initial-network should not be added to docker build

[turicas]

Description of problem

I added an initial network ("global-net") for a new app and tried to deploy it using git:from-image and it failed:

ERROR: network mode "global-net" not supported by buildkit - you can define a custom network for your builder using the network driver-opt in buildx create

The problem occurs because Dokku calls docker to build the image with the following command:

docker image build \
	--label=dokku \
	--label=org.label-schema.schema-version=1.0 \
	--label=org.label-schema.vendor=dokku \
	--label=com.dokku.image-stage=build \
	--label=com.dokku.builder-type=dockerfile \
	--label=com.dokku.app-name=test-app-1 \
	--label=org.label-schema.schema-version=1.0 \
	--label=org.label-schema.vendor=dokku \
	--label=dokku \
	--network=global-net \
	-t dokku/test-app-1:latest .
# got after executing `dokku git:from-image` with trace on (see below how to reproduce)

... but --network in docker image build does not refer to a Docker network, it expects the networking mode for the RUN instructions during build.
The Docker semantics is not consistent in this case (and it sucks), since in docker run, the --network connects a container to a network (it should be called --networking-mode in docker build image).
I looked for an way to actually attach the network during the build phase and looks like it's not possible, so Dokku should remove the --network=<initial-network>. After some research I think the problem is in this line.

Steps to reproduce

APP_NAME="test-app-1"
NET_NAME="global-net"
APP_IMAGE="nginx:1.27.3-alpine-perl"

# Ensure network exists
sudo docker network rm "$NET_NAME" 2> /dev/null
dokku network:create "$NET_NAME"

# Ensure we have a fresh new app
echo "$APP_NAME" | dokku apps:destroy "$APP_NAME" 2> /dev/null
dokku apps:create "$APP_NAME"

# Set initial network and deploy from image
dokku network:set "$APP_NAME" initial-network "$NET_NAME"
dokku git:from-image "$APP_NAME" "$APP_IMAGE"

# =====> Setting initial-network to global-net
# -----> Generating build context
#        Setting Dockerfile
# -----> Image exists on host, skipping pull
# -----> Updating git repository with specified build context
#        Detected branch, setting deploy-branch to stable
# -----> Cleaning up...
# -----> Building test-app-1 from Dockerfile
# [+] Building 0.0s (0/0)                                                                                                                                      docker:default
# ERROR: network mode "global-net" not supported by buildkit - you can define a custom network for your builder using the network driver-opt in buildx create
#  !     Removing invalid image tag dokku/test-app-1:latest
#  !     App build failed

The same problem will happen if I have a global initial-network set (instead of setting it for the app specifically).

The problem won't happen if I set the initial-network after deploying the image (but only if no global initial-network is set):

APP_NAME="test-app-2"
NET_NAME="global-net"
APP_IMAGE="nginx:1.27.3-alpine-perl"

# Ensure network exists
sudo docker network rm "$NET_NAME" 2> /dev/null
dokku network:create "$NET_NAME"

# Ensure we have a fresh new app
echo "$APP_NAME" | dokku apps:destroy "$APP_NAME" 2> /dev/null
dokku apps:create "$APP_NAME"

# Unset global initial-network, deploy from image, set app network and restart
dokku network:set --global initial-network
dokku git:from-image "$APP_NAME" "$APP_IMAGE"
dokku network:set "$APP_NAME" initial-network "$NET_NAME"
dokku ps:restart "$APP_NAME"

dokku network:report $APP_NAME --format json | jq '."network-initial-network"'
# "global-net"

dokku report $APP_NAME

N/A

Additional information

No response

Output of failing commands after running: dokku trace:off

Output of failing commands after running: dokku trace:on

[josegonzalez]

Probably what we need to do is pass the IMAGE_SOURCE_TYPE (flag.Arg(1)) into network.TriggerDockerArgsProcess() here (and the related places). If the value is dockerfile, do not print out the initial-network. We'd also only want to do this for the build phase, so splitting this out into a separate function is probably best.

[josegonzalez]

Related issue: docker/buildx#175

[josegonzalez]

Correct way to use a network during builds is to use a custom builder it seems. Thats a bit frustrating...

[turicas]

Correct way to use a network during builds is to use a custom builder it seems. Thats a bit frustrating...

So would need to create a builder per app, with its initial networks (global and specific)? Something like docker buildx create --name dokku_builder_app_APPNAME --driver docker-container --driver-opt network=netname

[josegonzalez]

Closing as there is a pull request open.

[turicas]

Thanks!