Using --add-host or extra_hosts with docker-compose

Question

I am using docker-compose to run a test environment, that consists of about 5 different containers. The inter-container links and the shared volumes (volumes-from) works wonderfully. I also expose some ports up to the host machine, which works nicely.

What I am missing is a way to link some of my real servers into this environment, without hardcoding ip address. With docker run, you could use --add-host to add another line in your /etc/hosts file. Is there any way to do something similar with docker-compose?

oneklc · Answer 1 · 2021-03-10T03:08:34.373

155

https://github.com/compose-spec/compose-spec/blob/master/spec.md#extra_hosts

extra_hosts - Add hostname mappings. Uses the same values as the docker client --add-host parameter.

extra_hosts:
 - "somehost:162.242.195.82"
 - "otherhost:50.31.209.229"

An entry with the ip address and hostname will be created in /etc/hosts > inside containers for this service, e.g:

162.242.195.82  somehost
50.31.209.229   otherhost

edited Mar 10 '21 at 03:08

answered Oct 23 '15 at 22:26

oneklc

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Not supported on build – expelledboy Jun 06 '17 at 14:28
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How can I map an external name (not an IP) to a container alias? – Adriano dos Santos Fernandes Dec 28 '17 at 13:02
You mean set a hostname? -h HOSTNAME https://docs.docker.com/engine/userguide/networking/default_network/configure-dns/ Or use an alias in docker-compose: https://docs.docker.com/compose/compose-file/#aliases – oneklc Jan 05 '18 at 19:47
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`extra_hosts` appears to be supported as an undocumented subkey of `build`, at least on compose 2.4.1. – J Cracknell Feb 07 '23 at 17:30
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It should be also supported on build now: https://github.com/compose-spec/compose-spec/blob/master/build.md#extra_hosts – solosuper May 07 '23 at 22:51

score 136 · Accepted Answer · edited Aug 29 '23 at 04:15

136

This works still docker-compose 1.3 with extra_hosts parameter:

rng:
  build: rng
  extra_hosts:
    seed: 1.2.3.4
    tree: 4.3.2.1

edited Aug 29 '23 at 04:15

Gilles Quénot

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answered May 30 '15 at 01:56

jpetazzo

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For any one finding this to error out saying unsupported config directive "extra-hosts" it's not "extra-hosts" it's "extra_hosts". – Prasanth Jan 15 '19 at 12:11
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The format here, of a nested dictionary, is out of date. This answer https://stackoverflow.com/a/61231167/1497199 is more up to date. – Dave Dec 02 '21 at 01:38
@Dave No, it is NOT out of date. If you should have the wrong format, docker-compose will tell you: `services.imageproxy.extra_hosts contains an invalid type, it should be an object, or an array`. And `object` is one of two options. Far preferrable to a string, IMHO. – oligofren Dec 03 '21 at 06:56
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i have added this `extra_hosts: - "host.docker.internal:host-gateway"` but still it is saying in logs that connection refused – Sunil Garg Aug 09 '22 at 09:42

score 92 · Answer 3 · edited Dec 02 '21 at 01:40

Basic docker-compose.yml with extra hosts:

version: '3'
services:
api:
    build: .
    ports:
        - "5003:5003"
    extra_hosts:
        - "your-host.name.com:162.242.195.82" #host and ip
        - "your-host--1.name.com your-host--2.name.com:50.31.209.229" #multiple hostnames with same ip

The content in the /etc/hosts file in the created container:

162.242.195.82  your-host.name.com
50.31.209.229   your-host--1.name.com your-host--2.name.com

You can check the /etc/hosts file with the following commands:

$ docker-compose -f path/to/file/docker-compose.yml run api bash  # 'api' is service name
#then inside container bash
root@f7c436910676:/app# cat /etc/hosts

IMHO this should be the top answer -- the other higher-voted answers are a bit out of date. — Dave, Dec 02 '21 at 01:41

Using --add-host or extra_hosts with docker-compose

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