CODEWITHSUNDEEP
dockerwebsocketdocker-compose
jiboulex
jiboulex

Reputation: 3031

Open a WebSocket connexion from a docker container to another (able to ping container in cli but not via ws)

I'm using docker-compose to run 2 containers, 1 for running a react application and another to run a rabbitmq server.

version: '2'
services:
    node.app.local:
        build:
            context: ./node
        container_name: app-node
        hostname: node.app
        domainname: local
        tty: true
        volumes:
            - "${SOURCES_PATH}/app:/var/www/app"
        ports:
            - 8091:8091
        expose:
            - 8091
        links:
            - rabbitmq.app.local
        working_dir: "/var/www/app"

    rabbitmq.app.local:
        image: rabbitmq:3.6.10
        container_name: app-rabbitmq
        hostname: rabbitmq.app
        domainname: local
        tty: true
        expose:
            - 5672
            - 15672
            - 15674

I know that the link between my node container and my rabbitmq server is working well as I can ping the server from my node container :

$ docker exec -it app-node bash
$ ping rabbitmq.app.local

64 bytes from 172.18.0.12: icmp_seq=0 ttl=64 time=0.099 ms

64 bytes from 172.18.0.12: icmp_seq=1 ttl=64 time=0.098 ms

64 bytes from 172.18.0.12: icmp_seq=2 ttl=64 time=0.069 ms

64 bytes from 172.18.0.12: icmp_seq=3 ttl=64 time=0.088 ms

In my js application, if I open a connection with the IP of the server (172.18.0.12 as exposed by the ping), it works well :

const ws = new WebSocket('ws://172.18.0.12:15674/ws');
//connected to server RabbitMQ/3.6.10

But if I try with the container name :

const ws = new WebSocket('ws://rabbitmq.app.local:15674/ws');

VM7698:35 WebSocket connection to 'ws://rabbitmq.app.local:15674/ws' failed: Error in connection establishment: net::ERR_NAME_NOT_RESOLVED

Does anyone knows why I can ping the server in CLI but can't access it via the ws protocol ?

Upvotes: 4

Views: 5240

Answers (1)

Chad Cai
Chad Cai

Reputation: 31

I ran into the same problem when using PHP in one container connecting to a websocket service in another container.

I did some research, and found that docker compose v2 uses user-defined networks, which in terms introduced an embedded DNS server, replacing the traditional DNS inside a container in the default bridge network.

The embedded DNS server maintains the mapping between all of the container aliases and its IP address on a specific user-defined network.

That how it works, according to docker official document. But it seems that there are some problems when trying to DNS-resolve a container alias or link, said by jake-low, a contributor of docker-compose.

So, an alternative solution to this problem is to get the IP by hostname first, and then use the resolved IP to connect to the websocket service. This is how I solve the problem.

Upvotes: 3

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