Connection Refused when connecting two containers in docker-compose - asp.net

Question

I'm new to docker and I'm facing a problem when trying to connect to a container from within another. The wierd stuff is that some containers can indeed be contacted, and others, configured in the same way, not. I tried a zillion fixes found while crawling google, nothing works. I guess this is a simple noob mistake though.
Here's my docker-compose file:
version: '3.4'
services:
mssql.db.posm:
image: "microsoft/mssql-server-linux"
environment:
SA_PASSWORD: "mypassword"
ACCEPT_EULA: "Y"
MSSQL_PID: "Express"
volumes:
- mssql-data:/var/opt/mssql
ports:
- "1433:1433"
networks:
posm:
api.posm:
image: ${DOCKER_REGISTRY}posm.api
build:
context: .
dockerfile: Posm.Api/Dockerfile
expose:
- "6869"
ports:
- "6869:80"
networks:
posm:
cloud.subscription:
image: ${DOCKER_REGISTRY}cloud.subscription
build:
context: ./Services
dockerfile: Cloud.Subscription/Dockerfile
ports:
- "80"
networks:
posm:
catalogmanager.services.posm:
image: ${DOCKER_REGISTRY}posm.services.catalogmanager
build:
context: ./Services
dockerfile: CatalogManager/Dockerfile
ports:
- "80"
networks:
posm:
aliases:
- services.posm
- catalogmanager
productmanager.services.posm:
image: ${DOCKER_REGISTRY}posm.services.productmanager
build:
context: ./Services
dockerfile: ProductManager/Dockerfile
ports:
- "80"
networks:
posm:
aliases:
- services.posm
- productmanager
localizer.services.posm:
image: ${DOCKER_REGISTRY}posm.services.localizer
build:
context: ./Services
dockerfile: Localizer/Dockerfile
ports:
- "80"
networks:
posm:
aliases:
- services.posm
- localizer
networks:
posm:
volumes:
mssql-data:
So, when I connect to the api.posm, the latter is able to successfully connect to mssql.db.posm and to cloud.subscription. It however fails, with a connection refused error, to connect to 'catalogmanager' and 'productmanager', even though I can resolve their hostname from within api.posm... What is happening?

Answer 1

You are giving the alias services.posm both to 'catalogmanager' and 'productmanager':
posm:
aliases:
- services.posm
- catalogmanager
As you now per the documentation (https://docs.docker.com/compose/compose-file/#aliases), this will give the hostname "services.posm" to the containers in the posm network. This means that you are having 2 times the "services.posm" host in the network, and both exposing the port 80. This will not work. Remove the "services.posm" line on both containers aliases, restart and you will be able of accessing them using the catalogmanager and productmanager hosts.

Answer 2

So, the problem was a stack overflow exception in one of my images that was unhandled by my debugger, and that I therefore did not see.
Concerning your answer, Moreno...
You are giving the alias services.posm both to 'catalogmanager' and
'productmanager'
I had duplicated this post on Docker forums for increasing my chances to get a relevant answer, and someone suggested the same. The reason I was using the same aliases for three different services is that I read somewhere (cannot find it now, of course) that you could tag multiple services with the same alias for discovery purposes. I probably got that wrong but Docker doesn't seem to mind at all anyways.
So, thanks for your time nonetheless, sorry that I bothered for such stupid mishandling of my code.
Bottom line is: DOCKER ROCKS