HttpRequestException when making http request between Localstack Lambda and docker container

Question

I've got two docker containers running as part of a docker-compose file, ContainerA is localstack where I'm running a lambda function which is trying to make a HTTP POST request to ContainerB using the below simplified code:

var content = new StringContent("{ "content": "sample" }", Encoding.UTF8, "application/json");
var httpClient = new HttpClient();
var response = await HttpClient.PostAsync("http://ContainerB/Foo", content);

Which raises the following exception:

Request failed - System.Net.Http.HttpRequestException: Name or service not known

If I make the same request from the console of Container A this request succeeds e.g.

curl http://ContainerB/Foo -H "Content-Type: application/json" -d "{ "content": "sample" }"

As this request succeeds from the console I'm fairly confident that it's not a networking issue between my docker containers.

Adam T · Accepted Answer · 2020-11-02 16:48:45Z

0

Localstack lambda's are created in a new Docker container per execution, this continer is outside of the docker-compose stack and therefore it is not a part of the docker-compose default network. See this GitHub issue for more information.

In order to work around this, you must first create an external bridge network within docker:

docker network create -d bridge MyNetwork

And then connect each docker container to it within your docker compose file and register this as an external network:

services:
  localstack:
    networks:
      - MyNetwork
  ...
  ...

networks:
  MyNetwork:
    external: true

answered Nov 2, 2020 at 16:48

Adam T

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