How to get RDS instance hostname in CDK app?

Question

I'm using the AWS CDK for .NET to create a stack that consists of a VPC, an RDS Database Instance and an Application Load Balanced Fargate Service in ECS. The container I'm deploying to ECS requires connection information for the RDS database to be set via environment variables, but I'm not sure how to access that information. Below is my CDK code.

using Amazon.CDK;
using EC2 = Amazon.CDK.AWS.EC2;
using ECS = Amazon.CDK.AWS.ECS;
using RDS = Amazon.CDK.AWS.RDS;

namespace PersonalSecOps
{
    public class PersonalSecOpsStack : Stack
    {
        internal PersonalSecOpsStack(Construct scope, string id, IStackProps props = null) : base(scope, id, props)
        {
            var vpc = new EC2.Vpc(this, "PersonalSecOpsVpc", new EC2.VpcProps
            {
                MaxAzs = 3 // Default is all AZs in region
            });

            var mySql = new RDS.DatabaseInstance(this, "PersonalSecOpsRds", new RDS.DatabaseInstanceProps
            {
                Engine = RDS.DatabaseInstanceEngine.MYSQL,
                PreferredBackupWindow = "05:00-06:00",
                BackupRetention = Duration.Days(7),
                RemovalPolicy = RemovalPolicy.DESTROY,
                DeletionProtection = false,
                MasterUsername = "admin",
                InstanceClass = EC2.InstanceType.Of(EC2.InstanceClass.BURSTABLE2, EC2.InstanceSize.MICRO),
                Vpc = vpc,
                InstanceIdentifier = "PersonalSecOpsRds"
            });

            var ecsCluster = new ECS.Cluster(this, "PersonalSecOpsEcs", new ECS.ClusterProps
            {
                Vpc = vpc
            });

            var nextCloudService = new ECS.Patterns.ApplicationLoadBalancedFargateService(this, "NextcloudService", new ECS.Patterns.ApplicationLoadBalancedFargateServiceProps
            {
                Cluster = ecsCluster,
                DesiredCount = 1,
                TaskImageOptions = new ECS.Patterns.ApplicationLoadBalancedTaskImageOptions
                {
                    Image = ECS.ContainerImage.FromRegistry("nextcloud"),
                    Secrets = 
                    {
                        { "MYSQL_PASSWORD", ??? }
                    },
                    Environment = {
                        { "MYSQL_DATABASE", "Nextcloud" },
                        { "MYSQL_USER", "admin" },
                        { "MYSQL_HOST", ??? }
                    } 
                },
                MemoryLimitMiB = 2048,
                PublicLoadBalancer = true
            });
        }
    }
}

Notice the two "???" where I'm attempting to set the MYSQL_PASSWORD and MYSQL_HOST environment variables on the container. I read somewhere that RDS will automatically generate a MasterUserPassword and store it in Secret Manager, but I'm not sure how to get that out. Also, I need the hostname of the RDS instance. I haven't been able to find a way to set it explicitly when creating the instance or I would just do that.

Am I going about this the right way?

Answer 1

Thanks to kingofpoptart on Reddit for helping to answer this question.

using Amazon.CDK;
using EC2 = Amazon.CDK.AWS.EC2;
using ECS = Amazon.CDK.AWS.ECS;
using RDS = Amazon.CDK.AWS.RDS;

namespace PersonalSecOps
{
    public class PersonalSecOpsStack : Stack
    {
        internal PersonalSecOpsStack(Construct scope, string id, IStackProps props = null) : base(scope, id, props)
        {
            var vpc = new EC2.Vpc(this, "PersonalSecOpsVpc", new EC2.VpcProps
            {
                MaxAzs = 3 // Default is all AZs in region
            });

            var mySqlPassword = new Secret(this, "PersonalSecOpsMySqlPassword", new SecretProps
            {
                GenerateSecretString = new SecretStringGenerator
                {
                    PasswordLength = 20
                }
            });

            var mySql = new RDS.DatabaseInstance(this, "PersonalSecOpsRds", new RDS.DatabaseInstanceProps
            {
                Engine = RDS.DatabaseInstanceEngine.MYSQL,
                PreferredBackupWindow = "05:00-06:00",
                BackupRetention = Duration.Days(7),
                RemovalPolicy = RemovalPolicy.DESTROY,
                DeletionProtection = false,
                MasterUsername = "admin",
                MasterUserPassword = mySqlPassword.SecretValue,
                InstanceClass = EC2.InstanceType.Of(EC2.InstanceClass.BURSTABLE2, EC2.InstanceSize.MICRO),
                Vpc = vpc,
                InstanceIdentifier = "PersonalSecOpsRds"
            });

            var ecsCluster = new ECS.Cluster(this, "PersonalSecOpsEcs", new ECS.ClusterProps
            {
                Vpc = vpc
            });

            var nextCloudService = new ECS.Patterns.ApplicationLoadBalancedFargateService(this, "NextcloudService", new ECS.Patterns.ApplicationLoadBalancedFargateServiceProps
            {
                Cluster = ecsCluster,
                DesiredCount = 1,
                TaskImageOptions = new ECS.Patterns.ApplicationLoadBalancedTaskImageOptions
                {
                    Image = ECS.ContainerImage.FromRegistry("nextcloud"),
                    Secrets = 
                    {
                        { "MYSQL_PASSWORD", ECS.Secret.FromSecretsManager(mySqlPassword) }
                    },
                    Environment = {
                        { "MYSQL_DATABASE", "Nextcloud" },
                        { "MYSQL_USER", "admin" },
                        { "MYSQL_HOST", mySql.DbInstanceEndpointAddress }
                    } 
                },
                MemoryLimitMiB = 2048,
                PublicLoadBalancer = true
            });
        }
    }
}