mirror of https://github.com/k3s-io/k3s
600 lines
22 KiB
Markdown
600 lines
22 KiB
Markdown
k3s - 5 less than k8s
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===============================================
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Lightweight Kubernetes. Easy to install, half the memory, all in a binary less than 40mb.
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Great for
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* Edge
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* IoT
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* CI
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* ARM
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* Situations where a PhD in k8s clusterology is infeasible
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What is this?
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---
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k3s is intended to be a fully compliant Kubernetes distribution with the following changes:
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1. Legacy, alpha, non-default features are removed. Hopefully, you shouldn't notice the
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stuff that has been removed.
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2. Removed most in-tree plugins (cloud providers and storage plugins) which can be replaced
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with out of tree addons.
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3. Add sqlite3 as the default storage mechanism. etcd3 is still available, but not the default.
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4. Wrapped in simple launcher that handles a lot of the complexity of TLS and options.
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5. Minimal to no OS dependencies (just a sane kernel and cgroup mounts needed). k3s packages required
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dependencies
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* containerd
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* Flannel
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* CoreDNS
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* CNI
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* Host utilities (iptables, socat, etc)
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Quick start
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-----------
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1. Download `k3s` from latest [release](https://github.com/rancher/k3s/releases/latest), x86_64, armhf, and arm64 are
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supported
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2. Run server
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```bash
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sudo k3s server &
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# Kubeconfig is written to /etc/rancher/k3s/k3s.yaml
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sudo k3s kubectl get node
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# On a different node run the below. NODE_TOKEN comes from /var/lib/rancher/k3s/server/node-token
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# on your server
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sudo k3s agent --server https://myserver:6443 --token ${NODE_TOKEN}
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```
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Running server
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--------------
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To run the server just do
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k3s server
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You should get an output similar to
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```
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INFO[2019-01-22T15:16:19.908493986-07:00] Starting k3s dev
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INFO[2019-01-22T15:16:19.908934479-07:00] Running kube-apiserver --allow-privileged=true --authorization-mode Node,RBAC --service-account-signing-key-file /var/lib/rancher/k3s/server/tls/service.key --service-cluster-ip-range 10.43.0.0/16 --advertise-port 6445 --advertise-address 127.0.0.1 --insecure-port 0 --secure-port 6444 --bind-address 127.0.0.1 --tls-cert-file /var/lib/rancher/k3s/server/tls/localhost.crt --tls-private-key-file /var/lib/rancher/k3s/server/tls/localhost.key --service-account-key-file /var/lib/rancher/k3s/server/tls/service.key --service-account-issuer k3s --api-audiences unknown --basic-auth-file /var/lib/rancher/k3s/server/cred/passwd --kubelet-client-certificate /var/lib/rancher/k3s/server/tls/token-node.crt --kubelet-client-key /var/lib/rancher/k3s/server/tls/token-node.key
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Flag --insecure-port has been deprecated, This flag will be removed in a future version.
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INFO[2019-01-22T15:16:20.196766005-07:00] Running kube-scheduler --kubeconfig /var/lib/rancher/k3s/server/cred/kubeconfig-system.yaml --port 0 --secure-port 0 --leader-elect=false
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INFO[2019-01-22T15:16:20.196880841-07:00] Running kube-controller-manager --kubeconfig /var/lib/rancher/k3s/server/cred/kubeconfig-system.yaml --service-account-private-key-file /var/lib/rancher/k3s/server/tls/service.key --allocate-node-cidrs --cluster-cidr 10.42.0.0/16 --root-ca-file /var/lib/rancher/k3s/server/tls/token-ca.crt --port 0 --secure-port 0 --leader-elect=false
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Flag --port has been deprecated, see --secure-port instead.
