Connection issue with golang microservice to database microservice - docker

Question

I have a Golang project I am working and have multiple micro-services in the same code repository. My directory structure is roughly as follows:
├── pkg
├── cmd
│ ├── servicea
│ └── serviceb
├── internal
│ ├── servicea
│ └── serviceb
├── Makefile
├── scripts
│ └── protogen.sh
├── vendor
│ └── ...
├── go.mod
├── go.sum
└── readme.md
The main.go files for the respective services are in cmd/servicex/main.go
I've put the individual Dockerfiles for the services in cmd/servicex.
Roughly, this is how my Dockerfile looks like:
FROM golang:1.15.6
ARG version
COPY go.* <repo-path>
COPY pkg/ <repo-path>/pkg/
COPY internal/servicea internal/servicea
COPY vendor/ <repo-path>/vendor/
COPY cmd/servicea/ <repo-path>/cmd/servicea/
WORKDIR <repo-path>/cmd/servicea/
RUN GO111MODULE=on GOFLAGS=-mod=vendor CGO_ENABLED=0 GOOS=linux go build -v -ldflags "-X <repo-path>/cmd/servicea/main.version=$version" -a -installsuffix cgo -o servicea .
FROM alpine:3.12
RUN apk --no-cache add ca-certificates
WORKDIR /servicea/
COPY --from=0 <repo-path>/cmd/servicea .
EXPOSE 50051
ENTRYPOINT ["/servicea/servicea"]
I am using Scylla as my DB for this service and gRPC is the protocol for communication.
This is my docker-compose.yml for this service.
version: '3'
services:
db:
container_name: servicedb
image: scylladb/scylla
hostname: db
environment:
GET_HOST_FROM: dns
SCYLLA_USER: <user>
SCYLLA_PASS: <password>
ports:
- 9042:9042
networks:
- serviceanet
servicea:
container_name: servicea
image: servicea-production:latest
hostname: servicea
build:
context: .
dockerfile: Dockerfile
environment:
GET_HOSTS_FROM: dns
networks:
- serviceanet
volumes:
- .:<repo-path>
ports:
- 50051:50051
depends_on:
- db
links:
- db
labels:
kompose.service.type: LoadBalancer
networks:
serviceannet:
driver: bridge
I am using kompose to generate the corresponding kubernetes yaml files.
However, when I run the compose locally or try to deploy it on minikube/GKE, my service instance is not able to connect to my DB and I get an error like this:
failed to create scylla session, gocql: unable to create session: control: unable to connect to initial hosts: dial tcp 127.0.0.1:9042: connect: connection refused
Otherwise, if I run a local scylla docker instance with the following command:
docker run --name some-scylla -p 9042:9042 -d scylladb/scylla --broadcast-address 127.0.0.1 --listen-address 0.0.0.0 --broadcast-rpc-address 127.0.0.1
and then do a go run cmd/servicea/main.go my service seems to be running and the API endpoints are working(verified with Evans).

Answer 1

127.0.0.1 (localhost) is the host/container on which your service is running. in the case of multiple containers (either using docker-compose or k8s) they would have different IP addresses and 127.0.0.1 would correspond to different hosts depending where you are connecting from. In your gocql initialization, provide the db address using a configuration/environment variable. docker-compose will automatically configure a hostname for the db container and with k8s you can use its service discovery mechanism.