New Resource: aws_db_proxy_default_target_group (#12743)

Output from acceptance testing:

```
--- PASS: TestAccAWSDBProxyDefaultTargetGroup_Basic (737.81s)
--- PASS: TestAccAWSDBProxyDefaultTargetGroup_MaxIdleConnectionsPercent (740.15s)
--- PASS: TestAccAWSDBProxyDefaultTargetGroup_MaxConnectionsPercent (748.09s)
--- PASS: TestAccAWSDBProxyDefaultTargetGroup_SessionPinningFilters (756.04s)
--- PASS: TestAccAWSDBProxyDefaultTargetGroup_InitQuery (765.73s)
--- PASS: TestAccAWSDBProxyDefaultTargetGroup_ConnectionBorrowTimeout (780.68s)
--- PASS: TestAccAWSDBProxyDefaultTargetGroup_disappears (786.01s)
```

aws/provider.go

@@ -508,6 +508,7 @@ func Provider() *schema.Provider {
 			"aws_db_option_group":                                     resourceAwsDbOptionGroup(),
 			"aws_db_parameter_group":                                  resourceAwsDbParameterGroup(),
 			"aws_db_proxy":                                            resourceAwsDbProxy(),
+			"aws_db_proxy_default_target_group":                       resourceAwsDbProxyDefaultTargetGroup(),
 			"aws_db_security_group":                                   resourceAwsDbSecurityGroup(),
 			"aws_db_snapshot":                                         resourceAwsDbSnapshot(),
 			"aws_db_subnet_group":                                     resourceAwsDbSubnetGroup(),

