I am trying to set up a docker for golang app with Postgres.
The go app works fine in a container if I remove/comment Postgres. And similarly, I am able to spin up Postgres container and log into it. I am able do docker-compose up.
But when I make a API call, like for eg: `localhost:3000/api/admin/users`. It gives and error:

```
error: {
        "error": "+dial tcp 127.0.0.1:5432: connect: connection refused"
    }

```

The Postgres connection string is like this: 

```
connStr := fmt.Sprintf("host=postgres user=anurag password=anu_12345 dbname=bankingapp sslmode=disable")

```

db, err := sql.Open("postgres", connStr)

Dockerfile

```
FROM golang:1.13

WORKDIR /go/src/banking-app
COPY . .

RUN go get -d -v ./...
RUN go install -v ./...

CMD ["go" , "run", "main.go"]

```

docker-compose.yml

```
version: '3'
services:
  web:
    build: .
    ports:
      - "3000:3000"
  postgres:
    image: "postgres"
    environment:
      POSTGRES_USER: 'anurag'
      POSTGRES_PASSWORD: 'anu_12345'
      POSTGRES_DB: 'bankingapp'

```