How to communicate between Docker containers via hostname

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     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

User · Answer

As far as I know  by using only Docker this is not possible  You need some DNS to map container ip s to hostnames    If you want out of the box solution  One solution is to use for example Kontena  It comes with network overlay technology from Weave and this technology is used to create virtual private LAN networks for each service and every service can be reached by service name kontena local-address   Here is simple example of Wordpress application s YAML file where Wordpress service connects to MySQL server with wordpress-mysql kontena local address   wordpress                                                                             image  wordpress 4 1                                                                stateful  true                                                                      ports                                                                                 - 80 80                                                                         links                                                                                 - mysql wordpress-mysql                                                           environment                                                                           - WORDPRESS DB HOST wordpress-mysql kontena local                                   - WORDPRESS DB PASSWORD secret                                                  mysql                                                                                 image  mariadb 5 5                                                                  stateful  true                                                                      environment                                                                           - MYSQL ROOT PASSWORD secret

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That should be what --link is for  at least for the hostname part  With docker 1 10  and PR 19242  that would be   docker network create --net-alias     Add network-scoped alias for the container    see last section below   That is what Updating the  etc hosts file details     In addition to the environment variables  Docker adds a host entry for the source container to the  etc hosts file    For instance  launch an LDAP server   docker run -t  --name openldap -d -p 389 389 larrycai openldap   And define an image to test that LDAP server   FROM ubuntu RUN apt-get -y install ldap-utils RUN touch  root  bash aliases RUN echo  alias lds  ldapsearch -H ldap   internalopenldap -LL -b ou Users dc openstack dc org -D cn admin dc openstack dc org -w password    gt   root  bash aliases ENTRYPOINT bash   You can expose the  openldap  container as  internalopenldap  within the test image with --link    docker run -it --rm --name ldp --link openldap internalopenldap ldaptest   Then  if you type  lds   that alias will work   ldapsearch -H ldap   internalopenldap       That would return people  Meaning internalopenldap is correctly reached from the ldaptest image     Of course  docker 1 7 will add libnetwork  which  provides a native Go implementation for connecting containers  See the blog post  It introduced a more complete architecture  with the Container Network Model  CNM     That will Update the Docker CLI with new    network    commands  and document how the    -net    flag is used to assign containers to networks     docker 1 10 has a new section Network-scoped alias  now officially documented in network connect      While links provide private name resolution that is localized within a container  the network-scoped alias provides a way for a container to be discovered by an alternate name by any other container within the scope of a particular network    Unlike the link alias  which is defined by the consumer of a service  the network-scoped alias is defined by the container that is offering the service to the network       Continuing with the above example  create another container in isolated nw with a network alias      docker run --net isolated nw -itd --name container6 -alias app busybox 8ebe6767c1e0361f27433090060b33200aac054a68476c3be87ef4005eb1df17  --alias                  Add network-scoped alias for the container      You can use --link option to link another container with a preferred alias      You can pause  restart  and stop containers that are connected to a network  Paused containers remain connected and can be revealed by a network inspect  When the container is stopped  it does not appear on the network until you restart it       If specified  the container s IP address es  is reapplied when a stopped container is restarted  If the IP address is no longer available  the container fails to start        One way to guarantee that the IP address is available is to specify an --ip-range when creating the network  and choose the static IP address es  from outside that range  This ensures that the IP address is not given to another container while this container is not on the network      docker network create --subnet 172 20 0 0 16 --ip-range 172 20 240 0 20 multi-host-network    docker network connect --ip 172 20 128 2 multi-host-network container2   docker network connect --link container1 c1 multi-host-network container2

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The new networking feature allows you to connect to containers by their name  so if you create a new network  any container connected to that network can reach other containers by their name  Example   1  Create new network    docker network create  lt network-name gt           2  Connect containers to network    docker run --net  lt network-name gt        or    docker network connect  lt network-name gt   lt container-name gt    3  Ping container by name  docker exec -ti  lt container-name-A gt  ping  lt container-name-B gt    64 bytes from c1  172 18 0 4   icmp seq 1 ttl 64 time 0 137 ms 64 bytes from c1  172 18 0 4   icmp seq 2 ttl 64 time 0 073 ms 64 bytes from c1  172 18 0 4   icmp seq 3 ttl 64 time 0 074 ms 64 bytes from c1  172 18 0 4   icmp seq 4 ttl 64 time 0 074 ms   See this section of the documentation    Note  Unlike legacy links the new networking will not create environment variables  nor share environment variables with other containers   This feature currently doesn t support aliases

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EDIT   It is not bleeding edge anymore   http   blog docker com 2016 02 docker-1-10   Original Answer I battled with it the whole night  If you re not afraid of bleeding edge  the latest version of Docker engine and Docker compose both implement libnetwork   With the right config file  that need to be put in version 2   you will create services that will all see each other  And  bonus  you can scale them with docker-compose as well  you can scale any service you want that doesn t bind port on the host   Here is an example file  version   2  services    router      build  services router      ports        -  8080 8080    auth      build  services auth    todo      build  services todo    data      build  services data    And the reference for this new version of compose file  https   github com docker compose blob 1 6 0-rc1 docs networking md

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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 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  gt  amp 2             echo  host-record  name  ip    gt     DNSMASQ CONFIG  docker- name              changed true         fi     done  lt   lt    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

[networking] How to communicate between Docker containers via "hostname"

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