aws/resource_aws_db_proxy_default_target_group.go

@@ -0,0 +1,234 @@
+package aws
+
+import (
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/service/rds"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/resource"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/validation"
+)
+
+func resourceAwsDbProxyDefaultTargetGroup() *schema.Resource {
+	return &schema.Resource{
+		Create: resourceAwsDbProxyDefaultTargetGroupCreate,
+		Read:   resourceAwsDbProxyDefaultTargetGroupRead,
+		Update: resourceAwsDbProxyDefaultTargetGroupUpdate,
+		Delete: schema.Noop,
+		Importer: &schema.ResourceImporter{
+			State: schema.ImportStatePassthrough,
+		},
+
+		Timeouts: &schema.ResourceTimeout{
+			Create: schema.DefaultTimeout(30 * time.Minute),
+			Update: schema.DefaultTimeout(30 * time.Minute),
+		},
+
+		Schema: map[string]*schema.Schema{
+			"arn": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"db_proxy_name": {
+				Type:         schema.TypeString,
+				Required:     true,
+				ForceNew:     true,
+				ValidateFunc: validateRdsIdentifier,
+			},
+			"name": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+			"connection_pool_config": {
+				Type:     schema.TypeList,
+				Required: true,
+				MaxItems: 1,
+				Elem: &schema.Resource{
+					Schema: map[string]*schema.Schema{
+						"connection_borrow_timeout": {
+							Type:         schema.TypeInt,
+							Optional:     true,
+							Default:      120,
+							ValidateFunc: validation.IntBetween(0, 3600),
+						},
+						"init_query": {
+							Type:     schema.TypeString,
+							Optional: true,
+						},
+						"max_connections_percent": {
+							Type:         schema.TypeInt,
+							Optional:     true,
+							Default:      100,
+							ValidateFunc: validation.IntBetween(1, 100),
+						},
+						"max_idle_connections_percent": {
+							Type:         schema.TypeInt,
+							Optional:     true,
+							Default:      50,
+							ValidateFunc: validation.IntBetween(0, 100),
+						},
+						"session_pinning_filters": {
+							Type:     schema.TypeSet,
+							Optional: true,
+							Elem: &schema.Schema{
+								Type: schema.TypeString,
+								// This isn't available as a constant
+								ValidateFunc: validation.StringInSlice([]string{
+									"EXCLUDE_VARIABLE_SETS",
+								}, false),
+							},
+							Set: schema.HashString,
+						},
+					},
+				},
+			},
+		},
+	}
+}
+
+func resourceAwsDbProxyDefaultTargetGroupRead(d *schema.ResourceData, meta interface{}) error {
+	conn := meta.(*AWSClient).rdsconn
+
+	tg, err := resourceAwsDbProxyDefaultTargetGroupGet(conn, d.Id())
+
+	if err != nil {
+		if isAWSErr(err, rds.ErrCodeDBProxyNotFoundFault, "") {
+			log.Printf("[WARN] DB Proxy (%s) not found, removing from state", d.Id())
+			d.SetId("")
+			return nil
+		}
+		return fmt.Errorf("error reading RDS DB Proxy (%s) Default Target Group: %w", d.Id(), err)
+	}
+
+	if tg == nil {
+		log.Printf("[WARN] DB Proxy default target group (%s) not found, removing from state", d.Id())
+		d.SetId("")
+		return nil
+	}
+
+	d.Set("arn", tg.TargetGroupArn)
+	d.Set("db_proxy_name", tg.DBProxyName)
+	d.Set("name", tg.TargetGroupName)
+
+	cpc := tg.ConnectionPoolConfig
+	d.Set("connection_pool_config", flattenDbProxyTargetGroupConnectionPoolConfig(cpc))
+
+	return nil
+}
+
+func resourceAwsDbProxyDefaultTargetGroupCreate(d *schema.ResourceData, meta interface{}) error {
+	d.SetId(d.Get("db_proxy_name").(string))
+	return resourceAwsDbProxyDefaultTargetGroupCreateUpdate(d, meta, schema.TimeoutCreate)
+}
+
+func resourceAwsDbProxyDefaultTargetGroupUpdate(d *schema.ResourceData, meta interface{}) error {
+	return resourceAwsDbProxyDefaultTargetGroupCreateUpdate(d, meta, schema.TimeoutUpdate)
+}
+
+func resourceAwsDbProxyDefaultTargetGroupCreateUpdate(d *schema.ResourceData, meta interface{}, timeout string) error {
+	conn := meta.(*AWSClient).rdsconn
+
+	params := rds.ModifyDBProxyTargetGroupInput{
+		DBProxyName:     aws.String(d.Get("db_proxy_name").(string)),
+		TargetGroupName: aws.String("default"),
+	}
+
+	if v, ok := d.GetOk("connection_pool_config"); ok {
+		params.ConnectionPoolConfig = expandDbProxyConnectionPoolConfig(v.([]interface{}))
+	}
+
+	log.Printf("[DEBUG] Update DB Proxy default target group: %#v", params)
+	_, err := conn.ModifyDBProxyTargetGroup(&params)
+	if err != nil {
+		return fmt.Errorf("error updating RDS DB Proxy (%s) default target group: %w", d.Id(), err)
+	}
+
+	stateChangeConf := &resource.StateChangeConf{
+		Pending: []string{rds.DBProxyStatusModifying},
+		Target:  []string{rds.DBProxyStatusAvailable},
+		Refresh: resourceAwsDbProxyDefaultTargetGroupRefreshFunc(conn, d.Id()),
+		Timeout: d.Timeout(timeout),
+	}
+
+	_, err = stateChangeConf.WaitForState()
+	if err != nil {
+		return fmt.Errorf("Error waiting for DB Proxy default target group update: %s", err)
+	}
+
+	return resourceAwsDbProxyDefaultTargetGroupRead(d, meta)
+}
+
+func expandDbProxyConnectionPoolConfig(configs []interface{}) *rds.ConnectionPoolConfiguration {
+	if len(configs) < 1 {
+		return nil
+	}
+
+	config := configs[0].(map[string]interface{})
+
+	result := &rds.ConnectionPoolConfiguration{
+		ConnectionBorrowTimeout:   aws.Int64(int64(config["connection_borrow_timeout"].(int))),
+		InitQuery:                 aws.String(config["init_query"].(string)),
+		MaxConnectionsPercent:     aws.Int64(int64(config["max_connections_percent"].(int))),
+		MaxIdleConnectionsPercent: aws.Int64(int64(config["max_idle_connections_percent"].(int))),
+		SessionPinningFilters:     expandStringSet(config["session_pinning_filters"].(*schema.Set)),
+	}
+
+	return result
+}
+
+func flattenDbProxyTargetGroupConnectionPoolConfig(cpc *rds.ConnectionPoolConfigurationInfo) []interface{} {
+	if cpc == nil {
+		return []interface{}{}
+	}
+
+	m := make(map[string]interface{})
+	m["connection_borrow_timeout"] = aws.Int64Value(cpc.ConnectionBorrowTimeout)
+	m["init_query"] = aws.StringValue(cpc.InitQuery)
+	m["max_connections_percent"] = aws.Int64Value(cpc.MaxConnectionsPercent)
+	m["max_idle_connections_percent"] = aws.Int64Value(cpc.MaxIdleConnectionsPercent)
+	m["session_pinning_filters"] = flattenStringSet(cpc.SessionPinningFilters)
+
+	return []interface{}{m}
+}
+
+func resourceAwsDbProxyDefaultTargetGroupGet(conn *rds.RDS, proxyName string) (*rds.DBProxyTargetGroup, error) {
+	params := &rds.DescribeDBProxyTargetGroupsInput{
+		DBProxyName: aws.String(proxyName),
+	}
+
+	var defaultTargetGroup *rds.DBProxyTargetGroup
+	err := conn.DescribeDBProxyTargetGroupsPages(params, func(page *rds.DescribeDBProxyTargetGroupsOutput, lastPage bool) bool {
+		for _, targetGroup := range page.TargetGroups {
+			if *targetGroup.IsDefault {
+				defaultTargetGroup = targetGroup
+				return false
+			}
+		}
+		return !lastPage
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	// Return default target group
+	return defaultTargetGroup, nil
+}
+
+func resourceAwsDbProxyDefaultTargetGroupRefreshFunc(conn *rds.RDS, proxyName string) resource.StateRefreshFunc {
+	return func() (interface{}, string, error) {
+		tg, err := resourceAwsDbProxyDefaultTargetGroupGet(conn, proxyName)
+
+		if err != nil {
+			if isAWSErr(err, rds.ErrCodeDBProxyNotFoundFault, "") {
+				return 42, "", nil
+			}
+			return 42, "", err
+		}
+
+		return tg, *tg.Status, nil
+	}
+}