How to communicate between Docker containers via "hostname"

ghz 1years ago ⋅ 8561 views

Question

I plan to split my monolthic server up into many small docker containers but haven't found a good solution for "inter-container communication" yet. This is my target scenario:

Target scenario

I know how to link containers together and how to expose ports, but none of these solutions are satisfying to me.

Is there any solution to communicate via hostnames (container names) between the containers like in a traditional server network?

Answer

Edit: After Docker 1.9, the docker network command (see below https://stackoverflow.com/a/35184695/977939) is the recommended way to achieve this.

My solution is to set up a dnsmasq on the host to have DNS record automatically updated: "A" records have the names of containers and point to the IP addresses of the containers automatically (every 10 sec). The [automatic updating script](http://docs.blowb.org/appendices/update- dnsmasq.html) is pasted here:

#!/bin/bash

# 10 seconds interval time by default
INTERVAL=${INTERVAL:-10}

# dnsmasq config directory
DNSMASQ_CONFIG=${DNSMASQ_CONFIG:-.}

# commands used in this script
DOCKER=${DOCKER:-docker}
SLEEP=${SLEEP:-sleep}
TAIL=${TAIL:-tail}

declare -A service_map

while true
do
    changed=false
    while read line
    do
        name=${line##* }
        ip=$(${DOCKER} inspect --format '{{.NetworkSettings.IPAddress}}' $name)
        if [ -z ${service_map[$name]} ] || [ ${service_map[$name]} != $ip ] # IP addr changed
        then
            service_map[$name]=$ip
            # write to file
            echo $name has a new IP Address $ip >&2
            echo "host-record=$name,$ip"  > "${DNSMASQ_CONFIG}/docker-$name"
            changed=true
        fi
    done < <(${DOCKER} ps | ${TAIL} -n +2)

    # a change of IP address occured, restart dnsmasq
    if [ $changed = true ]
    then
        systemctl restart dnsmasq
    fi

    ${SLEEP} $INTERVAL
done

Make sure your dnsmasq service is available on docker0. Then, start your container with --dns HOST_ADDRESS to use this mini dns service.

Reference: http://docs.blowb.org/setup-host/dnsmasq.html

#docker