Cluster is recreated with every apply

[nodomain]

This is linked to hashicorp/terraform#16724 and might be fixed by #35

Currently a terraform plan shows that the RDS cluster is recreated with every apply, the cause seems to be a wonky availability-zones attribute.
Somehow this seems to trigger a new resource. See plan output.

-/+ module.rds_cluster_aurora_mysql.aws_rds_cluster.default (new resource required)
      id:                                  "namespace-stage-project" => <computed> (forces new resource)
      apply_immediately:                   "true" => "true"
      arn:                                 "arn:aws:rds:eu-central-1:123456789:cluster:namespace-stage-project" => <computed>
      availability_zones.#:                "3" => "2" (forces new resource)
      availability_zones.1126047633:       "eu-central-1a" => "eu-central-1a"
      availability_zones.2903539389:       "eu-central-1c" => "" (forces new resource)
      availability_zones.3658960427:       "eu-central-1b" => "eu-central-1b"
      backup_retention_period:             "5" => "5"
      cluster_identifier:                  "namespace-stage-project" => "namespace-stage-project"
      cluster_identifier_prefix:           "" => <computed>
      cluster_members.#:                   "2" => <computed>
      cluster_resource_id:                 "cluster-AAAXXXX" => <computed>
      database_name:                       "project" => "project"
      db_cluster_parameter_group_name:     "namespace-stage-project" => "namespace-stage-project"
      db_subnet_group_name:                "namespace-stage-project" => "namespace-stage-project"
      endpoint:                            "namespace-stage-project.cluster-sensitive.eu-central-1.rds.amazonaws.com" => <computed>
      engine:                              "aurora-mysql" => "aurora-mysql"
      engine_mode:                         "provisioned" => "provisioned"
      engine_version:                      "5.7.12" => <computed>
      final_snapshot_identifier:           "namespace-stage-project" => "namespace-stage-project"
      hosted_zone_id:                      "Z1RLSENSITIVE" => <computed>
      iam_database_authentication_enabled: "false" => "false"
      kms_key_id:                          "arn:aws:kms:eu-central-1:123456789:key/xxx" => <computed>
      master_password:                     <sensitive> => <sensitive> (attribute changed)
      master_username:                     "project" => "project"
      port:                                "3306" => <computed>
      preferred_backup_window:             "07:00-09:00" => "07:00-09:00"
      preferred_maintenance_window:        "wed:03:00-wed:04:00" => "wed:03:00-wed:04:00"
      reader_endpoint:                     "namespace-stage-project.cluster-ro-sensitive.eu-central-1.rds.amazonaws.com" => <computed>
      skip_final_snapshot:                 "false" => "false"
      storage_encrypted:                   "true" => "true"
      tags.%:                              "3" => "3"
      tags.Name:                           "namespace-stage-project" => "namespace-stage-project"
      tags.Namespace:                      "namespace" => "namespace"
      tags.Stage:                          "stage" => "stage"
      vpc_security_group_ids.#:            "1" => "1"
      vpc_security_group_ids.636648702:    "sg-080d3cfa4609edea8" => "sg-080d3cfa4609edea8"

-/+ module.rds_cluster_aurora_mysql.aws_rds_cluster_instance.default[0] (new resource required)
      id:                                  "namespace-stage-project-1" => <computed> (forces new resource)
      apply_immediately:                   "" => <computed>
      arn:                                 "arn:aws:rds:eu-central-1:123456789:db:namespace-stage-project-1" => <computed>
      auto_minor_version_upgrade:          "true" => "true"
      availability_zone:                   "eu-central-1a" => <computed>
      cluster_identifier:                  "namespace-stage-project" => "${aws_rds_cluster.default.id}" (forces new resource)
      db_parameter_group_name:             "namespace-stage-project" => "namespace-stage-project"
      db_subnet_group_name:                "namespace-stage-project" => "namespace-stage-project"
      dbi_resource_id:                     "db-SENSITIVE0" => <computed>
      endpoint:                            "namespace-stage-project-1.sensitive.eu-central-1.rds.amazonaws.com" => <computed>
      engine:                              "aurora-mysql" => "aurora-mysql"
      engine_version:                      "5.7.12" => <computed>
      identifier:                          "namespace-stage-project-1" => "namespace-stage-project-1"
      identifier_prefix:                   "" => <computed>
      instance_class:                      "db.t2.small" => "db.t2.small"
      kms_key_id:                          "arn:aws:kms:eu-central-1:123456789:key/xxx" => <computed>
      monitoring_interval:                 "0" => "0"
      monitoring_role_arn:                 "" => <computed>
      performance_insights_enabled:        "false" => <computed>
      performance_insights_kms_key_id:     "" => <computed>
      port:                                "3306" => <computed>
      preferred_backup_window:             "07:00-09:00" => <computed>
      preferred_maintenance_window:        "mon:04:25-mon:04:55" => <computed>
      promotion_tier:                      "0" => "0"
      publicly_accessible:                 "false" => "false"
      storage_encrypted:                   "true" => <computed>
      tags.%:                              "3" => "3"
      tags.Name:                           "namespace-stage-project" => "namespace-stage-project"
      tags.Namespace:                      "namespace" => "namespace"
      tags.Stage:                          "stage" => "stage"
      writer:                              "false" => <computed>

