Container on same network not communicating with each other - mongodb

Question

I have a mongodb container which i name e-learning
and i have a docker image which should connect to the mongodb container to update my database but it's not working i get this error:
Unknown, Last error: connection() error occurred during connection handshake: dial tcp 127.0.0.1:27017: connect: connection refused }
here's my docker build file
# syntax=docker/dockerfile:1
FROM golang:1.18
WORKDIR /go/src/github.com/worker
COPY go.mod go.sum main.go ./
RUN go mod download
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app .
FROM jrottenberg/ffmpeg:4-alpine
FROM alpine:latest
RUN apk --no-cache add ca-certificates
WORKDIR /root/
ENV LD_LIBRARY_PATH=/usr/local/lib
COPY --from=jrottenberg/ffmpeg / /
COPY app.env /root
COPY --from=0 /go/src/github.com/worker/app .
CMD ["./app"]
my docker compose file
version: "3.9"
services:
worker:
image: worker
environment:
- MONGO_URI="mongodb://localhost:27017/"
- MONGO_DATABASE=e-learning
- RABBITMQ_URI=amqp://user:password#rabbitmq:5672/
- RABBITMQ_QUEUE=upload
networks:
- app_network
external_links:
- e-learning
- rabbitmq
volumes:
- worker:/go/src/github.com/worker:rw
networks:
app_network:
external: true
volumes:
worker:
my docker inspect network
[
{
"Name": "app_network",
"Id": "f688edf02a194fd3b8a2a66076f834a23fa26cead20e163cde71ef32fc1ab598",
"Created": "2022-06-27T12:18:00.283531947+03:00",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "172.20.0.0/16",
"Gateway": "172.20.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"2907482267e1f6e42544e5e8d852c0aac109ec523c6461e003572963e299e9b0": {
"Name": "rabbitmq",
"EndpointID": "4b46e091e4d5a79782185dce12cb2b3d79131b92d2179ea294a639fe82a1e79a",
"MacAddress": "02:42:ac:14:00:03",
"IPv4Address": "172.20.0.3/16",
"IPv6Address": ""
},
"8afd004a981715b8088af53658812215357e156ede03905fe8fdbe4170e8b13f": {
"Name": "e-learning",
"EndpointID": "1c12d592a0ef6866d92e9989f2e5bc3d143602fc1e7ad3d980efffcb87b7e076",
"MacAddress": "02:42:ac:14:00:02",
"IPv4Address": "172.20.0.2/16",
"IPv6Address": ""
},
"ad026f7e10c9c1c41071929239363031ff72ad1b9c6765ef5c977da76f24ea31": {
"Name": "video-transformation-worker-1",
"EndpointID": "ce3547014a6856725b6e815181a2c3383d307ae7cf7132e125c58423f335b73f",
"MacAddress": "02:42:ac:14:00:04",
"IPv4Address": "172.20.0.4/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {}
}
]

Answer 1

Change MONGO_URI="mongodb://localhost:27017/" to MONGO_URI="mongodb://e-learning:27017/" (working on the assumption that e-learning is the mongo container).
Within a container attached to a bridge network (the default) localhost (127.0.0.1) is the container itself. So your app container is trying to access the database at port 27017 on itself (not on the host or on the db container). The easiest solution is to use the automatic DNS resolution between containers that docker provides.

Answer 2

I added extra hosts and changed my mongo uri to host.docker.internal
and it solved my problems
version: "3.9"
services:
worker:
image: worker
environment:
- MONGO_URI="mongodb://host.docker.internal:27017/"
- MONGO_DATABASE=e-learning
- RABBITMQ_URI=amqp://user:password#rabbitmq:5672/
- RABBITMQ_QUEUE=upload
networks:
- app_network
external_links:
- e-learning
- rabbitmq
volumes:
- worker:/go/src/github.com/worker:rw
extra_hosts:
- "host.docker.internal:host-gateway"
networks:
app_network:
external: true
volumes:
worker: