Remote driver

Estimated reading time: 5 minutes

The buildx remote driver allows for more complex custom build workloads that allow users to connect to external buildkit instances. This is useful for scenarios that require manual management of the buildkit daemon, or where a buildkit daemon is exposed from another source.

To connect to a running buildkitd instance:

$ docker buildx create \
  --name remote \
  --driver remote \
  tcp://localhost:1234

Remote Buildkit over Unix sockets

In this scenario, we’ll create a setup with buildkitd listening on a unix socket, and have buildx connect through it.

Firstly, ensure that buildkit is installed. For example, you can launch an instance of buildkitd with:

$ sudo ./buildkitd --group $(id -gn) --addr unix://$HOME/buildkitd.sock

Alternatively, see here for running buildkitd in rootless mode or here for examples of running it as a systemd service.

You should now have a unix socket accessible to your user, that is available to connect to:

$ ls -lh /home/user/buildkitd.sock
srw-rw---- 1 root user 0 May  5 11:04 /home/user/buildkitd.sock

You can then connect buildx to it with the remote driver:

$ docker buildx create \
  --name remote-unix \
  --driver remote \
  unix://$HOME/buildkitd.sock

If you list available builders, you should then see remote-unix among them:

$ docker buildx ls
NAME/NODE           DRIVER/ENDPOINT                        STATUS  PLATFORMS
remote-unix         remote
  remote-unix0      unix:///home/.../buildkitd.sock        running linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/386
default *           docker
  default           default                                running linux/amd64, linux/386

We can switch to this new builder as the default using docker buildx use remote-unix, or specify it per build:

$ docker buildx build --builder=remote-unix -t test --load .

(remember that --load is necessary when not using the default docker driver, to load the build result into the docker daemon)

Remote Buildkit in Docker container

In this scenario, we’ll create a similar setup to the docker-container driver, by manually booting a buildkit docker container and connecting to it using the buildx remote driver. In most cases you’d probably just use the docker-container driver that connects to buildkit through the Docker daemon, but in this case we manually create a container and access it via it’s exposed port.

First, we need to generate certificates for buildkit - you can use the create-certs.sh script as a starting point. Note, that while it is possible to expose buildkit over TCP without using TLS, it is not recommended, since this will allow arbitrary access to buildkit without credentials.

With our certificates generated in .certs/, we startup the container:

$ docker run -d --rm \
  --name=remote-buildkitd \
  --privileged \
  -p 1234:1234 \
  -v $PWD/.certs:/etc/buildkit/certs \
  moby/buildkit:latest \
  --addr tcp://0.0.0.0:1234 \
  --tlscacert /etc/buildkit/certs/ca.pem \
  --tlscert /etc/buildkit/certs/daemon-cert.pem \
  --tlskey /etc/buildkit/certs/daemon-key.pem

The above command starts a buildkit container and exposes the daemon’s port 1234 to localhost.

We can now connect to this running container using buildx:

$ docker buildx create \
  --name remote-container \
  --driver remote \
  --driver-opt cacert=.certs/ca.pem,cert=.certs/client-cert.pem,key=.certs/client-key.pem,servername=... \
  tcp://localhost:1234

Alternatively, we could use the docker-container:// URL scheme to connect to the buildkit container without specifying a port:

$ docker buildx create \
  --name remote-container \
  --driver remote \
  docker-container://remote-container

Remote Buildkit in Kubernetes

In this scenario, we’ll create a similar setup to the kubernetes driver by manually creating a buildkit Deployment. While the kubernetes driver will do this under-the-hood, it might sometimes be desirable to scale buildkit manually. Additionally, when executing builds from inside Kubernetes pods, the buildx builder will need to be recreated from within each pod or copied between them.

Firstly, we can create a kubernetes deployment of buildkitd, as per the instructions here. Following the guide, we setup certificates for the buildkit daemon and client (as above using create-certs.sh) and create a Deployment of buildkit pods with a service that connects to them.

Assuming that the service is called buildkitd, we can create a remote builder in buildx, ensuring that the listed certificate files are present:

$ docker buildx create \
  --name remote-kubernetes \
  --driver remote \
  --driver-opt cacert=.certs/ca.pem,cert=.certs/client-cert.pem,key=.certs/client-key.pem \
  tcp://buildkitd.default.svc:1234

Note that the above will only work in-cluster (since the buildkit setup guide only creates a ClusterIP service). To configure the builder to be accessible remotely, you can use an appropriately configured Ingress, which is outside the scope of this guide.

To access the service remotely, we can use the port forwarding mechanism in kubectl:

$ kubectl port-forward svc/buildkitd 1234:1234

Then you can simply point the remote driver at tcp://localhost:1234.

Alternatively, we could use the kube-pod:// URL scheme to connect directly to a buildkit pod through the kubernetes api (note that this method will only connect to a single pod in the deployment):

$ kubectl get pods --selector=app=buildkitd -o json | jq -r '.items[].metadata.name
buildkitd-XXXXXXXXXX-xxxxx
$ docker buildx create \
  --name remote-container \
  --driver remote \
  kube-pod://buildkitd-XXXXXXXXXX-xxxxx
build, buildx, driver, builder, remote