sqlx.Connect() get stuck in docker alpine:latest - postgresql

Question

I have problem that I've managed to reduce to the following code:
package main
import (
"fmt"
"github.com/jmoiron/sqlx"
_ "github.com/lib/pq"
"os"
)
func main() {
addr := os.Getenv("DB")
fmt.Println("Postgres addr: " + addr)
_, err := sqlx.Connect("postgres", addr)
if err != nil {
fmt.Println("Could not connect...")
} else {
fmt.Println("Connecting successful")
}
}
I set up a repo with the code and more explanations at:
https://github.com/mraxus/mystery-golang-alpine
When I build and run this Go code with a valid DB url in a docker image (here golang:latest) throught docker-compose, where both the above program and the postgres db is in separate containers, the program runs as expected:
build_1 | Postgres addr: postgres://postgres#postgres/postgres?sslmode=disable
build_1 | Connecting successful
However, when I run the same program in same setup (docker-compose) with the base image alpine:latest, the program just gets stuck at the sqlx.Connect():
alpine_1 | Postgres addr: postgres://postgres#postgres/postgres?sslmode=disable
I have no idea why this is. Do you know? I have setup a project to see if others can reproduce and get the same problem as I get:
https://github.com/mraxus/mystery-golang-alpine
Love to hear some insights that can help me solve this issue.
My system details:
macOS 10.12.6 (Sierra, MBP Mid 2015 15-inch)
docker 17.06.1 1-ce-mac24

Answer 1

Proper solution (by realizing the actual problem)
So it turns out that the corporate network at work have a search domain set. This affects the alpine containers name resolution. However, the default golang is not.
To solve the problem, you can overwrite docker-compose containers search domain, by modifying the config:
build:
dns_search: .
image: image:build
...
alpine:
dns_search: .
image: image:alpine
...
See https://github.com/mraxus/mystery-golang-alpine/pull/4
Alternative solution (not having realized the actual problem)
By forcing go to use the cgo name resolver, there is no longer any issues:
In docker-compose.yml
alpine:
image: mamarcus.org/project:alpine
links:
- postgres
environment:
DB: "postgres://postgres#postgres/postgres?sslmode=disable"
GODEBUG: "netdns=cgo"
See https://github.com/mraxus/mystery-golang-alpine/pull/3
It should be mentioned that this solution is still iffy. In our real dev environment, containing ~20 services configured in docker-compose, some docker alpine images still did not resolve properly. But when updating the configuration with the "proper solution", everything worked like a charm.