k3s - 5 less than k8s

Lightweight Kubernetes. Easy to install, half the memory, all in a binary less than 40mb.

Great for

• Edge
• IoT
• CI
• ARM
• Situations where a PhD in k8s clusterology is infeasible

What is this?

k3s is intended to be a fully compliant Kubernetes distribution with the following changes:

1. Legacy, alpha, non-default features are removed. Hopefully, you shouldn't notice the stuff that has been removed.
2. Removed most in-tree plugins (cloud providers and storage plugins) which can be replaced with out of tree addons.
3. Add sqlite3 as the default storage mechanism. etcd3 is still available, but not the default.
4. Wrapped in simple launcher that handles a lot of the complexity of TLS and options.
5. Minimal to no OS dependencies (just a sane kernel and cgroup mounts needed). k3s packages required dependencies
   • containerd
   • Flannel
   • CoreDNS
   • CNI
   • Host utilities (iptables, socat, etc)

Quick start

1. Download k3s from latest release, x86_64, armhf, and arm64 are supported
2. Run server

sudo k3s server &
# Kubeconfig is written to /etc/rancher/k3s/k3s.yaml
sudo k3s kubectl get node

# On a different node run the below. NODE_TOKEN comes from /var/lib/rancher/k3s/server/node-token
# on your server
sudo k3s agent --server https://myserver:6443 --token ${NODE_TOKEN}

Running server

To run the server just do

k3s server

You should get an output similar to

INFO[2019-01-22T15:16:19.908493986-07:00] Starting k3s dev
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
Flag --insecure-port has been deprecated, This flag will be removed in a future version.
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
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
Flag --port has been deprecated, see --secure-port instead.
INFO[2019-01-22T15:16:20.273441984-07:00] Listening on :6443
INFO[2019-01-22T15:16:20.278383446-07:00] Writing manifest: /var/lib/rancher/k3s/server/manifests/coredns.yaml
INFO[2019-01-22T15:16:20.474454524-07:00] Node token is available at /var/lib/rancher/k3s/server/node-token
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}
INFO[2019-01-22T15:16:20.541027133-07:00] Wrote kubeconfig /etc/rancher/k3s/k3s.yaml
INFO[2019-01-22T15:16:20.541049100-07:00] Run: k3s kubectl

The output will probably be much longer as the agent will spew a lot of logs. By default the server will register itself as a node (run the agent). It is common and almost required these days that the control plane be part of the cluster. To not run the agent by default use the --disable-agent flag

k3s server --disable-agent

At this point, you can run the agent as a separate process or not run it on this node at all.

If you encounter an error like "stream server error: listen tcp: lookup some-host on X.X.X.X:53: no such host" when starting k3s please ensure /etc/hosts contains your current hostname (output of hostname), set to a 127.x.x.x address. For example:

127.0.1.1	myhost

Joining nodes

When the server starts it creates a file /var/lib/rancher/k3s/server/node-token. Use the contents of that file as NODE_TOKEN and then run the agent as follows

k3s agent --server https://myserver:6443 --token ${NODE_TOKEN}

That's it.

Accessing cluster from outside

Copy /etc/rancher/k3s/k3s.yaml on your machine located outside the cluster as ~/.kube/config. Then replace "localhost" with the IP or name of your k3s server. kubectl can now manage your k3s cluster.

Auto-deploying manifests

Any file found in /var/lib/rancher/k3s/server/manifests will automatically be deployed to Kubernetes in a manner similar to kubectl apply.

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):

apiVersion: helm.cattle.io/v1
kind: HelmChart
metadata:
  name: traefik
  namespace: kube-system
spec:
  chart: stable/traefik
  set:
    rbac.enabled: "true"
    ssl.enabled: "true"

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:

apiVersion: helm.cattle.io/v1
kind: HelmChart
metadata:
  name: grafana
  namespace: kube-system
spec:
  chart: stable/grafana
  targetNamespace: monitoring
  set:
    adminPassword: "NotVerySafePassword"
  valuesContent: |-
    image:
      tag: master
    env:
      GF_EXPLORE_ENABLED: true
    adminUser: admin
    sidecar:
      datasources:
        enabled: true

Also note that besides set you can use valuesContent in the spec section. And it's okay to use both of them.

k3s versions <= v0.5.0 used k3s.cattle.io for the api group of helmcharts, this has been changed to helm.cattle.io for later versions.

