Health checks failed with these codes: [502] - Cloudformation

Question

Hi I am using cloudforamtion to create ecs cluster, service and task. In task I am simply pulling wordpress image and connecting it to rds database. The problem here is the instance in the target group goes to draining state and then turn unhealthy. Wordpress shows up in the dns of alb but when you refresh it sometime gives error 502 bad gateway. I am only attaching the template where the error can exist most probably I might be giving the port wrong. I have good connection to the database (I have checked it as I did ssh into the instance and then used mysql -umysqldb -pmysql123a -h rds.endpoint command). The targets in targetgroup shoes an error Health checks failed with these codes: [502]

Task:

---
AWSTemplateFormatVersion: 2010-09-09 
Parameters:
    ExRole:
      Type: String
    RDS:
      Type: String
Resources:
    Task:
        Type: AWS::ECS::TaskDefinition
        Properties:
            Family: wordpress 
            Cpu: 1 vCPU
            ExecutionRoleArn: !Ref ExRole
            Memory: 1 GB
            NetworkMode: bridge
            RequiresCompatibilities:
                - EC2
            TaskRoleArn: !Ref ExRole
            ContainerDefinitions: 
              - Essential: true
                Image: wordpress:latest
                Name: wordpress
                PortMappings:  
                  - ContainerPort: 80
                    HostPort: 0
                    Protocol: tcp 
                Environment:
                  - Name: WORDPRESS_DB_HOST
                    Value: !Ref RDS 
                  - Name: WORDPRESS_DB_USER
                    Value: mysqldb 
                  - Name: WORDPRESS_DB_PASSWORD
                    Value: mysql123a 
                  - Name: WORDPRESS_DB_NAME
                    Value: mysqldb 
    
Outputs:
  Task:
    Description: Contains all the task specifications
    Value: !Ref Task
    Export:
      Name: "Task"

alb:

---
AWSTemplateFormatVersion: 2010-09-09
Parameters:
    SubnetA:
      Type: String
    SubnetB:
      Type: String
    VpcID:
      Type: String
Resources:
    Albsg:
        Type: AWS::EC2::SecurityGroup
        Properties:
            GroupName: alb-sg
            VpcId: !Ref VpcID
            SecurityGroupIngress:
                - IpProtocol: tcp
                  FromPort: 80
                  ToPort: 80
                  CidrIp: 0.0.0.0/0
                  Description: For traffic from Internet
            GroupDescription: Security Group for demo server
    Alb:
        Type: AWS::ElasticLoadBalancingV2::LoadBalancer
        Properties: 
            IpAddressType: ipv4
            Name: Alb
            Scheme: internet-facing
            SecurityGroups: 
                - !Ref Albsg
            Subnets:
                - Ref: "SubnetA"
                - Ref: "SubnetB"
            Type: application
    DefaultTargetGroup:
        Type: AWS::ElasticLoadBalancingV2::TargetGroup
        DependsOn: Alb
        Properties:
            Name: alb-tg
            VpcId: !Ref VpcID
            Port: 80
            Protocol: HTTP
    LoadBalancerListener:
        Type: AWS::ElasticLoadBalancingV2::Listener
        Properties:
            LoadBalancerArn: !Ref Alb
            Port: 80
            Protocol: HTTP
            DefaultActions:
                - Type: forward
                  TargetGroupArn: !Ref DefaultTargetGroup
Outputs:
  Albsg:
    Description: security group for application load balancer
    Value: !Ref Albsg
    Export:
        Name: "Albsg"
  Alb:
    Description: application load balancer
    Value: !Ref Alb
    Export:
      Name: "Alb"
  DefaultTargetGroup:
    Description: Default Target Group
    Value: !Ref DefaultTargetGroup
    Export:
      Name: "DefaultTargetGroup"
           

Cluster and service

---
AWSTemplateFormatVersion: 2010-09-09

Parameters:

  KeyName:
    Type: AWS::EC2::KeyPair::KeyName
    Default: webserver

  DesiredCapacity:
    Type: Number
    Default: 2

  MinSize:
    Type: Number
    Default: 1

  MaxSize:
    Type: Number
    Default: 4  

  InstanceProfile:
    Type: String

  DefaultTargetGroup:
    Type: String
  
  Task:
    Type: String

  Albsg:
    Type: String

  VpcID:
    Type: String

  SubnetA:
    Type: String
      
  SubnetB:
    Type: String
  
  webserver:
    Type: String


Resources:

  MyCluster:
      Type: AWS::ECS::Cluster
      Properties: {}

  Myservice:
      Type: AWS::ECS::Service
      Properties: 
          Cluster: !Ref MyCluster        
          DeploymentController:   
              Type: ECS
          DesiredCount: 2
          LaunchType: EC2
          LoadBalancers: 
              - ContainerName: wordpress
                ContainerPort: 80
                TargetGroupArn: !Ref DefaultTargetGroup
          #Role: !Ref InstanceProfile
          SchedulingStrategy: REPLICA
          ServiceName: wordpress
          TaskDefinition: !Ref Task

  ec2instance:
    Type: AWS::AutoScaling::LaunchConfiguration
    Properties:
      UserData:
        Fn::Base64: !Sub |
          #!/bin/bash -xe

          yum update -y && yum install -y aws-cfn-bootstrap 

          echo ECS_CLUSTER=${MyCluster} >> /etc/ecs/ecs.config
          echo ECS_BACKEND_HOST= >> /etc/ecs/ecs.config           

          /opt/aws/bin/cfn-signal -e $? \
                --stack ${AWS::StackName} \
                --resource myASG \
                --region ${AWS::Region}

      BlockDeviceMappings:
        - DeviceName: /dev/xvda
          Ebs:
            DeleteOnTermination: "true"
            VolumeSize: 30
            VolumeType: gp2
      ImageId: ami-06e05a843071324d1 
      InstanceType: t2.small
      IamInstanceProfile: !Ref InstanceProfile
      KeyName: !Ref KeyName
      SecurityGroups:
          - Ref: webserver

  myASG:
    Type: AWS::AutoScaling::AutoScalingGroup
    CreationPolicy:
      ResourceSignal:
        Timeout: PT5M
        Count: !Ref DesiredCapacity
    Properties:
      #AutoScalingGroupName: myASG
      MinSize: !Ref MinSize
      MaxSize: !Ref MaxSize
      DesiredCapacity: !Ref DesiredCapacity
      HealthCheckGracePeriod: 300
      LaunchConfigurationName:
        Ref: ec2instance
      VPCZoneIdentifier:
        - !Ref SubnetA
        - !Ref SubnetB
      TargetGroupARNs:
        - !Ref DefaultTargetGroup

Answer 1

most probably I might be giving the port wrong

In your Type: AWS::ECS::TaskDefinition you have defined port 80 for the wordpress.

But your target group is using port 8080:

       Properties:
            Name: alb-tg
            VpcId: !Ref VpcID
            Port: 8080 # <--- should be 80
            Protocol: HTTP

To use 302 code for health checks:

    DefaultTargetGroup:
        Type: AWS::ElasticLoadBalancingV2::TargetGroup
        DependsOn: Alb
        Properties:
            Name: alb-tg
            VpcId: !Ref VpcID
            Port: 80
            Protocol: HTTP
            Matcher: 
              HttpCode: 302