In this guide we will create a Talos cluster running in an air-gapped environment with all the required images being pulled from an internal registry. We will use the QEMU provisioner available in talosctl to create a local cluster, but the same approach could be used to deploy Talos in bigger air-gapped networks.

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Requirements

The follow are requirements for this guide:
  • Docker 18.03 or greater
  • Requirements for the Talos QEMU cluster

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Identifying Images

In air-gapped environments, access to the public Internet is restricted, so Talos can’t pull images from public Docker registries (docker.io, ghcr.io, etc.) We need to identify the images required to install and run Talos. The same strategy can be used for images required by custom workloads running on the cluster. The talosctl image default command provides a list of default images used by the Talos cluster (with default configuration settings). To print the list of images, run: 
talosctl image default
This list contains images required by a default deployment of Talos. There might be additional images required for the workloads running on this cluster, and those should be added to this list.

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Preparing the Internal Registry

As access to the public registries is restricted, we have to run an internal Docker registry. In this guide, we will launch the registry on the same machine using Docker: 
$ docker run -d -p 6000:5000 --restart always --name registry-airgapped registry:2
1bf09802bee1476bc463d972c686f90a64640d87dacce1ac8485585de69c91a5
This registry will be accepting connections on port 6000 on the host IPs. The registry is empty by default, so we have fill it with the images required by Talos. First, we pull all the images to our local Docker daemon: 
$ for image in `talosctl image default`; do docker pull $image; done
v0.15.1: Pulling from coreos/flannel
Digest: sha256:9a296fbb67790659adc3701e287adde3c59803b7fcefe354f1fc482840cdb3d9
...
All images are now stored in the Docker daemon store: 
$ docker images
REPOSITORY                               TAG                                        IMAGE ID       CREATED         SIZE
gcr.io/etcd-development/etcd             v3.5.3                                     604d4f022632   6 days ago      181MB
ghcr.io/siderolabs/install-cni           v1.0.0-2-gc5d3ab0                          4729e54f794d   6 days ago      76MB
...
Now we need to re-tag them so that we can push them to our local registry. We are going to replace the first component of the image name (before the first slash) with our registry endpoint 127.0.0.1:6000: 
$ for image in `talosctl image default`; do \
    docker tag $image `echo $image | sed -E 's#^[^/]+/#127.0.0.1:6000/#'`; \
  done
As the next step, we push images to the internal registry: 
$ for image in `talosctl image default`; do \
    docker push `echo $image | sed -E 's#^[^/]+/#127.0.0.1:6000/#'`; \
  done
We can now verify that the images are pushed to the registry: 
$ curl http://127.0.0.1:6000/v2/_catalog
{"repositories":["coredns/coredns","coreos/flannel","etcd-development/etcd","kube-apiserver","kube-controller-manager","kube-proxy","kube-scheduler","pause","siderolabs/install-cni","siderolabs/installer","siderolabs/kubelet"]}
Note: images in the registry don’t have the registry endpoint prefix anymore.

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Launching Talos in an Air-gapped Environment

For Talos to use the internal registry, we use the registry mirror feature to redirect all image pull requests to the internal registry. This means that the registry endpoint (as the first component of the image reference) gets ignored, and all pull requests are sent directly to the specified endpoint. We are going to use a QEMU-based Talos cluster for this guide, but the same approach works with Docker-based clusters as well. As QEMU-based clusters go through the Talos install process, they can be used better to model a real air-gapped environment. Identify all registry prefixes from talosctl image default, for example:
  • docker.io
  • gcr.io
  • ghcr.io
  • registry.k8s.io
The talosctl cluster create command provides conveniences for common configuration options. The only required flag for this guide is --registry-mirror <endpoint>=http://10.5.0.1:6000 which redirects every pull request to the internal registry, this flag needs to be repeated for each of the identified registry prefixes above. The endpoint being used is 10.5.0.1, as this is the default bridge interface address which will be routable from the QEMU VMs (127.0.0.1 IP will be pointing to the VM itself).
Note: --install-image should match the image which was copied into the internal registry in the previous step.
You can be verify that the cluster is air-gapped by inspecting the registry logs: docker logs -f registry-airgapped.

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Closing Notes

Running in an air-gapped environment might require additional configuration changes, for example using custom settings for DNS and NTP servers. When scaling this guide to the bare-metal environment, following Talos config snippet could be used as an equivalent of the --registry-mirror flag above: 
machine:
  ...
  registries:
      mirrors:
        docker.io:
          endpoints:
          - http://10.5.0.1:6000/
        gcr.io:
          endpoints:
          - http://10.5.0.1:6000/
        ghcr.io:
          endpoints:
          - http://10.5.0.1:6000/
        registry.k8s.io:
          endpoints:
          - http://10.5.0.1:6000/
...
Other implementations of Docker registry can be used in place of the Docker registry image used above to run the registry. If required, auth can be configured for the internal registry (and custom TLS certificates if needed). Please see pull-through cache guide for an example using Harbor container registry with Talos.