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INFO[2019-01-22T15:16:20.273441984-07:00] Listening on :6443
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INFO[2019-01-22T15:16:20.278383446-07:00] Writing manifest: /var/lib/rancher/k3s/server/manifests/coredns.yaml
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INFO[2019-01-22T15:16:20.474454524-07:00] Node token is available at /var/lib/rancher/k3s/server/node-token
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INFO[2019-01-22T15:16:20.474471391-07:00] To join node to cluster: k3s agent -s https://10.20.0.3:6443 -t ${NODE_TOKEN}
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INFO[2019-01-22T15:16:20.541027133-07:00] Wrote kubeconfig /etc/rancher/k3s/k3s.yaml
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INFO[2019-01-22T15:16:20.541049100-07:00] Run: k3s kubectl
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```
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The output will probably be much longer as the agent will spew a lot of logs. By default the server
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will register itself as a node (run the agent). It is common and almost required these days
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that the control plane be part of the cluster. To not run the agent by default use the `--disable-agent`
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flag
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k3s server --disable-agent
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At this point, you can run the agent as a separate process or not run it on this node at all.
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If you encounter an error like `"stream server error: listen tcp: lookup some-host on X.X.X.X:53: no such host"`
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when starting k3s please ensure `/etc/hosts` contains your current hostname (output of `hostname`),
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set to a 127.x.x.x address. For example:
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```
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127.0.1.1 myhost
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```
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Joining nodes
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-------------
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When the server starts it creates a file `/var/lib/rancher/k3s/server/node-token`. Use the contents
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of that file as `NODE_TOKEN` and then run the agent as follows
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k3s agent --server https://myserver:6443 --token ${NODE_TOKEN}
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That's it.
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Accessing cluster from outside
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-----------------------------
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Copy `/etc/rancher/k3s/k3s.yaml` on your machine located outside the cluster as `~/.kube/config`. Then replace
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"localhost" with the IP or name of your k3s server. `kubectl` can now manage your k3s cluster.
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Auto-deploying manifests
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------------------------
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Any file found in `/var/lib/rancher/k3s/server/manifests` will automatically be deployed to
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Kubernetes in a manner similar to `kubectl apply`.
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It is also possible to deploy Helm charts. k3s supports a CRD controller for installing charts. A YAML file specification can look as following (example taken from `/var/lib/rancher/k3s/server/manifests/traefik.yaml`):
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```yaml
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apiVersion: k3s.cattle.io/v1
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kind: HelmChart
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metadata:
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name: traefik
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namespace: kube-system
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spec:
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chart: stable/traefik
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set:
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rbac.enabled: "true"
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ssl.enabled: "true"
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```
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Keep in mind that `namespace` in your HelmChart resource metadata section should always be `kube-system`, because k3s deploy controller is configured to watch this namespace for new HelmChart resources. If you want to specify the namespace for the actual helm release, you can do that using `targetNamespace` key in the spec section:
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```
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apiVersion: k3s.cattle.io/v1
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kind: HelmChart
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metadata:
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name: grafana
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namespace: kube-system
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spec:
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chart: stable/grafana
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targetNamespace: monitoring
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set:
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adminPassword: "NotVerySafePassword"
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valuesContent: |-
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image:
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tag: master
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env:
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GF_EXPLORE_ENABLED: true
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adminUser: admin
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sidecar:
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datasources:
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enabled: true
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```
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Also note that besides `set` you can use `valuesContent` in the spec section. And it's okay to use both of them.
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Building from source
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--------------------
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The clone will be much faster on this repo if you do
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git clone --depth 1 https://github.com/rancher/k3s.git
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This repo includes all of Kubernetes history so `--depth 1` will avoid most of that.
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For development, you just need go 1.12 and a sane GOPATH. To compile the binaries run
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```bash
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go build -o k3s
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go build -o kubectl ./cmd/kubectl
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go build -o hyperkube ./vendor/k8s.io/kubernetes/cmd/hyperkube
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```
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This will create the main executable, but it does not include the dependencies like containerd, CNI,
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etc. To run a server and agent with all the dependencies for development run the following
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helper scripts
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```bash
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# Server
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./scripts/dev-server.sh
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# Agent
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./scripts/dev-agent.sh
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```
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To build the full release binary run `make` and that will create `./dist/artifacts/k3s`
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Customizing components
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----------------------
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As of v0.3.0 any of the following processes can be customized with extra flags:
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- kube-apiserver (server)
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- kube-controller-manager (server)
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- kube-scheduler (server)
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- kubelet (agent)
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- kube-proxy (agent)
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Adding extra argument can be done by passing the following flags to server or agent:
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```
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--kube-apiserver-arg value
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--kube-scheduler-arg value
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--kube-controller-arg value
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--kubelet-arg value
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--kube-proxy-arg value
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```
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For example to add the following arguments `-v=9` and `log-file=/tmp/kubeapi.log` to the kube-apiserver, you should pass the following:
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```
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k3s server --kube-apiserver-arg v=9 --kube-apiserver-arg log-file=/tmp/kubeapi.log
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```
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Uninstalling server
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-----------------
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If you installed your k3s server with the help of `install.sh` script from the root directory, you may use the uninstall script generated during installation, which will be created on your server node at `/usr/local/bin/k3s-uninstall.sh`
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Kubernetes source
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-----------------
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The source code for Kubernetes is in `vendor/` and the location from which that is copied
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is in `./vendor.conf`. Go to the referenced repo/tag and you'll find all the patches applied
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to upstream Kubernetes.
