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K3s Scheduler

New

Introduced in 0.33.0

scheduler-k3s:annotations:set <app|--global> <property> (<value>) [--process-type PROCESS_TYPE] <--resource-type RESOURCE_TYPE>, Set or clear an annotation for a given app/process-type/resource-type combination
scheduler-k3s:cluster-add [ssh://user@host:port]    # Adds a server node to a Dokku-managed cluster
scheduler-k3s:cluster-list                          # Lists all nodes in a Dokku-managed cluster
scheduler-k3s:cluster-remove [node-id]              # Removes client node to a Dokku-managed cluster
scheduler-k3s:initialize                            # Initializes a cluster
scheduler-k3s:report [<app>] [<flag>]               # Displays a scheduler-k3s report for one or more apps
scheduler-k3s:set [<app>|--global] <key> (<value>)  # Set or clear a scheduler-k3s property for an app or the scheduler
scheduler-k3s:show-kubeconfig                       # Displays the kubeconfig for remote usage
scheduler-k3s:uninstall                             # Uninstalls k3s from the Dokku server

Note

The k3s plugin replaces the external scheduler-kubernetes plugin. Users can continue to use the external plugin as necessary, but all future development will occur on the official core k3s plugin.

For multi-server support, Dokku provides the ability for users to setup a K3s cluster. As with all schedulers, it is set on a per-app basis. The scheduler can currently be overridden by running the following command:

dokku scheduler:set node-js-app selected k3s

As it is the default, unsetting the selected scheduler property is also a valid way to reset the scheduler.

dokku scheduler:set node-js-app k3s

Usage

Initializing a cluster

Warning

This command must be run as root

Clusters can be initialized via the scheduler-k3s:initialize command. This will start a k3s cluster on the Dokku node itself.

dokku scheduler-k3s:initialize

By default, the k3s installation can run both app and system workloads. For clusters where app workloads are run on distinct worker nodes, initialize the cluster with the --taint-scheduling flag, which will allow only Critical cluster components on the k3s control-plane nodes.

dokku scheduler-k3s:initialize --taint-scheduling

By default, Dokku will attempt to auto-detect the IP address of the server. In cases where the auto-detected IP address is incorrect, an override may be specified via the --server-ip flag:

dokku scheduler-k3s:initialize --server-ip 192.168.20.15

Dokku's k3s integration natively uses Traefik as it's ingress load balancer via Traefik's CRDs, but a cluster can be set to use nginx via the ingress-nginx project. Switching to nginx will result in any nginx plugin settings being respected, either by turning them into annotations or creating a custom server snippet.

To change the ingress, set the --ingress-class flag:

dokku scheduler-k3s:initialize --ingress-class nginx

Adding nodes to the cluster

Warning

The dokku user must be able to ssh onto the server in order to connect nodes to the cluster. The remote user must be root or have sudo enabled, or the install will fail.

Adding a worker node

Nodes that run app workloads can be added via the scheduler-k3s:cluster-add command. This will ssh onto the specified server, install k3s, and join it to the current Dokku node in worker mode. Workers are typically used to run app workloads.

dokku scheduler-k3s:cluster-add  ssh://root@worker-1.example.com

If the server isn't in the known_hosts file, the connection will fail. This can be bypassed by setting the --insecure-allow-unknown-hosts flag:

dokku scheduler-k3s:cluster-add --insecure-allow-unknown-hosts ssh://root@worker-1.example.com

By default, Dokku will attempt to auto-detect the IP address of the Dokku server for the remote server to connect to. In cases where the auto-detected IP address is incorrect, an override may be specified via the --server-ip flag:

dokku scheduler-k3s:cluster-add --server-ip 192.168.20.15 ssh://root@worker-1.example.com

Adding a server node

Note

Only the initial Dokku server will be properly configured for push deployment, and should be considered your git remote. Additional server nodes are for ensuring high-availability of the K3s etcd state. Ensure this server is properly backed up and restorable or deployments will not work.

Server nodes are typically used to replicate the cluster state, and it is recommended to have an odd number of nodes spread across several availability zones (datacenters in close proximity within a region). This allows for higher availability in the event of a cluster failure. Server nodes run control-plane services such as the traefik load balancer and the etcd backing store.