Storage Backends

As of version 0.6.0, k3s can support various storage backends including: SQLite (default), MySQL, Postgres, and etcd, this enahancement depends on the following arguments that can be passed to k3s server:

--storage-backend value             Specify storage type etcd3 or kvsql [$K3S_STORAGE_BACKEND]
--storage-endpoint value            Specify etcd, Mysql, Postgres, or Sqlite (default) data source name [$K3S_STORAGE_ENDPOINT]
--storage-cafile value              SSL Certificate Authority file used to secure storage backend communication [$K3S_STORAGE_CAFILE]
--storage-certfile value            SSL certification file used to secure storage backend communication [$K3S_STORAGE_CERTFILE]
--storage-keyfile value             SSL key file used to secure storage backend communication [$K3S_STORAGE_KEYFILE]

MySQL

To use k3s with MySQL storage backend, you can specify the following for insecure connection:

k3s server --storage-endpoint="mysql://"

By default the server will attempt to connect to mysql using the mysql socket at /var/run/mysqld/mysqld.sock using the root user and with no password, k3s will also create a database with the name kubernetes if the database is not specified in the DSN.

To override the method of connection, user/pass, and database name, you can provide a custom DSN, for example:

k3s server --storage-endpoint="mysql://k3suser:k3spass@tcp(192.168.1.100:3306)/k3stest"

This command will attempt to connect to MySQL on host 192.168.1.100 on port 3306 with username k3suser and password k3spass and k3s will automatically create a new database with the name k3stest if it doesn't exist, for more information about the MySQL driver data source name, please refer to https://github.com/go-sql-driver/mysql#dsn-data-source-name

To connect to MySQL securely, you can use the following example:

k3s server --storage-endpoint="mysql://k3suser:k3spass@tcp(192.168.1.100:3306)/k3stest" --storage-cafile ca.crt --storage-certfile mysql.crt --storage-keyfile mysql.key

The above command will use these certificates to generate the tls config to communicate with mysql securely.

Postgres

Connection to postgres can be established using the following command:

k3s server --storage-endpoint="postgres://"

By default the server will attempt to connect to postgres on localhost with using the postgres user and with postgres password, k3s will also create a database with the name kubernetes if the database is not specified in the DSN.

To override the method of connection, user/pass, and database name, you can provide a custom DSN, for example:

k3s server --storage-endpoint="postgres://k3suser:k3spass@192.168.1.100:5432/k3stest"

This command will attempt to connect to Postgres on host 192.168.1.100 on port 5432 with username k3suser and password k3spass and k3s will automatically create a new database with the name k3stest if it doesn't exist, for more information about the Postgres driver data source name, please refer to https://godoc.org/github.com/lib/pq

To connect to Postgres securely, you can use the following example:

k3s server --storage-endpoint="postgres://k3suser:k3spass@192.168.1.100:5432/k3stest?sslmode=verify-full" --storage-certfile postgres.crt --storage-keyfile postgres.key --storage-cafile ca.crt

The above command will use these certificates to generate the tls config to communicate with postgres securely, note that the sslmode in the example is verify-full which verify that the certification presented by the server was signed by a trusted CA and the server host name matches the one in the certificate.

etcd

Connection to postgres can be established using the following command:

k3s server --storage-backend=etcd3 --storage-endpoint="https://127.0.0.1:2379"

The above command will attempt to connect insecurely to etcd on localhost with port 2379, you can connect securely to etcd using the following command:

k3s server --storage-backend=etcd3 --storage-endpoint="https://127.0.0.1:2379" --storage-cafile ca.crt --storage-certfile etcd.crt --storage-keyfile etcd.key

Building from source

The clone will be much faster on this repo if you do

git clone --depth 1 https://github.com/rancher/k3s.git

This repo includes all of Kubernetes history so --depth 1 will avoid most of that.