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Open ports / Network security
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---------------------------
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The server needs port 6443 to be accessible by the nodes. The nodes need to be able to reach
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other nodes over UDP port 8472. This is used for flannel VXLAN. If you don't use flannel
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and provide your own custom CNI, then 8472 is not needed by k3s. The node should not listen
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on any other port. k3s uses reverse tunneling such that the nodes make outbound connections
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to the server and all kubelet traffic runs through that tunnel.
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IMPORTANT. The VXLAN port on nodes should not be exposed to the world, it opens up your
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cluster network to accessed by anyone. Run your nodes behind a firewall/security group that
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disables access to port 8472.
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Server HA
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---------
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Just don't right now :) It's currently broken.
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Running in Docker (and docker-compose)
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-----------------
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I wouldn't be me if I couldn't run my cluster in Docker. `rancher/k3s` images are available
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to run k3s server and agent from Docker. A `docker-compose.yml` is in the root of this repo that
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serves as an example of how to run k3s from Docker. To run from `docker-compose` from this repo run
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docker-compose up --scale node=3
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# kubeconfig is written to current dir
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kubectl --kubeconfig kubeconfig.yaml get node
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NAME STATUS ROLES AGE VERSION
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497278a2d6a2 Ready <none> 11s v1.13.2-k3s2
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d54c8b17c055 Ready <none> 11s v1.13.2-k3s2
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db7a5a5a5bdd Ready <none> 12s v1.13.2-k3s2
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To run the agent only in Docker use the following `docker-compose-agent.yml` is in the root of this repo that
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serves as an example of how to run k3s agent from Docker. Alternatively the Docker run command can also be used;
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sudo docker run -d --tmpfs /run --tmpfs /var/run -e K3S_URL=${SERVER_URL} -e K3S_TOKEN=${NODE_TOKEN} --privileged rancher/k3s:v0.5.0
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sudo docker run -d --tmpfs /run --tmpfs /var/run -e K3S_URL=https://k3s.example.com:6443 -e K3S_TOKEN=K13849a67fc385fd3c0fa6133a8649d9e717b0258b3b09c87ffc33dae362c12d8c0::node:2e373dca319a0525745fd8b3d8120d9c --privileged rancher/k3s:v0.5.0
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Hyperkube
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--------
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k3s is bundled in a nice wrapper to remove the majority of the headache of running k8s. If
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you don't want that wrapper and just want a smaller k8s distro, the releases includes
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the `hyperkube` binary you can use. It's then up to you to know how to use `hyperkube`. If
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you want individual binaries you will need to compile them yourself from source
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containerd and Docker
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----------
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k3s includes and defaults to containerd. Why? Because it's just plain better. If you want to
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run with Docker first stop and think, "Really? Do I really want more headache?" If still
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yes then you just need to run the agent with the `--docker` flag
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k3s agent -s ${SERVER_URL} -t ${NODE_TOKEN} --docker &
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k3s will generate config.toml for containerd in `/var/lib/rancher/k3s/agent/etc/containerd/config.toml`, for advanced customization for this file you can create another file called `config.toml.tmpl` in the same directory and it will be used instead.
