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I have an app in Python that I want to run in a Docker container and it has a line:

h2o.connect(ip='127.0.0.1', port='54321')

The h2o server is running in a Docker container and it always has a different IP. One time it was started on 172.19.0.5, the other time 172.19.0.3, sometimes 172.17.0.3. So it is always random, and I can't connect the Python app. I tried to expose the port of h2o server to localhost and then connect the Python (the code above), but it is not working.

rgettman
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Milan Panic
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  • Possible duplicate of [How to reach docker containers by name instead of IP address?](https://stackoverflow.com/questions/31149501/how-to-reach-docker-containers-by-name-instead-of-ip-address) – David Maze Jul 04 '18 at 10:58

1 Answers1

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You dont connect two docker containers though ip addresses. Instead, you want to use docker internal network aliases: 

version: '3'
services:
  server:
    ...
    depends_on:
      - database
  database:
    ...
    expose:
      - 54321:54321

then you can define your connectio in server as: h2o.connect(ip='127.0.0.1', port='54321')

Simas Joneliunas
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    correction: version: '3' services: server: ... depends_on: - database database: ... expose: - 54321 and h2o.connect(ip='database', port='54321') – cjdcordeiro Jul 04 '18 at 09:02
  • correct me if i am wrong, but i think that `ports:` declaration is sufficient when communicating between two linked docker images. You would want to `expose:` the port only when you want to open the container to external connections? – Simas Joneliunas Jul 04 '18 at 09:09
  • Thank you very much, it worked, I used depends_on: *theThingItDependsOn* and then in my python code I wrote ip=*theThingItDependsOn* – Milan Panic Jul 04 '18 at 10:30
  • But it is programming and now I have a different problem. Now because the h2o server and python are running in the docker, the windows path C:/Desktop/Data/data.csv is not visible, because is somewhere in a container. How do I insert the csv file in the container and specify the path? Do I use volume or is there an easiear solution? – Milan Panic Jul 04 '18 at 10:36
  • you should use a shared volume. that is the easiest solution. You can also insert it when creating the container in `dockerfile` but in that case you would only have a static file that you could only modify by repackaging the container. Alternitively, you can expose the port per @cjdcordeiro advise and create a web api to upload it to the container. This approach would only work while container is alive and the file would be lost unless you implemented volumes. – Simas Joneliunas Jul 04 '18 at 13:19
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    Simas, it's the opposite. "ports" will publish the port to the host - that's why the format is "dest:source" – cjdcordeiro Jul 05 '18 at 08:40
  • seems I also learnt something new from this question. Thanks for clarifying! – Simas Joneliunas Jul 05 '18 at 08:42