Cannot connect two ECS services via Service Discovery

user_11371473 0
Viewed 1068

I am new to AWS and I am trying to deploy simple app to AWS ECS. I have two simple docker containers, running in ECS Fargate:

  • ‘Frontend’: Vue Js app, which makes a single request to backend;
  • ‘Backend’: Django app, which serves the request;

Both services were launched within the same cluster, in default VPC and the same, single public subnet. For ‘Backend’ I configured Service Discovery: Namespace – test, Service Discovery Name – backend. Security group configured to allow All Traffic.

So, the problem is when frontend makes request: 

axios.get('http://backend.test:8000/api/get-test/')

I got error: Failed to load resource: net::ERR_NAME_NOT_RESOLVED backend.test:8000/api/get-test/

However, executing in AWS Cloud9 command: dig +short backend.test returns correct private IP of the backend container.

When I change request to something like 

axios.get('http://172.17.3.85:8000/api/get-test/')

where 172.17.3.85 is valid private IP of the backend container, I got following error:

GET http://172.17.3.85:8000/api/get-test/ net::ERR_CONNECTION_TIMED_OUT

However, if I spin out EC2 instance in the same VPC and subnet and SSH to it, I can ping backend container, and requests - 

curl -v http://172.17.3.85:8000/api/get-test/

as well as 

curl -v http://backend.test:8000/api/get-test/

return desired response.

The only case when everything is working as expected is when the request is like

axios.get('http://3.18.59.133:8000/api/get-test/'),

where 3.18.59.133 is valid Public IP of the backend container.

I would appreciate any suggestion where look further or how to connect two containers via service discovery as right now I am out of ideas.

amazon-ecs amazon-web-services
1 Answers

Based on the discussion in comments and description of the problem, the reason is that the Frontend’: Vue Js app executes on the client side, for example, in the browser.

This explains all the issues described and discussed:

  • axios.get('http://backend.test:8000/api/get-test/') does not work as on the client side you can't resolve privte hosted zone.

  • axios.get('http://172.17.3.85:8000/api/get-test/') does not work because the 172.17.3.85 is valid only in the VPC, not on the client's network.

  • spin out EC2 instance in the same VPC and subnet and SSH works because private hosted zones can be resolved inside VPC.

  • axios.get('http://3.18.59.133:8000/api/get-test/') works because public IP can be used on the clinet side, unlike private IPs.

user_2488230
Related