This repository contains the information required to build the smarter-dns image that can be used to provide Pod discovery via DNS in a SMARTER cluster.
Smarter-dns is deployed using a Kubernetes DaemonSet - a smarter-dns Pod is created on every node with the relevant label and provides DNS lookup including Pod discovery.
Different nodes may be using different Container Runtimes and the smarter.cri label is used to distinguish between them. At least one of these labels must be present on the node for smarter-dns to be deployed to it.
Apply label smarter.cri=docker when using docker
Apply label smarter.cri=containerd when using containerd
Note that when using docker as the container runtime it is necessary to use the SMARTER k3s agent on the node
A helm chart available at the the chart directory can be used to install smarter-dns
helm install smarter-dns chart
Three YAML files are provided for smarter-dns depending on the container runtime that is being used on the node.
| YAML | Usage |
|---|---|
smarterdns_ds_docker.yaml |
Use this when using k3s with docker as the container runtime |
smarterdns_ds_containerd.yaml |
Use this when using k3s with an external containerd |
smarterdns_ds_k3s_containerd.yaml |
Use this when using k3s with it's bundled containerd |
See https://github.com/smarter-project/smarter-dns for the latest release of these YAML files.
The smarterdnsconfig ConfigMap can be used to customise the smarterdns deployment.
When the k3s server is started, the following arguments must be provided to enable smarter-dns to function correctly:
`--no-deploy coredns --cluster-dns "169.254.0.2"
The --cluster-dns argument enables k3s to setup each Pod to point to the smarter-dns Pod for name resolution.
Alternatively this flag can be provided to the k3s agent running on each node via the --kubelet-arg flag:
`--kubelet-arg cluster-dns=169.254.0.2`
Which ever method is used, the value must match that specified by the CLUSTER_DNS key/value in the smarterdnsconfig configmap (see the smarterdns_ds_docker.yaml file)
smarter-dns uses the k3s crictl command and assumes that the k3s binary can be found at /usr/bin/k3s. This location can be configured by setting the CRICTL_BIN value in the smarterdnsconfig configmap in the smarter-dns YAML file.
The CRI_DIR entry in the smarterdnsconfig configmap can be used to point to the directory containing the socket file for the container runtime.
The CRI_FILE entry in the smarterdnsconfig configmap should then be set to the name of the socket file within the CRI_DIR directory.
Deploy the daemonset using:
k3s kubectl apply -f smarterdns_ds_docker.yaml
DNS queries from normal pods and pods with host networking will all go to the IP address specified as the cluster-dns IP (by default this is 169.254.0.2)
The smarterdns pod sets up iptable rules to redirect these queries to the actual smarter-dns server which is executing as a pod with host-networking.
Discovery of pod IPs on the node can also be performed by querying the same address: 169.254.0.2
To build the smarter-dns image using docker:
docker buildx create --use --name mybuild
docker buildx build --platform linux/arm64/v8,linux/arm/v7,linux/amd64 -t ghcr.io/smarter-project/smarter-dns:vX.Y.Z --push .
You can replace "ghcr.io/smarter-project/smarter-dns" with your own registry and then adjust the YAML file accordingly.