Server nodes can also be added with the scheduler-k3s:cluster-add command by specifying --role server. This will ssh onto the specified server, install k3s, and join it to the current Dokku node in server mode.

dokku scheduler-k3s:cluster-add  --role server ssh://root@server-1.example.com

Server nodes allow any workloads to be scheduled on them by default, in addition to the control-plane, etcd, and the scheduler itself. To avoid app workloads being scheduled on your control-plane, use the --taint-scheduling flag:

dokku scheduler-k3s:cluster-add --role server --taint-scheduling ssh://root@server-1.example.com

If the server isn't in the known_hosts file, the connection will fail. This can be bypassed by setting the --insecure-allow-unknown-hosts flag:

dokku scheduler-k3s:cluster-add --role server --insecure-allow-unknown-hosts ssh://root@server-1.example.com

By default, Dokku will attempt to auto-detect the IP address of the Dokku server for the remote server to connect to. In cases where the auto-detected IP address is incorrect, an override may be specified via the --server-ip flag:

dokku scheduler-k3s:cluster-add --role server --server-ip 192.168.20.15 ssh://root@server-1.example.com

Changing the network interface

When attaching an worker or server node, the K3s plugin will look at the IP associated with the eth0 interface and use that to connect the new node to the cluster. To change this, set the network-interface property to the appropriate value.

dokku scheduler-k3s:set --global network-interface eth1

Changing deploy timeouts

By default, app deploys will timeout after 300s. To customize this value, set the deploy-timeout property via scheduler-k3s:set:

dokku scheduler-k3s:set node-js-app deploy-timeout 60s

The default value may be set by passing an empty value for the option:

dokku scheduler-k3s:set node-js-app deploy-timeout

The deploy-timeout property can also be set globally. The global default is 300s.

dokku scheduler-k3s:set --global deploy-timeout 60s

The default value may be set by passing an empty value for the option.

dokku scheduler-k3s:set --global deploy-timeout

Customizing the namespace

By default, app deploys will run against the default Kubernetes namespace. To customize this value, set the namespace property via scheduler-k3s:set:

dokku scheduler-k3s:set node-js-app namespace lollipop

The default value may be set by passing an empty value for the option:

dokku scheduler-k3s:set node-js-app namespace

The namespace property can also be set globally. The global default is default.

dokku scheduler-k3s:set --global namespace 60s

The default value may be set by passing an empty value for the option.

dokku scheduler-k3s:set --global namespace

Enabling rollback on failure

By default, app deploys do not rollback on failure. To enable this functionality, set the rollback-on-failure property via scheduler-k3s:set:

dokku scheduler-k3s:set node-js-app rollback-on-failure true

The default value may be set by passing an empty value for the option:

dokku scheduler-k3s:set node-js-app rollback-on-failure

The rollback-on-failure property can also be set globally. The global default is false.

dokku scheduler-k3s:set --global rollback-on-failure false

The default value may be set by passing an empty value for the option.

dokku scheduler-k3s:set --global rollback-on-failure

Using image pull secrets

When authenticating against a registry via registry:login, the scheduler-k3s plugin will authenticate all servers in the cluster against the registry specified. If desired, an image pull secret can be used instead. To customize this value, set the image-pull-secrets property via scheduler-k3s:set:

dokku scheduler-k3s:set node-js-app image-pull-secrets lollipop

The default value may be set by passing an empty value for the option:

dokku scheduler-k3s:set node-js-app image-pull-secrets

The image-pull-secrets property can also be set globally. The global default is empty string, and k3s will use Dokku's locally configured ~/.docker/config.json for any private registry pulls.

dokku scheduler-k3s:set --global image-pull-secrets 60s

The default value may be set by passing an empty value for the option.

dokku scheduler-k3s:set --global image-pull-secrets

Enabling letsencrypt integration

By default, letsencrypt is disabled and https port mappings are ignored. To enable, set the letsencrypt-email-prod or letsencrypt-email-stag property with the --global flag:

# set the value for prod
dokku scheduler-k3s:set --global letsencrypt-email-prod automated@dokku.sh

# set the value for stag
dokku scheduler-k3s:set --global letsencrypt-email-stag automated@dokku.sh

After enabling and rebuilding, all apps with an http:80 port mapping will have a corresponding https:443 added and ssl will be automatically enabled. All http requests will then be redirected to https.

Customizing the letsencrypt server

The letsencrypt integration is set to the production letsencrypt server by default. This can be changed on an app-level by setting the letsencrypt-server property with the scheduler-k3s:set command

dokku scheduler-k3s:set node-js-app letsencrypt-server staging

The default value may be set by passing an empty value for the option:

dokku scheduler-k3s:set node-js-app letsencrypt-server

The image-pull-secrets property can also be set globally. The global default is production.

dokku scheduler-k3s:set --global letsencrypt-server staging

The default value may be set by passing an empty value for the option.

dokku scheduler-k3s:set --global letsencrypt-server staging

Customizing Annotations and Labels

Note

The cron ID is used as the process type if your app deploys any cron tasks

Setting Annotations

Dokku injects certain annotations into each created resource by default, but it may be necessary to inject others for tighter integration with third-party tools. The scheduler-k3s:annotations:set command can be used to perform this task. The command takes an app name and a required --resource-type flag.

dokku scheduler-k3s:annotations:set node-js-app annotation.key annotation.value --resource-type deployment

If not specified, the annotation will be applied to all processes within an app, though it may be further scoped to a specific process type via the --process-type flag.

