Want to use ECS service discovery with CloudFormation? Our Support Techs are here with an easy solution. Read on to find out more about it.

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About using ECS service discovery with CloudFormation

Although the Amazon ECS console permits you to create service discovery resources in the course of service creation, the AWS::ECS::Service resource type for CloudFormation doesn’t permit the same. If you want to use Amazon ECS service discovery with AWS CloudFormation, you have come to the right place.

How to use ECS service discovery with CloudFormation

1. First, go to the Resource section in the CloudFormation template and create a private service discovery namespace like example.com. Make sure you create the namespace in an existing Amazon VPC.
   For instance in JSON:

   { 
   "PrivateNamespace": { 
    "Type": "AWS::ServiceDiscovery::PrivateDnsNamespace", 
   "Properties": {
        "Name": "example.com", 
        "Vpc": "vpc-xxxxxxx" 
         }
      }
   }

   For instance, in YAML:

   PrivateNamespace: 
   Type: AWS::ServiceDiscovery::PrivateDnsNamespace 
   Properties: 
      Name: example.com 
      Vpc: vpc-xxxxxxx

   Remember to replace example.com with the namespace’s name and vpc-xxxxxxx with the ID of a VPC in your account.
2. Next, create a new service discovery service with the namespace ID created in the previous step.
   If you do not have namespace ID, you can use the Ref Intrinsic function in the CloudFormation to get it.
   For instance, in JSON:

   {
     "DiscoveryService": {
       "Type": "AWS::ServiceDiscovery::Service",
       "Properties": {
         "Description": "Discovery Service for the Demo Application",
         "DnsConfig": {
           "RoutingPolicy": "MULTIVALUE",
           "DnsRecords": [
             {
               "TTL": 60,
               "Type": "A"
             },
             {
               "TTL": 60,
               "Type": "SRV"
             }
           ]
         },
         "HealthCheckCustomConfig": {
           "FailureThreshold": 1
         },
         "Name": "example-service-name",
         "NamespaceId": {
           "Ref": "PrivateNamespace"
         }
       }
     }
   }

   For instance, in YAML:

   DiscoveryService:
     Type: AWS::ServiceDiscovery::Service
     Properties: 
       Description: Discovery Service for the Demo Application
       DnsConfig:
         RoutingPolicy: MULTIVALUE
         DnsRecords:
           - TTL: 60
             Type: A
           - TTL: 60
             Type: SRV
       HealthCheckCustomConfig: 
         FailureThreshold: 1
       Name: example-service-name
       NamespaceId: !Ref PrivateNamespace

   Remember to replace example-service-name with the service’s name. The DnsConfig property specifies DNS records created when the Amazon ECS task is registered with the service discovery service.

   Our Support Engineers recommend using the HealthCheckCustomConfig property. It allows Amazon ECS to pass on task health information to service discovery. In fact, Amazon ECS utilizes information from container checks, task state, and health checks to update service discovery’s health with AWS Cloud Map.

Integrating Amazon ECS service with a service discovery namespace

1. After that, we will create an Amazon ECS service that is integrated with the service created in the earlier steps and the service discovery namespace. We will utilize the ServiceRegisteries property in the AWS:ECS::Service for the integration.

   For instance, in JSON:

   {
     "EcsService": {
       "Type": "AWS::ECS::Service",
       "Properties": {
         "Cluster": "awsExampleCluster",
         "DesiredCount": 4,
         "LaunchType": "FARGATE",
         "NetworkConfiguration": {
           "AwsvpcConfiguration": {
             "SecurityGroups": [
               "sg-xxxxxxx"
             ],
             "Subnets": [
               "subnet-xxxxxxx"
             ]
           }
         },
         "ServiceName": "awsExampleService",
         "TaskDefinition": "awsExampleTaskDefinition",
         "ServiceRegistries": [
           {
             "RegistryArn": {
               "Fn::GetAtt": [
                 "DiscoveryService",
                 "Arn"
               ]
             },
             "Port": 80
           }
         ]
       }
     }
   }

   For instance, in YAML:

   EcsService:
     Type: AWS::ECS::Service
     Properties:
       Cluster: awsExampleCluster
       DesiredCount: 4
       LaunchType: FARGATE
       NetworkConfiguration:
         AwsvpcConfiguration:
           SecurityGroups:
             - sg-xxxxxxx
           Subnets:
             - subnet-xxxxxxx
       ServiceName: awsExampleService
       TaskDefinition: awsExampleTaskDefinition
       ServiceRegistries:
         - RegistryArn: !GetAtt DiscoveryService.Arn
           Port: 80

   Here, we will replace awsExampleCluster, awsExampleService. awsExampleService and subnet-xxxxxxx with the cluster, service, task definition, and security group ID respectively.

   We will also have to set the RegistryArn property to the ARN of the service discovery service’s value for the integration. We can get this value from the CloudFormation with the Fn::GetAtt Intrinsic function.

   In case you are using awsvpc mode, set the value to either a combination of ContainerName and ContainerPort or Port. However, if you are using host or bridge, set it to ContainerName or ContainerPort.
2. The next step is to run the following commands to verify that the tasks can be resolved from the VPC:

   $ dig awsExampleService.awsExampleNamespace. +short
   $ dig srv awsExampleService.awsExampleNamespace. +short
   $ curl awsExampleService.awsExampleNamespace. -I

   Here, awsExampleService and awsExampleNamespace is the name of the AWS::ECS::Service resource and AWS::ServiceDiscovery::PrivateDnsNamespace resource respectively.

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   Conclusion

   To sum up, we learned how to use ECS service discovery with CloudFormation from the skilled Support Engineers at Bobcares.

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