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The `config.toml.tmpl` will be treated as a Golang template file, and the `config.Node` structure is being passed to the template,the following is an example on how to use the structure to customize the configuration file https://github.com/rancher/k3s/blob/master/pkg/agent/templates/templates.go#L16-L32
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systemd
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-------
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If you are bound by the shackles of systemd (as most of us are), there is a sample unit file
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in the root of this repo `k3s.service` which is as follows
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```ini
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[Unit]
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Description=Lightweight Kubernetes
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Documentation=https://k3s.io
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After=network-online.target
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[Service]
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Type=notify
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EnvironmentFile=/etc/systemd/system/k3s.service.env
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ExecStart=/usr/local/bin/k3s server
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KillMode=process
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Delegate=yes
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LimitNOFILE=infinity
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LimitNPROC=infinity
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LimitCORE=infinity
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TasksMax=infinity
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TimeoutStartSec=0
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Restart=always
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[Install]
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WantedBy=multi-user.target
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```
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The k3s `install.sh` script also provides a convenient way for installing to systemd,
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to install the agent and server as a k3s service just run:
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```sh
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curl -sfL https://get.k3s.io | sh -
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```
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The install script will attempt to download the latest release, to specify a specific
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version for download we can use the `INSTALL_K3S_VERSION` environment variable, eg:
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```sh
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curl -sfL https://get.k3s.io | INSTALL_K3S_VERSION=vX.Y.Z-rc1 sh -
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```
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To install just the server without an agent we can add a `INSTALL_K3S_EXEC`
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environment variable to the command:
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```sh
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curl -sfL https://get.k3s.io | INSTALL_K3S_EXEC="--disable-agent" sh -
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```
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To install just the agent without a server we should pass `K3S_URL` along with
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`K3S_TOKEN` or `K3S_CLUSTER_SECRET`, eg:
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```sh
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curl -sfL https://get.k3s.io | K3S_URL=https://example-url:6443 K3S_TOKEN=XXX sh -
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```
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The installer can also be run without performing downloads by setting `INSTALL_K3S_SKIP_DOWNLOAD=true`, eg:
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```sh
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curl -sfL https://github.com/rancher/k3s/releases/download/vX.Y.Z/k3s -o /usr/local/bin/k3s
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chmod 0755 /usr/local/bin/k3s
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curl -sfL https://get.k3s.io -o install-k3s.sh
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chmod 0755 install-k3s.sh
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export INSTALL_K3S_SKIP_DOWNLOAD=true
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./install-k3s.sh
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```
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The full help text for the install script environment variables are as follows:
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- `K3S_*`
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Environment variables which begin with `K3S_` will be preserved for the
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systemd service to use. Setting `K3S_URL` without explicitly setting
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a systemd exec command will default the command to "agent", and we
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enforce that `K3S_TOKEN` or `K3S_CLUSTER_SECRET` is also set.
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- `INSTALL_K3S_SKIP_DOWNLOAD`
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If set to true will not download k3s hash or binary.
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- `INSTALL_K3S_VERSION`
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Version of k3s to download from github. Will attempt to download the
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latest version if not specified.
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- `INSTALL_K3S_BIN_DIR`
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Directory to install k3s binary, links, and uninstall script to, or use
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/usr/local/bin as the default
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- `INSTALL_K3S_SYSTEMD_DIR`
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Directory to install systemd service and environment files to, or use
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/etc/systemd/system as the default
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- `INSTALL_K3S_EXEC` or script arguments
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Command with flags to use for launching k3s in the systemd service, if
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the command is not specified will default to "agent" if `K3S_URL` is set
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or "server" if not. The final systemd command resolves to a combination
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of EXEC and script args ($@).
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The following commands result in the same behavior:
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```sh
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curl ... | INSTALL_K3S_EXEC="--disable-agent" sh -s -
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curl ... | INSTALL_K3S_EXEC="server --disable-agent" sh -s -
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curl ... | INSTALL_K3S_EXEC="server" sh -s - --disable-agent
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curl ... | sh -s - server --disable-agent
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curl ... | sh -s - --disable-agent
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```
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- `INSTALL_K3S_NAME`
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Name of systemd service to create, will default from the k3s exec command
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if not specified. If specified the name will be prefixed with 'k3s-'.