dokku scheduler-k3s:annotations:set node-js-app annotation.key annotation.value --resource-type deployment --process-type web

The following resource types are supported:

  • certificate
  • cronjob
  • deployment
  • ingress
  • job
  • pod
  • secret
  • service
  • serviceaccount
  • traefik_ingressroute
  • traefik_middleware

Removing an annotation

To unset an annotation, pass an empty value:

dokku scheduler-k3s:annotations:set node-js-app annotation.key --resource-type deployment
dokku scheduler-k3s:annotations:set node-js-app annotation.key --resource-type deployment --process-type web

Setting Labels

Dokku injects certain labels into each created resource by default, but it may be necessary to inject others for tighter integration with third-party tools. The scheduler-k3s:labels:set command can be used to perform this task. The command takes an app name and a required --resource-type flag.

dokku scheduler-k3s:labels:set node-js-app label.key label.value --resource-type deployment

If not specified, the label will be applied to all processes within an app, though it may be further scoped to a specific process type via the --process-type flag.

dokku scheduler-k3s:labels:set node-js-app label.key label.value --resource-type deployment --process-type web

The following resource types are supported:

  • certificate
  • cronjob
  • deployment
  • ingress
  • job
  • pod
  • secret
  • service
  • serviceaccount
  • traefik_ingressroute
  • traefik_middleware

Removing a label

To unset an label, pass an empty value:

dokku scheduler-k3s:annotations:set node-js-app label.key --resource-type deployment
dokku scheduler-k3s:labels:set node-js-app label.key --resource-type deployment --process-type web

Using kubectl remotely

Warning

Certain ports must be open for interacting with the remote kubernets api. Refer to the K3s networking documentation for the required open ports between servers prior to running the command.

By default, Dokku assumes that all it controls all actions on the cluster, and thus does not expose the kubectl binary for administrators. To interact with kubectl, you will need to retrieve the kubeconfig for the cluster and configure your client to use that configuration.

dokku scheduler-k3s:show-kubeconfig

Interacting with an external Kubernetes cluster

While the k3s scheduler plugin is designed to work with a Dokku-managed k3s cluster, Dokku can be configured to interact with any Kubernetes cluster by setting the global kubeconfig-path to a path to a custom kubeconfig on the Dokku server. This property is only available at a global level.

dokku scheduler-k3s:set --global kubeconfig-path /path/to/custom/kubeconfig

To set the default value, omit the value from the scheduler-k3s:set call:

dokku scheduler-k3s:set --global kubeconfig-path

The default value for the kubeconfig-path is the k3s kubeconfig located at /etc/rancher/k3s/k3s.yaml.

Customizing the Kubernetes context

When interacting with a custom Kubeconfig, the kube-context property can be set to specify a specific context within the kubeconfig to use. This property is available only at the global leve.

dokku scheduler-k3s:set --global kube-context lollipop

To set the default value, omit the value from the scheduler-k3s:set call:

dokku scheduler-k3s:set --global kube-context

The default value for the kube-context is an empty string, and will result in Dokku using the current context within the kubeconfig.

Scheduler Interface

The following sections describe implemented and unimplemented scheduler functionality for the k3s scheduler.

Implemented Commands and Triggers

This plugin implements various functionality through plugn triggers to integrate with Docker for running apps on a single server. The following functionality is supported by the scheduler-k3s plugin.

  • apps:clone
  • apps:destroy
  • apps:rename
  • cron
  • enter
  • deploy
  • healthchecks
    • Due to Kubernetes limitations, only a single healthcheck is supported for each of the liveness, readiness, and startup healthchecks
    • Due to Kubernetes limitations, content checks are not supported
    • Ports specified in the app.json are ignored in favor of the container port on the port mapping detected
  • logs
  • ps:stop
  • run
    • The scheduler-post-run trigger is not always triggered
  • run:detached
  • run:list

Unimplemented command functionality

  • run:logs
  • ps:inspect

The following Dokku functionality is not implemented at this time.

  • vector log integration
  • persistent storage

Logging support

App logs for the logs command are fetched by Dokku from running containers via the kubectl cli. Persisting logs via Vector is not implemented at this time. Users may choose to configure the Vector Kubernetes integration directly by following this guide.

Supported Resource Management Properties

The k3s scheduler supports a minimal list of resource limits and reservations:

  • cpu: is specified in number of CPUs a process can access.
  • memory: should be specified with a suffix of b (bytes), Ki (kilobytes), Mi (megabytes), Gi (gigabytes). Default unit is Mi (megabytes).

If unspecified for any task, the default reservation will be .1 CPU and 128Mi RAM, with no limit set for either CPU or RAM. This is to avoid issues with overscheduling pods on a cluster. To avoid issues, set more specific values for at least resource reservations. If unbounded utilization is desired, set CPU and Memory to 0m and 0Mi, respectively.

Note

Cron tasks retrieve resource limits based on the computed cron task ID.