Name resolution in custom network doesn't work during build

[juansebastianl]

Contributing guidelines

• I've read the contributing guidelines and wholeheartedly agree

I've found a bug and checked that ...

• ... the documentation does not mention anything about my problem
• ... there are no open or closed issues that are related to my problem

Description

I've got a builder with a custom network with other docker containers attached, during build I have a RUN curl http://my-other-container and I get a Not Found error. The curl works after the container is built and run, as well as in the builder container, but not during the build.

Expected behaviour

I start with a custom network my-network which has my-other-container attached to it.

I create a custom builder

docker buildx create --use \
        --name custom_network_builder \
        --driver docker-container \
        --driver-opt "network=my-network"

and then build my Dockerfile

docker build --builder=custom_network_builder --load -f ./Dockerfile

where my dockerfile is

FROM ubuntu:focal
RUN curl http://my-other-container

then my docker container should build successfully.

Actual behaviour

I get a Could not resolve: my-other-container error from curl and the build fails. I have done docker excec -it buildx_build_container bash and tried the curl and it works as expected. I have also done the curl from the docker container once it is built (after taking the RUN step out) and it works fine as well.

Buildx version

github.com/docker/buildx v0.11.2 9872040

Docker info

No response

Builders list

NAME/NODE DRIVER/ENDPOINT STATUS  BUILDKIT             PLATFORMS
default * docker
  default default         running v0.11.7+d3e6c1360f6e linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/386

Configuration

FROM ubuntu:focal
RUN curl http://my-other-container

docker build --builder=custom_network_builder --load -f ./Dockerfile

Build logs

No response

Additional info

No response

[tonistiigi]

I believe this has been fixed in buildkit v0.13.0 but you need to use --network=host (that effectively means network of your builder container) so that the RUN commands don't use their own (potentially) isolated network.

moby/buildkit#4524