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- `INSTALL_K3S_TYPE`
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Type of systemd service to create, will default from the k3s exec command
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if not specified.
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openrc on Alpine Linux
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-------
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In order to pre-setup Alpine Linux you have to go through the following steps:
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```bash
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echo "cgroup /sys/fs/cgroup cgroup defaults 0 0" >> /etc/fstab
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cat >> /etc/cgconfig.conf <<EOF
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mount {
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cpuacct = /cgroup/cpuacct;
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memory = /cgroup/memory;
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devices = /cgroup/devices;
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freezer = /cgroup/freezer;
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net_cls = /cgroup/net_cls;
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blkio = /cgroup/blkio;
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cpuset = /cgroup/cpuset;
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cpu = /cgroup/cpu;
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}
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EOF
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```
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Then update **/etc/update-extlinux.conf** by adding:
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```
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default_kernel_opts="... cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory"
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```
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Than update the config and reboot
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```bash
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update-extlinux
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reboot
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```
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After rebooting:
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- download **k3s** to **/usr/local/bin/k3s**
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- create an openrc file in **/etc/init.d**
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For the server:
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```bash
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#!/sbin/openrc-run
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command=/usr/local/bin/k3s
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command_args="server"
|
|
pidfile=
|
|
|
|
name="k3s"
|
|
description="Lightweight Kubernetes"
|
|
```
|
|
|
|
For the agent:
|
|
|
|
```bash
|
|
#!/sbin/openrc-run
|
|
|
|
command=/usr/local/bin/k3s
|
|
command_args="agent --server https://myserver:6443 --token ${NODE_TOKEN}"
|
|
pidfile=
|
|
|
|
name="k3s"
|
|
description="Lightweight Kubernetes"
|
|
```
|
|
|
|
Flannel
|
|
-------
|
|
|
|
Flannel is included by default, if you don't want flannel then run the agent with `--no-flannel` as follows
|
|
|
|
k3s agent -u ${SERVER_URL} -t ${NODE_TOKEN} --no-flannel &
|
|
|
|
In this setup you will still be required to install your own CNI driver. More info [here](https://kubernetes.io/docs/setup/independent/create-cluster-kubeadm/#pod-network)
|
|
|
|
CoreDNS
|
|
-------
|
|
|
|
CoreDNS is deployed on start of the agent, to disable add `--no-deploy coredns` to the server
|
|
|
|
k3s server --no-deploy coredns
|
|
|
|
If you don't install CoreDNS you will need to install a cluster DNS provider yourself.
|
|
|
|
Traefik
|
|
-------
|
|
|
|
Traefik is deployed by default when starting the server; to disable it, start the server with `--no-deploy traefik` like this
|
|
|
|
k3s server --no-deploy traefik
|
|
|
|
Service load balancer
|
|
---------------------
|
|
|
|
k3s includes a basic service load balancer that uses available host ports. If you try to create
|
|
a load balancer that listens on port 80, for example, it will try to find a free host in the cluster
|
|
for port 80. If no port is available the load balancer will stay in Pending.
|
|
|
|
To disable the embedded service load balancer (if you wish to use a different implementation like
|
|
MetalLB) just add `--no-deploy=servicelb` to the server on startup.
|
|
|
|
Air-Gap Support
|
|
---------------
|
|
|
|
k3s supports pre-loading of containerd images by placing them in the `images` directory for the agent before starting, eg:
|
|
```sh
|
|
sudo mkdir -p /var/lib/rancher/k3s/agent/images/
|
|
sudo cp ./k3s-airgap-images-$ARCH.tar /var/lib/rancher/k3s/agent/images/
|
|
```
|
|
Images needed for a base install are provided through the releases page, additional images can be created with the `docker save` command.
|
|
|
|
Offline Helm charts are served from the `/var/lib/rancher/k3s/server/static` directory, and Helm chart manifests may reference the static files with a `%{KUBERNETES_API}%` templated variable. For example, the default traefik manifest chart installs from `https://%{KUBERNETES_API}%/static/charts/traefik-X.Y.Z.tgz`.
