Add in provider options for DB Connection Pools (#3)

* Add in provider options for DB Connection Pools

The defaults maintain the current configuration, but this allows users to tune db connections for individual needs.

In particular, even with the latest go libraries, we often encounter "cannot allocate memory" errors when creating yet another DB connection. We have a large number of resources across multiple DBs, so this happens frequently. For our uses, enabling connection pooling is going to save us a lot of headaches and the edge case disabling the connection pooling is guarding against unlikely to be an issue.

* Use `any` and add some documentation for connection timing

Author: aarontatar-upguard

postgresql/config.go

@@ -8,6 +8,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"time"
 	"unicode"
 
 	"github.com/blang/semver"
@@ -179,6 +180,9 @@ type Config struct {
 	Timeout                         int
 	ConnectTimeoutSec               int
 	MaxConns                        int
+	MaxIdleConns                    int
+	ConnMaxIdleTime                 time.Duration
+	ConnMaxLifetime                 time.Duration
 	ExpectedVersion                 semver.Version
 	SSLClientCert                   *ClientCertificateConfig
 	SSLRootCertPath                 string
@@ -308,8 +312,10 @@ func (c *Client) Connect() (*DBConnection, error) {
 		// We don't want to retain connection
 		// So when we connect on a specific database which might be managed by terraform,
 		// we don't keep opened connection in case of the db has to be dropped in the plan.
-		db.SetMaxIdleConns(0)
+		db.SetMaxIdleConns(c.config.MaxIdleConns)
 		db.SetMaxOpenConns(c.config.MaxConns)
+		db.SetConnMaxIdleTime(c.config.ConnMaxIdleTime)
+		db.SetConnMaxIdleTime(c.config.ConnMaxLifetime)
 
 		defaultVersion, _ := semver.Parse(defaultExpectedPostgreSQLVersion)
 		version := &c.config.ExpectedVersion

postgresql/provider.go

@@ -3,9 +3,11 @@ package postgresql
 import (
 	"context"
 	"fmt"
+	"os"
+	"time"
+
 	"github.com/aws/aws-sdk-go-v2/credentials"
 	"github.com/aws/aws-sdk-go-v2/service/sts"
-	"os"
 
 	"github.com/Azure/azure-sdk-for-go/sdk/azcore/policy"
 	"github.com/Azure/azure-sdk-for-go/sdk/azidentity"
@@ -21,8 +23,12 @@ import (
 )
 
 const (
-	defaultProviderMaxOpenConnections = 20
-	defaultExpectedPostgreSQLVersion  = "9.0.0"
+	defaultProviderMaxOpenConnections = 20 // sql.DB Default
+	defaultProviderMaxIdleConnections = 0
+	// Keep connection lifetimes short by default, to prevent blocking 'destroy' actions on database instance resources.
+	defaultProviderConnectionMaxIdleTime = time.Second * 5
+	defaultProviderConnectionMaxLifetime = time.Second * 10
+	defaultExpectedPostgreSQLVersion     = "9.0.0"
 )
 
 // Provider returns a terraform.ResourceProvider.
@@ -192,6 +198,35 @@ func Provider() *schema.Provider {
 				Description:  "Maximum number of connections to establish to the database. Zero means unlimited.",
 				ValidateFunc: validation.IntAtLeast(-1),
 			},
+			"max_idle_connections": {
+				Type:     schema.TypeInt,
+				Optional: true,
+				Default:  defaultProviderMaxIdleConnections,
+				Description: "Maximum number of idle connections to hold for the database. " +
+					"NOTE: Idle connections that aren't cleaned-up can cause problems if a database is destroyed in " +
+					"the same plan. The default is 0 to prevent that issue.",
+				ValidateFunc: validation.IntAtLeast(-1),
+			},
+			"connection_max_idle_time": {
+				Type:     schema.TypeString,
+				Optional: true,
+				Default:  defaultProviderConnectionMaxIdleTime.String(),
+				Description: "Duration to hold idle connections to the database. Setting to 0 will hold connections " + "" +
+					"forever. " +
+					"NOTE: Idle connections that aren't cleaned-up can cause problems if a database is destroyed in " +
+					"the same plan. This should be > 0 to prevent that.",
+				ValidateFunc: validateParsableDuration,
+			},
+			"connection_max_lifetime": {
+				Type:     schema.TypeString,
+				Optional: true,
+				Default:  defaultProviderConnectionMaxLifetime.String(),
+				Description: "Maximum lifetime of any connections to the database. Setting to 0 will hold " +
+					"connections forever. " +
+					"NOTE: Idle connections that aren't cleaned-up can cause problems if a database is destroyed in " +
+					"the same plan. This should be > 0 to prevent that.",
+				ValidateFunc: validateParsableDuration,
+			},
 			"expected_version": {
 				Type:         schema.TypeString,
 				Optional:     true,
@@ -236,6 +271,13 @@ func validateExpectedVersion(v interface{}, key string) (warnings []string, erro
 	return
 }
 
+func validateParsableDuration(v any, _ string) (warnings []string, errors []error) {
+	if _, err := time.ParseDuration(v.(string)); err != nil {
+		errors = append(errors, fmt.Errorf("invalid duration (%q): %w", v.(string), err))
+	}
+	return
+}
+
 func getRDSAuthToken(region string, profile string, role string, username string, host string, port int) (string, error) {
 	endpoint := fmt.Sprintf("%s:%d", host, port)
 
@@ -367,6 +409,10 @@ func providerConfigure(d *schema.ResourceData) (interface{}, error) {
 		password = d.Get("password").(string)
 	}
 
+	// Safe to ignore the error, since this is already checked in validation
+	connMaxIdleTime, _ := time.ParseDuration(d.Get("connection_max_idle_time").(string))
+	connMaxLifetime, _ := time.ParseDuration(d.Get("connection_max_lifetime").(string))
+
 	config := Config{
 		Scheme:                          d.Get("scheme").(string),
 		Host:                            host,
@@ -379,6 +425,9 @@ func providerConfigure(d *schema.ResourceData) (interface{}, error) {
 		ApplicationName:                 "Terraform provider",
 		ConnectTimeoutSec:               d.Get("connect_timeout").(int),
 		MaxConns:                        d.Get("max_connections").(int),
+		MaxIdleConns:                    d.Get("max_idle_connections").(int),
+		ConnMaxIdleTime:                 connMaxIdleTime,
+		ConnMaxLifetime:                 connMaxLifetime,
 		ExpectedVersion:                 version,
 		SSLRootCertPath:                 d.Get("sslrootcert").(string),
 		GCPIAMImpersonateServiceAccount: d.Get("gcp_iam_impersonate_service_account").(string),