Add lint for db_instance engine

Author: chaspy

rules/aws_db_instance_invalid_engine.go

@@ -0,0 +1,80 @@
+package rules
+
+import (
+	"fmt"
+
+	hcl "github.com/hashicorp/hcl/v2"
+	"github.com/terraform-linters/tflint-plugin-sdk/tflint"
+	"github.com/terraform-linters/tflint-ruleset-aws/project"
+)
+
+// AwsDBInstanceInvalidEngineRule checks whether "aws_db_instance" has invalid engine.
+type AwsDBInstanceInvalidEngineRule struct {
+	resource      string
+	attributeName string
+	engines       map[string]bool
+}
+
+// NewAwsDBInstanceInvalidEngineRule returns new rule with default attributes
+func NewAwsDBInstanceInvalidEngineRule() *AwsDBInstanceInvalidEngineRule {
+	return &AwsDBInstanceInvalidEngineRule{
+		resource:      "aws_db_instance",
+		attributeName: "instance_class",
+		engines: map[string]bool{
+			// https://docs.aws.amazon.com/cli/latest/reference/rds/describe-db-engine-versions.html#options
+			"aurora":            true,
+			"aurora-mysql":      true,
+			"aurora-postgresql": true,
+			"mariadb":           true,
+			"mysql":             true,
+			"oracle-ee":         true,
+			"oracle-se2":        true,
+			"oracle-se1":        true,
+			"oracle-se":         true,
+			"postgres":          true,
+			"sqlserver-ee":      true,
+			"sqlserver-se":      true,
+			"sqlserver-ex":      true,
+			"sqlserver-web":     true,
+		},
+	}
+}
+
+// Name returns the rule name
+func (r *AwsDBInstanceInvalidEngineRule) Name() string {
+	return "aws_db_instance_invalid_type"
+}
+
+// Enabled returns whether the rule is enabled by default
+func (r *AwsDBInstanceInvalidEngineRule) Enabled() bool {
+	return true
+}
+
+// Severity returns the rule severity
+func (r *AwsDBInstanceInvalidEngineRule) Severity() string {
+	return tflint.ERROR
+}
+
+// Link returns the rule reference link
+func (r *AwsDBInstanceInvalidEngineRule) Link() string {
+	return project.ReferenceLink(r.Name())
+}
+
+// Check checks whether "aws_db_instance" has invalid engine.
+func (r *AwsDBInstanceInvalidEngineRule) Check(runner tflint.Runner) error {
+	return runner.WalkResourceAttributes(r.resource, r.attributeName, func(attribute *hcl.Attribute) error {
+		var engine string
+		err := runner.EvaluateExpr(attribute.Expr, &engine, nil)
+
+		return runner.EnsureNoError(err, func() error {
+			if !r.engines[engine] {
+				runner.EmitIssueOnExpr(
+					r,
+					fmt.Sprintf("\"%s\" is invalid engine.", engine),
+					attribute.Expr,
+				)
+			}
+			return nil
+		})
+	})
+}