-/+ module.rds_cluster_aurora_mysql.aws_rds_cluster_instance.default[1] (new resource required)
      id:                                  "namespace-stage-project-2" => <computed> (forces new resource)
      apply_immediately:                   "" => <computed>
      arn:                                 "arn:aws:rds:eu-central-1:123456789:db:namespace-stage-project-2" => <computed>
      auto_minor_version_upgrade:          "true" => "true"
      availability_zone:                   "eu-central-1b" => <computed>
      cluster_identifier:                  "namespace-stage-project" => "${aws_rds_cluster.default.id}" (forces new resource)
      db_parameter_group_name:             "namespace-stage-project" => "namespace-stage-project"
      db_subnet_group_name:                "namespace-stage-project" => "namespace-stage-project"
      dbi_resource_id:                     "db-SENSITIVE1" => <computed>
      endpoint:                            "namespace-stage-project-2.sensitive.eu-central-1.rds.amazonaws.com" => <computed>
      engine:                              "aurora-mysql" => "aurora-mysql"
      engine_version:                      "5.7.12" => <computed>
      identifier:                          "namespace-stage-project-2" => "namespace-stage-project-2"
      identifier_prefix:                   "" => <computed>
      instance_class:                      "db.t2.small" => "db.t2.small"
      kms_key_id:                          "arn:aws:kms:eu-central-1:123456789:key/xxx" => <computed>
      monitoring_interval:                 "0" => "0"
      monitoring_role_arn:                 "" => <computed>
      performance_insights_enabled:        "false" => <computed>
      performance_insights_kms_key_id:     "" => <computed>
      port:                                "3306" => <computed>
      preferred_backup_window:             "07:00-09:00" => <computed>
      preferred_maintenance_window:        "sun:03:45-sun:04:15" => <computed>
      promotion_tier:                      "0" => "0"
      publicly_accessible:                 "false" => "false"
      storage_encrypted:                   "true" => <computed>
      tags.%:                              "3" => "3"
      tags.Name:                           "namespace-stage-project" => "namespace-stage-project"
      tags.Namespace:                      "namespace" => "namespace"
      tags.Stage:                          "stage" => "stage"
      writer:                              "true" => <computed>

Config:

module "rds_cluster_aurora_mysql" {
  source             = "git::https://github.com/cloudposse/terraform-aws-rds-cluster.git?ref=master"
  engine             = "aurora-mysql"
  cluster_family     = "aurora-mysql5.7"
  cluster_size       = "${var.rds_cluster_size}"
  namespace          = "dc"
  stage              = "${element(split("-", var.name), 1)}"
  name               = "${element(split("-", var.name), 0)}"
  admin_user         = "${element(split("-", var.name), 0)}"
  admin_password     = "${random_string.password.result}"
  db_name            = "${element(split("-", var.name), 0)}"
  instance_type      = "${var.rds_instance_type}"
  vpc_id             = "${aws_vpc.this.id}"
  availability_zones = ["${var.azs}"]
  security_groups    = ["${module.security_group_webapp.this_security_group_id}", "${module.security_group_bastion.this_security_group_id}"]
  subnets            = ["${aws_subnet.private.*.id}"]
  # zone_id            = "${aws_route53_zone.internal.zone_id}"
  storage_encrypted  = true
  maintenance_window = "wed:03:00-wed:04:00"
  skip_final_snapshot = false
}

I assume that it would work fine with the availability_zones variable dropped.

[nodomain]

See also hashicorp/terraform#16724 (comment)

[aknysh]

thanks @nodomain
we'll review it promptly

[thoellrich]

One more report on the very same issue as reported. And again it seems to be related to AZs in a different region this time. My config specifies 2a and 2b. us-east-2 has 3 AZs.

[aknysh]

thanks @nodomain and @thoellrich
addressed in #38

[thoellrich]

Thanks for the fix! This appears to be corrected now in my environment. Appreciate the quick response.