nsswitch / netdns

Dockerfile

FROM golang:1 as builder

COPY . /src
WORKDIR /src

RUN go build -o /src/test
RUN /src/test

main.go

package main

import (
    "net"
    "fmt"
    "os"
)

func main() {

    f, err := os.OpenFile("/Users/tvon/hosts", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
    defer f.Close()
    _, err = f.WriteString("\n127.0.0.1 totally-legit.website")
    if err != nil {
        fmt.Println(err)
    }

    conn, err := net.LookupHost("totally-legit.website")
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(conn)
}

Fails as expected (ignoring /etc/hosts):

❯ docker build -t foobar .
Sending build context to Docker daemon  3.072kB
Step 1/5 : FROM golang:1 as builder
 ---> 5fbd6463d24b
Step 2/5 : COPY . /src
 ---> a49283d30be7
Step 3/5 : WORKDIR /src
 ---> Running in db79ff4629e1
Removing intermediate container db79ff4629e1
 ---> 043be4e3a602
Step 4/5 : RUN go build -o /src/test
 ---> Running in 9d8dd5fa1c48
Removing intermediate container 9d8dd5fa1c48
 ---> 53f0640c08b6
Step 5/5 : RUN /src/test
 ---> Running in 4e156a882332
invalid argument
lookup totally-legit.website on 192.168.65.1:53: no such host
[]
Removing intermediate container 4e156a882332
 ---> 3af9bdcb7795
Successfully built 3af9bdcb7795
Successfully tagged foobar:latest