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

User · Answer

Basic docker-compose yml with extra hosts  version   3  services  api      build        ports          -  quot 5003 5003 quot      extra hosts          -  quot your-host name com 162 242 195 82 quot   host and ip         -  quot your-host--1 name com your-host--2 name com 50 31 209 229 quot   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

User · Answer

It seems like it should be made possible to say  extra hosts   -  quot loghost localhost quot   So if the part after the colon  normally an IP address  doesn t start with a digit  then name resolution will be performed to look up an IP for localhost  and add something like to the container s  etc hosts  127 0 0 1 loghost    assuming that localhost resolves to 127 0 0 1 on the host system  It looks like it d be really easy to add in docker-compose s source code  compose config types py s parse extra hosts function would likely do it  For docker itself  this would probably be addable in opts hosts go s ValidateExtraHost function  though then it s not strictly validating anymore  so the function would be a little misnamed  It might actually be a little better to add this to docker  not docker-compose - docker-compose might just get it automatically if docker gets it  Sadly  this would probably require a container bounce to change an IP address

User · Answer

https   docs docker com compose compose-file  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

User · Answer

I have great news  this will be in Compose 1 3  I m using it in the current RC  RC1  like this  rng    build  rng   extra hosts      seed  1 2 3 4     tree  4 3 2 1

User · Answer

This is in the feature backlog for Compose but it doesn t look like work has been started yet  Github issue

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

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