For development, you just need go 1.12 and a sane GOPATH. To compile the binaries run

go build -o k3s
go build -o kubectl ./cmd/kubectl
go build -o hyperkube ./vendor/k8s.io/kubernetes/cmd/hyperkube

This will create the main executable, but it does not include the dependencies like containerd, CNI, etc. To run a server and agent with all the dependencies for development run the following helper scripts

# Server
./scripts/dev-server.sh

# Agent
./scripts/dev-agent.sh

To build the full release binary run make and that will create ./dist/artifacts/k3s

Customizing components

As of v0.3.0 any of the following processes can be customized with extra flags:

• kube-apiserver (server)
• kube-controller-manager (server)
• kube-scheduler (server)
• kubelet (agent)
• kube-proxy (agent)

Adding extra argument can be done by passing the following flags to server or agent:

--kube-apiserver-arg value
--kube-scheduler-arg value
--kube-controller-arg value
--kubelet-arg value        
--kube-proxy-arg value     

For example to add the following arguments -v=9 and log-file=/tmp/kubeapi.log to the kube-apiserver, you should pass the following:

k3s server --kube-apiserver-arg v=9 --kube-apiserver-arg log-file=/tmp/kubeapi.log

Uninstalling server

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

Kubernetes source

The source code for Kubernetes is in vendor/ and the location from which that is copied is in ./vendor.conf. Go to the referenced repo/tag and you'll find all the patches applied to upstream Kubernetes.

Open ports / Network security

The server needs port 6443 to be accessible by the nodes. The nodes need to be able to reach other nodes over UDP port 8472. This is used for flannel VXLAN. If you don't use flannel and provide your own custom CNI, then 8472 is not needed by k3s. The node should not listen on any other port. k3s uses reverse tunneling such that the nodes make outbound connections to the server and all kubelet traffic runs through that tunnel.

IMPORTANT. The VXLAN port on nodes should not be exposed to the world, it opens up your cluster network to accessed by anyone. Run your nodes behind a firewall/security group that disables access to port 8472.

Server HA

Just don't right now :) It's currently broken.

Running in Docker (and docker-compose)

I wouldn't be me if I couldn't run my cluster in Docker. rancher/k3s images are available to run k3s server and agent from Docker. A docker-compose.yml is in the root of this repo that serves as an example of how to run k3s from Docker. To run from docker-compose from this repo run

docker-compose up --scale node=3
# kubeconfig is written to current dir
kubectl --kubeconfig kubeconfig.yaml get node

NAME           STATUS   ROLES    AGE   VERSION
497278a2d6a2   Ready    <none>   11s   v1.13.2-k3s2
d54c8b17c055   Ready    <none>   11s   v1.13.2-k3s2
db7a5a5a5bdd   Ready    <none>   12s   v1.13.2-k3s2

To run the agent only in Docker use the following docker-compose-agent.yml is in the root of this repo that serves as an example of how to run k3s agent from Docker. Alternatively the Docker run command can also be used;

sudo docker run -d --tmpfs /run --tmpfs /var/run -e K3S_URL=${SERVER_URL} -e K3S_TOKEN=${NODE_TOKEN} --privileged rancher/k3s:v0.6.0

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:v0.6.0

Hyperkube

k3s is bundled in a nice wrapper to remove the majority of the headache of running k8s. If you don't want that wrapper and just want a smaller k8s distro, the releases includes the hyperkube binary you can use. It's then up to you to know how to use hyperkube. If you want individual binaries you will need to compile them yourself from source

containerd and Docker

k3s includes and defaults to containerd. Why? Because it's just plain better. If you want to run with Docker first stop and think, "Really? Do I really want more headache?" If still yes then you just need to run the agent with the --docker flag

 k3s agent -s ${SERVER_URL} -t ${NODE_TOKEN} --docker &

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.

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

systemd

If you are bound by the shackles of systemd (as most of us are), there is a sample unit file in the root of this repo k3s.service which is as follows

[Unit]
Description=Lightweight Kubernetes
Documentation=https://k3s.io
After=network-online.target

[Service]
Type=notify
EnvironmentFile=/etc/systemd/system/k3s.service.env
ExecStart=/usr/local/bin/k3s server
KillMode=process
Delegate=yes
LimitNOFILE=infinity
LimitNPROC=infinity
LimitCORE=infinity
TasksMax=infinity
TimeoutStartSec=0
Restart=always

[Install]
WantedBy=multi-user.target

The k3s install.sh script also provides a convenient way for installing to systemd, to install the agent and server as a k3s service just run:

curl -sfL https://get.k3s.io | sh -

The install script will attempt to download the latest release, to specify a specific version for download we can use the INSTALL_K3S_VERSION environment variable, eg:

curl -sfL https://get.k3s.io | INSTALL_K3S_VERSION=vX.Y.Z-rc1 sh -

To install just the server without an agent we can add a INSTALL_K3S_EXEC environment variable to the command:

curl -sfL https://get.k3s.io | INSTALL_K3S_EXEC="--disable-agent" sh -

To install just the agent without a server we should pass K3S_URL along with K3S_TOKEN or K3S_CLUSTER_SECRET, eg:

curl -sfL https://get.k3s.io | K3S_URL=https://example-url:6443 K3S_TOKEN=XXX sh -

