fargate failing on docker pull in private subnet - aws-cloudformation

Question

I am having trouble deploying a fargate cluster, and it is failing on the docker pull image with error "CannotPullContainerError". I am creating the stack with cloudformation, which is not optional, and it creates the full stack, but fails when trying to start the task based on the above error.
I have attached the cloudformation stack file which might highlight the problem, and I have doubled checked that the subnet has a route to nat(below). I also ssh'ed into an instance in the same subnet which was able to route externally. I am wondering if i have not correctly placed the pieces required i.e the service + loadbalancer are in the private subnet, or should i not be placing the internal lb in the same subnet???
This subnet is the one that currently has the placement but all 3 in the file have the same nat settings.
subnet routable (subnet-34b92250)
* 0.0.0.0/0 -> nat-05a00385366da527a
cheers in advance.
yaml cloudformaition script:
AWSTemplateFormatVersion: 2010-09-09
Description: Cloudformation stack for the new GRPC endpoints within existing vpc/subnets and using fargate
Parameters:
StackName:
Type: String
Default: cf-core-ci-grpc
Description: The name of the parent Fargate networking stack that you created. Necessary
vpcId:
Type: String
Default: vpc-0d499a68
Description: The name of the parent Fargate networking stack that you created. Necessary
Resources:
CoreGrcpInstanceSecurityGroupOpenWeb:
Type: 'AWS::EC2::SecurityGroup'
Properties:
GroupName: sgg-core-ci-grpc-ingress
GroupDescription: Allow http to client host
VpcId: !Ref vpcId
SecurityGroupIngress:
- IpProtocol: tcp
FromPort: '80'
ToPort: '80'
CidrIp: 0.0.0.0/0
SecurityGroupEgress:
- IpProtocol: tcp
FromPort: '80'
ToPort: '80'
CidrIp: 0.0.0.0/0
LoadBalancer:
Type: 'AWS::ElasticLoadBalancingV2::LoadBalancer'
DependsOn:
- CoreGrcpInstanceSecurityGroupOpenWeb
Properties:
Name: lb-core-ci-int-grpc
Scheme: internal
Subnets:
# # pub
# - subnet-f13995a8
# - subnet-f13995a8
# - subnet-f13995a8
# pri
- subnet-34b92250
- subnet-82d85af4
- subnet-ca379b93
LoadBalancerAttributes:
- Key: idle_timeout.timeout_seconds
Value: '50'
SecurityGroups:
- !Ref CoreGrcpInstanceSecurityGroupOpenWeb
TargetGroup:
Type: 'AWS::ElasticLoadBalancingV2::TargetGroup'
DependsOn:
- LoadBalancer
Properties:
Name: tg-core-ci-grpc
Port: 3000
TargetType: ip
Protocol: HTTP
HealthCheckIntervalSeconds: 30
HealthCheckProtocol: HTTP
HealthCheckTimeoutSeconds: 10
HealthyThresholdCount: 4
Matcher:
HttpCode: '200'
TargetGroupAttributes:
- Key: deregistration_delay.timeout_seconds
Value: '20'
UnhealthyThresholdCount: 3
VpcId: !Ref vpcId
LoadBalancerListener:
Type: 'AWS::ElasticLoadBalancingV2::Listener'
DependsOn:
- TargetGroup
Properties:
DefaultActions:
- Type: forward
TargetGroupArn: !Ref TargetGroup
LoadBalancerArn: !Ref LoadBalancer
Port: 80
Protocol: HTTP
EcsCluster:
Type: 'AWS::ECS::Cluster'
DependsOn:
- LoadBalancerListener
Properties:
ClusterName: ecs-core-ci-grpc
EcsTaskRole:
Type: 'AWS::IAM::Role'
Properties:
AssumeRolePolicyDocument:
Statement:
- Effect: Allow
Principal:
Service:
# - ecs.amazonaws.com
- ecs-tasks.amazonaws.com
Action:
- 'sts:AssumeRole'
Path: /
Policies:
- PolicyName: iam-policy-ecs-task-core-ci-grpc
PolicyDocument:
Statement:
- Effect: Allow
Action:
- 'ecr:**'
Resource: '*'
CoreGrcpTaskDefinition:
Type: 'AWS::ECS::TaskDefinition'
DependsOn:
- EcsCluster
- EcsTaskRole
Properties:
NetworkMode: awsvpc
RequiresCompatibilities:
- FARGATE
ExecutionRoleArn: !Ref EcsTaskRole
Cpu: '1024'
Memory: '2048'
ContainerDefinitions:
- Name: container-core-ci-grpc
Image: 'nginx:latest'
Cpu: '256'
Memory: '1024'
PortMappings:
- ContainerPort: '80'
HostPort: '80'
Essential: 'true'
EcsService:
Type: 'AWS::ECS::Service'
DependsOn:
- CoreGrcpTaskDefinition
Properties:
Cluster: !Ref EcsCluster
LaunchType: FARGATE
DesiredCount: '1'
DeploymentConfiguration:
MaximumPercent: 150
MinimumHealthyPercent: 0
LoadBalancers:
- ContainerName: container-core-ci-grpc
ContainerPort: '80'
TargetGroupArn: !Ref TargetGroup
NetworkConfiguration:
AwsvpcConfiguration:
AssignPublicIp: DISABLED
SecurityGroups:
- !Ref CoreGrcpInstanceSecurityGroupOpenWeb
Subnets:
- subnet-34b92250
- subnet-82d85af4
- subnet-ca379b93
TaskDefinition: !Ref CoreGrcpTaskDefinition

Answer 1

Unfortunately AWS Fargate only supports images hosted in ECR or public repositories in Docker Hub and does not support private repositories which are hosted in Docker Hub. For more info - https://forums.aws.amazon.com/thread.jspa?threadID=268415
Even we faced the same problem using AWS Fargate couple of months back. You have only two options right now:
Migrate your images to Amazon ECR.
Use AWS Batch with custom AMI, where the custom AMI is built with Docker Hub credentials in ECS config (which we are using right now).
Edit: As mentioned by Christopher Thomas in the comment, ECS fargate now supports pulling images from DockerHub Private repositories. More info on how to set it up can be found here.

Answer 2

Do define this policy in your ECR registry and attach the IAM role with your task.
{
"Version": "2008-10-17",
"Statement": [
{
"Sid": "new statement",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::99999999999:role/ecsEventsRole"
},
"Action": [
"ecr:GetDownloadUrlForLayer",
"ecr:BatchGetImage",
"ecr:BatchCheckLayerAvailability",
"ecr:PutImage",
"ecr:InitiateLayerUpload",
"ecr:UploadLayerPart",
"ecr:CompleteLayerUpload"
]
}
]
}