How to connect to a remote service from a Docker Container - docker

Question

My dotnet core app running in a docker container on my needs to connect to some external service via their IP one of which is an sql database running separately on a remote server hosted on google cloud. The app runs without issue when not running with docker, however with docker it fails with
An error occurred using the connection to database 'PartnersDb' on server '30.xx.xx.xx,39876'.
fail: Microsoft.EntityFrameworkCore.Update[10000]
An exception occurred in the database while saving changes for context type 'Partners.Api.Infrastructure.Persistence.MoneyTransferDbContext'.
System.InvalidOperationException: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled conn
ections were in use and max pool size was reached.
My Docker compose file looks like this
version: "3.5"
networks:
my-network:
name: my_network
services:
partners:
image: partners.api:latest
container_name: partners
build:
context: ./
restart: always
ports:
- "8081:80"
environment:
- ASPNETCORE_ENVIRONMENT=Docker
- ConnectionStrings:DefaultConnection=Server=30.xx.xx.xx,39876;Database=PartnersDb;User Id=don;Password=Passwor123$$
networks:
- my-network
volumes:
- /Users/mine/Desktop/logs⁩:/logs
I have
bin bashed into the running container and I'm able to run pings to
the remote sql database server
I've also being able to telnet to
the remote sql database server on the database port
However, problem arises when i do docker-compose up then I get the error above.
Docker version 19.03.5, build 633a0ea is running on MacOS Mojave 10.14.6
I really do not know what to do at this stage.

Answer 1

There are two separate networks. Inside docker is a separate network. Outside docker, on the host machine, it's a different network. If you are accessing it by localhost or IP address it won't work as you are expecting it.
docker network ls
will show you a similar output like below:
NETWORK ID NAME DRIVER SCOPE
58a4dd9893e9 133_default bridge local
424817227b42 bridge bridge local
739297b8107e host host local
b9c4fb3ed4ba none null local
You need to add the host for Java service locally. Try running like a below command:
For Service:
docker run --add-host remoteservice:<ip address of java service> <your image>
Hopefully, this will fix it.
More here: https://docs.docker.com/engine/reference/run/#managing-etchosts
For PartnersDb Database:
If PartnersDb is a SQL database you'll have to configure SQL Server to listen to specific ports. Through SQL Server Configuration Manager > SQL Server Network configuration > TCP/IP Properties.
More here: https://learn.microsoft.com/en-us/sql/database-engine/configure-windows/configure-a-server-to-listen-on-a-specific-tcp-port?view=sql-server-ver15
There are similar settings for MySQL as well.
After which you'll have to run add-host switch
docker run --add-host PartnersDb:<ip address of PartnersDb database> <your image>
You can update the hosts file as well with these settings. I'd prefer it through the command line instead.