The installer can also be run without performing downloads by setting INSTALL_K3S_SKIP_DOWNLOAD=true, eg:

curl -sfL https://github.com/rancher/k3s/releases/download/vX.Y.Z/k3s -o /usr/local/bin/k3s
chmod 0755 /usr/local/bin/k3s

curl -sfL https://get.k3s.io -o install-k3s.sh
chmod 0755 install-k3s.sh

export INSTALL_K3S_SKIP_DOWNLOAD=true
./install-k3s.sh

The full help text for the install script environment variables are as follows:

• K3S_*

  Environment variables which begin with K3S_ will be preserved for the systemd service to use. Setting K3S_URL without explicitly setting a systemd exec command will default the command to "agent", and we enforce that K3S_TOKEN or K3S_CLUSTER_SECRET is also set.

• INSTALL_K3S_SKIP_DOWNLOAD

  If set to true will not download k3s hash or binary.

• INSTALL_K3S_VERSION

  Version of k3s to download from github. Will attempt to download the latest version if not specified.

• INSTALL_K3S_BIN_DIR

  Directory to install k3s binary, links, and uninstall script to, or use /usr/local/bin as the default

• INSTALL_K3S_SYSTEMD_DIR

  Directory to install systemd service and environment files to, or use /etc/systemd/system as the default

• INSTALL_K3S_EXEC or script arguments

  Command with flags to use for launching k3s in the systemd service, if the command is not specified will default to "agent" if K3S_URL is set or "server" if not. The final systemd command resolves to a combination of EXEC and script args ($@).

  The following commands result in the same behavior:

  curl ... | INSTALL_K3S_EXEC="--disable-agent" sh -s -
  curl ... | INSTALL_K3S_EXEC="server --disable-agent" sh -s -
  curl ... | INSTALL_K3S_EXEC="server" sh -s - --disable-agent
  curl ... | sh -s - server --disable-agent
  curl ... | sh -s - --disable-agent
  

• INSTALL_K3S_NAME

  Name of systemd service to create, will default from the k3s exec command if not specified. If specified the name will be prefixed with 'k3s-'.

• INSTALL_K3S_TYPE

  Type of systemd service to create, will default from the k3s exec command if not specified.

openrc on Alpine Linux

In order to pre-setup Alpine Linux you have to go through the following steps:

echo "cgroup /sys/fs/cgroup cgroup defaults 0 0" >> /etc/fstab

cat >> /etc/cgconfig.conf <<EOF
mount {
cpuacct = /cgroup/cpuacct;
memory = /cgroup/memory;
devices = /cgroup/devices;
freezer = /cgroup/freezer;
net_cls = /cgroup/net_cls;
blkio = /cgroup/blkio;
cpuset = /cgroup/cpuset;
cpu = /cgroup/cpu;
}
EOF

Then update /etc/update-extlinux.conf by adding:

default_kernel_opts="...  cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory"

Than update the config and reboot

update-extlinux
reboot

After rebooting:

• download k3s to /usr/local/bin/k3s
• create an openrc file in /etc/init.d

For the server:

#!/sbin/openrc-run

command=/usr/local/bin/k3s
command_args="server"
pidfile=

name="k3s"
description="Lightweight Kubernetes"

For the agent:

#!/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

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:

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:

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 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

Ports

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 service port below 1024 to the host with an offset of 10000.

That means service port 80 will become 10080 on the host, but 8080 will become 8080 without any offset.

Currently, only LoadBalancer services are automatically bound.

Daemon lifecycle

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.

The issue is tracked in https://github.com/rootless-containers/rootlesskit/issues/65

Cgroups

Cgroups are not supported

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:

curl -sfL https://get.k3s.io | sh -

If you want to upgrade to specific version you can run the following command:

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
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:

sudo systemctl restart k3s

To restart manually for openrc use:

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

Current items to implement before this is to be considered production quality.

1. Multi-Server / High Availability (HA)
2. Documentation moved to Rancher
3. Automated tests for k3s specific features