Use hosts file from aerokube/selenoid for browser containers

[egormkn]

I am trying to set up selenoid to test an application started on localhost. I've tried using --net=host with -container-network host, but this did't work for me (4444 port was not bound for some reason). Docker also has --add-host="host.docker.internal:host-gateway" argument that adds the host IP to /etc/hosts in container, so it is possible to connect to host from within the aerokube/selenoid container started with this argument. However, it seems that browser containers do not know about this configuration and I didn't find a way to modify their launch arguments to pass it.

I suggest to add some way for browser containers to use the hosts defined in selenoid container.

[vania-pooh]

@egormkn this is implemented years ago:

1. Selenoid has hosts section in browsers.json: https://aerokube.com/selenoid/latest/#_other_optional_fields
2. Docker has built-in aliases for host machine. https://stackoverflow.com/questions/22944631/how-to-get-the-ip-address-of-the-docker-host-from-inside-a-docker-container/45002996#45002996

[egormkn]

1. Selenoid has hosts section in browsers.json: https://aerokube.com/selenoid/latest/#_other_optional_fields

It requires static IP, while I want to use the local IP of my laptop. It might change depending on the network I am connected to.

2. Docker has built-in aliases for host machine. https://stackoverflow.com/questions/22944631/how-to-get-the-ip-address-of-the-docker-host-from-inside-a-docker-container/45002996#45002996

That is exactly the thing that does not work: host.docker.internal is properly resolved to local IP for aerokube/selenoid container but not for browser containers (selenoid/firefox, selenoid/chrome etc.).

I am using Docker v20.10 on Ubuntu 20.04. Maybe for Windows and MacOS that alias is automatically resolved for all docker containers. On Linux it should be passed as command-line argument for docker run.

[vania-pooh]

@egormkn Docker is using a dedicated network adapter (docker0) and thus gateway IP address does no change.

[ruslanshelar]

@vania-pooh hello I have the same problem. I try to run specs using selenoid. Selenoid runs locally in docker. The application runs locally too but not in docker (on 127.0.0.1:9887). What should I set in hosts to make access from browser containers to my app?

ifconfig docker0
docker0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 100.64.0.1  netmask 255.255.0.0  broadcast 100.64.255.255
        inet6 fe80::42:ebff:fedd:8323  prefixlen 64  scopeid 0x20<link>
        ether 02:42:eb:dd:83:23  txqueuelen 0  (Ethernet)
        RX packets 1120728  bytes 715089890 (715.0 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1245247  bytes 418069136 (418.0 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[vania-pooh]

@ruslanshelar usually going to 100.64.0.1:9887 should help.

[ruslanshelar]

@vania-pooh what do u mean "going"? I already have tried to open 100.64.0.1:9887 in the browser container and it does not work.

[vania-pooh]

@ruslanshelar going means "establishing TCP connection".

[egormkn]

@vania-pooh I was hoping to get a solution, that would not be tied to specific IP addresses so that it will be reproducible on an arbitrary local machine. As you see, @ruslanshelar has IP 100.64.0.1 assigned to his bridge interface while for me it is 172.17.0.1.

Passing hosts file from selenoid container to browser containers seems to me like a good solution. I couldn't find any other ways to establish TCP connection to localhost without hardcoding the IP.

[Perni1984]

@egormkn how exactly did you pass the host file from the seleonid container to the browser containers? It seems for using the hosts section in browsers.json I would need to manually parse the /etc/hosts file of the selenoid container somehow.

@vania-pooh would it be possible to run the browser containers with the --add-host="host.docker.internal:host-gateway" command line option added?

More info about this option can be found in https://github.com/moby/moby/pull/40007

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