Access docker container from host using containers name

There is a opensource application that solves this issue, it's called DNS Proxy Server, here some examples from official repository

It's a DNS server that solves containers hostnames, if could not found a hostname that matches then solve it from internet as well

Start DNS Server

$ docker run --hostname dns.mageddo --restart=unless-stopped -p 5380:5380 \
-v /var/run/docker.sock:/var/run/docker.sock \
-v /etc/resolv.conf:/etc/resolv.conf \
defreitas/dns-proxy-server

It will be set automatically as your default DNS (and recover to the original when it stops)

Creating some containers for test

checking docker-compose file

$ cat docker-compose.yml
version: '3'
services:
  nginx-1:
    image: nginx
    hostname: nginx-1.docker
    network_mode: bridge 
  linux-1:
    image: alpine
    hostname: linux-1.docker
    command: sh -c 'apk add --update bind-tools && tail -f /dev/null'
    network_mode: bridge # that way he can solve others containers names even inside, solve nginx-2, for example

starting containers

$ docker-compose up

Solving containers

from host

nslookup nginx-1.docker
Server:     13.0.0.5
Address:    13.0.0.5#53
Non-authoritative answer:
Name:   nginx-1.docker
Address: 13.0.0.6

from another container

$ docker-compose exec linux-1 ping nginx-1.docker
PING nginx-1.docker (13.0.0.6): 56 data bytes
64 bytes from 13.0.0.6: seq=0 ttl=64 time=0.034 ms

As well it solves internet hostnames

$ nslookup google.com
Server:     13.0.0.5
Address:    13.0.0.5#53

Non-authoritative answer:
Name:   google.com
Address: 216.58.202.78

If you're only using you docker-compose setup locally you could map the ports from your containers to your host with

elasticsearch:
  image: elasticsearch:2.2
  ports:
    - 9300:9300
    - 9200:9200

Then use localhost:9300 (or 9200 depending on protocol) from your web-app to access Elasticsearch.

A more complex solution is to run your own dns that resolve container names. I think that this solution is a lot closer to what you're asking for. I have previsously used skydns when running kubernetes locally.

There are a few options out there. Have a look at https://github.com/gliderlabs/registrator and https://github.com/jderusse/docker-dns-gen. I didn't try it, but you could potentially map the dns port to your host in the same way as with the elastic ports in the previous example and then add localhost to your resolv.conf to be able to resolve your container names from your host.

There are two solutions (except /etc/hosts) described here and here

I wrote my own solution in Python and implemented it as service to provide mapping from container hostname to its IP. Here it is: https://github.com/nicolai-budico/dockerhosts

It launches dnsmasq with parameter --hostsdir=/var/run/docker-hosts and updates file /var/run/docker-hosts/hosts each time a list of running containers was changed. Once file /var/run/docker-hosts/hosts is changed, dnsmasq automatically updates its mapping and container become available by hostname in a second.

$ docker run -d --hostname=myapp.local.com --rm -it ubuntu:17.10
9af0b6a89feee747151007214b4e24b8ec7c9b2858badff6d584110bed45b740

$ nslookup myapp.local.com
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   myapp.local.com
Address: 172.17.0.2

There are install and uninstall scripts. Only you need is to allow your system to interact with this dnsmasq instance. I registered in in systemd-resolved:

$ cat /etc/systemd/resolved.conf

[Resolve]
DNS=127.0.0.54
#FallbackDNS=
#Domains=
#LLMNR=yes
#MulticastDNS=yes
#DNSSEC=no
#Cache=yes
#DNSStubListener=udp

I'm using a bash script to update /etc/hosts. Why this solution?

• Short script, easy to review (didn't want to give some un-reviewed application with lots of dependencies access to the Docker socket (which means root access))
• It uses docker events to run every time a container is started or stopped (other solutions posted here run every second in a loop, which is way less efficient)
• Updates /etc/hosts, no separate DNS server needed.
• Only dependencies are bash, mktemp, grep, xargs, sed, jq and docker, all of which I had already installed.

Just put the script somewhere, e.g. /usr/local/bin/docker-update-hosts:

#!/usr/bin/env bash
set -e -u -o pipefail

hosts_file=/etc/hosts
begin_block="# BEGIN DOCKER CONTAINERS"
end_block="# END DOCKER CONTAINERS"

if ! grep -Fxq "$begin_block" "$hosts_file"; then
    echo -e "\n${begin_block}\n${end_block}\n" >> "$hosts_file"
fi

(echo "| container start |" && docker events) | \
while read event; do
    if [[ "$event" == *" container start "* ]] || [[ "$event" == *" network disconnect "* ]]; then
        hosts_file_tmp="$(mktemp)"
        docker container ls -q | xargs -r docker container inspect | \
        jq -r '.[]|"\(.NetworkSettings.Networks[].IPAddress|select(length > 0) // "# no ip address:") \(.Name|sub("^/"; "")|sub("_1$"; ""))"' | \
        sed -ne "/^${begin_block}$/ {p; r /dev/stdin" -e ":a; n; /^${end_block}$/ {p; b}; ba}; p" "$hosts_file" \
        > "$hosts_file_tmp"
        chmod 644 "$hosts_file_tmp"
        mv "$hosts_file_tmp" "$hosts_file"
    fi
done

Note: The script removes the _1 suffix added by docker-compose from container names. If you don't want that just remove |sub("_1$"; "") from the script.

You can use a systemd service to run this synchronously with Docker: /etc/systemd/system/docker-update-hosts.service:

[Unit]
Description=Update Docker containers in /etc/hosts
Requires=docker.service
After=docker.service
PartOf=docker.service

[Service]
ExecStart=/usr/local/bin/docker-update-hosts

[Install]
WantedBy=docker.service

To activate, run:

systemctl daemon-reload
systemctl enable docker-update-hosts.service
systemctl start docker-update-hosts.service