Why docker build flag --add-host is not working on linux ubuntu ?

Question

I am trying to run my docker development setup and I can't access host from

docker build --add-host mymachinelocalip:ss-local

in my production ubuntu envrionment, by caling in Dockerfile:

RUN curl -f http://ss-local:8181

my /etc/hosts :

::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.1  ss-local
172.17.0.5  e1ede117fb1e

On my local computer (MacOSX El Capitan and Windows10) everything works perfect.. But on digitalocean droplet with Ubuntu curl command fail.

I am beginer with docker.. and I am wondering maybe there is some kind of firewall on linux that prevent connections to host...

Ubuntu 16.04.2 LTS with Docker version 17.06.0-ce, build 02c1d87.

Do you get the same issue if the --add-host mapping is done at run time and using an IP address different then the docker0 interface. i(ie: docker run -ti --add-host "ss-local:192.168.120.154" ubuntu bash) — lvolmar
– lvolmar, Commented Jul 11, 2017 at 20:23

Charlie Flowers · Accepted Answer · 2018-04-17 16:21:51Z

4

When you pass --add-host to docker build, the host is only added during the build. If you pass --add-host to docker run, the host will be present at runtime.

Reference: https://github.com/moby/moby/pull/30383#issuecomment-314797629

answered Apr 17, 2018 at 16:21

Charlie Flowers

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