|
|
|
|
If networking is completely disabled k3s may not be able to start (ie ethernet unplugged or wifi disconnected), in which case it may be necessary to add a default route. For example:
|
|
```sh
|
|
sudo ip -c address add 192.168.123.123/24 dev eno1
|
|
sudo ip route add default via 192.168.123.1
|
|
```
|
|
|
|
k3s additionally provides a `--resolv-conf` flag for kubelets, which may help with configuring DNS in air-gap networks.
|
|
|
|
Rootless - (Some advanced magic, user beware)
|
|
--------
|
|
|
|
Initial rootless support has been added but there are a series of significant usability issues surrounding it.
|
|
We are releasing the initial support for those interested in rootless and hopefully some people can help to
|
|
improve the usability. First ensure you have proper setup and support for user namespaces. Refer to the
|
|
[requirements section](https://github.com/rootless-containers/rootlesskit#setup) in rootlesskit for instructions.
|
|
In short, latest Ubuntu is your best bet for this to work.
|
|
|
|
Node Labels and Taints
|
|
----------------------
|
|
|
|
k3s server and agent can be configured with options `--node-label` and `--node-taint` which adds set of Labels and Taints to kubelet, the two options only adds labels/taints at registration time, so they can only be added once and not changed after that, an example to add new label is:
|
|
```
|
|
k3s server --node-label foo=bar --node-label hello=world --node-taint key1=value1:NoExecute
|
|
```
|
|
|
|
## Issues w/ Rootless
|
|
|
|
When running rootless a new network namespace is created. This means that k3s instance is running with networking
|
|
fairly detached from the host. The only way to access services run in k3s from the host is to setup port forwards
|
|
to the k3s network namespace. We have a controller that will automatically bind 6443 and any service port to the
|
|
host with an offset of 10000. That means service port 80 will become 10080 on the host. Once you kill k3s and then
|
|
start a new instance of k3s it will create a new network namespace, but it doesn't kill the old pods. So you are left
|
|
with a fairly broken setup. This is the main issue at the moment, how to deal with the network namespace.
|
|
|
|
## Running w/ Rootless
|
|
|
|
Just add `--rootless` flag to either server or agent. So run `k3s server --rootless` and then look for the message
|
|
`Wrote kubeconfig [SOME PATH]` for where your kubeconfig to access you cluster is. Becareful, if you use `-o` to write
|
|
the kubeconfig to a different directory it will probably not work. This is because the k3s instance in running in a different
|
|
mount namespace.
|
|
|
|
## Upgrades
|
|
|
|
To upgrade k3s from an older version you can re-run the installation script using the same flags, eg:
|
|
|
|
```sh
|
|
curl -sfL https://get.k3s.io | sh -
|
|
```
|
|
|
|
If you want to upgrade to specific version you can run the following command:
|
|
|
|
```sh
|
|
curl -sfL https://get.k3s.io | INSTALL_K3S_VERSION=vX.Y.Z-rc1 sh -
|
|
```
|
|
|
|
Or to manually upgrade k3s:
|
|
1. Download the desired version of k3s from [releases](https://github.com/rancher/k3s/releases/latest)
|
|
2. Install to an appropriate location (normally `/usr/local/bin/k3s`)
|
|
3. Stop the old version
|
|
4. Start the new version
|
|
|
|
Restarting k3s is supported by the installation script for systemd and openrc.
|
|
To restart manually for systemd use:
|
|
```sh
|
|
sudo systemctl restart k3s
|
|
```
|
|
|
|
To restart manually for openrc use:
|
|
```sh
|
|
sudo service k3s restart
|
|
```
|
|
|
|
Upgrading an air-gap environment can be accomplished in the following manner:
|
|
1. Download air-gap images and install if changed
|
|
2. Install new k3s binary (from installer or manual download)
|
|
3. Restart k3s (if not restarted automatically by installer)
|
|
|
|
TODO
|
|
----
|
|
Currently broken or stuff that needs to be done for this to be considered production quality.
|
|
|
|
1. Metrics API ([fixed](https://github.com/rancher/k3s/issues/252): use `k3s server --kubelet-arg="address=0.0.0.0"` and apply `recipes/metrics-server`)
|
|
2. HA
|
|
3. Work on e2e, sonobouy.
|
|
4. etcd doesn't actually work because args aren't exposed
|