                  = (known after apply)
      + publicly_accessible                   = false
      + replica_mode                          = (known after apply)
      + replicas                              = (known after apply)
      + resource_id                           = (known after apply)
      + skip_final_snapshot                   = true
      + snapshot_identifier                   = (known after apply)
      + status                                = (known after apply)
      + storage_encrypted                     = true
      + storage_throughput                    = (known after apply)
      + storage_type                          = "gp2"
      + timezone                              = (known after apply)
      + username                              = "admin"
      + vpc_security_group_ids                = (known after apply)
    }
  # module.db.aws_db_parameter_group.app-db will be created

And it is created with no issues:

module.db.aws_db_instance.app-db[0]: Creation complete after 1m22s [id=db-H35redacted]

Nothing special. I believe this is related to #31594 when the provider decides that the database is ready when it is not ready.

Restarting the same deployment with no changes fixes the issue.

[github-actions]

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[johanneswuerbach]

We ran into the same issue and looking into the terraform state, the status of the created instance is status = "creating", which sounds like there is a bug in the waiting logic and the provide stopped waiting for instances to be available 🤔

In our case the instance was newly created using v5.5.0 and a clean state.

[ewbankkit]

I can reproduce this in our acceptance tests:

% make testacc TESTARGS='-run=TestAccRDSInstance_identifierPrefix\|TestAccRDSInstance_identifierGenerated' PKG=rds
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/rds/... -v -count 1 -parallel 20  -run=TestAccRDSInstance_identifierPrefix\|TestAccRDSInstance_identifierGenerated -timeout 180m
=== RUN   TestAccRDSInstance_identifierPrefix
=== PAUSE TestAccRDSInstance_identifierPrefix
=== RUN   TestAccRDSInstance_identifierGenerated
=== PAUSE TestAccRDSInstance_identifierGenerated
=== CONT  TestAccRDSInstance_identifierPrefix
=== CONT  TestAccRDSInstance_identifierGenerated
=== NAME  TestAccRDSInstance_identifierPrefix
    instance_test.go:188: Step 2/2 error running import: ImportStateVerify attributes not equivalent. Difference is shown below. The - symbol indicates attributes missing after import.
        
          map[string]string{
        + 	"address":        "tf-acc-test-prefix-20230629185347776800000002.cvflxcqblmy1.us-west-2.rds.amazonaws.com",
        + 	"endpoint":       "tf-acc-test-prefix-20230629185347776800000002.cvflxcqblmy1.us-west-2.rds.amazonaws.com:3306",
        + 	"hosted_zone_id": "Z1PVIF0B656C1W",
        - 	"port":           "0",
        + 	"port":           "3306",
        - 	"status":         "creating",
        + 	"status":         "available",
          }
--- FAIL: TestAccRDSInstance_identifierPrefix (425.76s)
--- PASS: TestAccRDSInstance_identifierGenerated (547.74s)
FAIL
FAIL	github.com/hashicorp/terraform-provider-aws/internal/service/rds	552.980s
FAIL
make: *** [testacc] Error 1

[github-actions]

This functionality has been released in v5.6.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.