Draino automatically drains Kubernetes nodes based on labels and node
conditions. Nodes that match all of the supplied labels and any of the
supplied node conditions will be cordoned immediately and drained after a
configurable drain-buffer time.
Draino is intended for use alongside the Kubernetes Node Problem Detector and Cluster Autoscaler. The Node Problem Detector can set a node condition when it detects something wrong with a node - for instance by watching node logs or running a script. The Cluster Autoscaler can be configured to delete nodes that are underutilised. Adding Draino to the mix enables autoremediation:
- The Node Problem Detector detects a permanent node problem and sets the corresponding node condition.
- Draino notices the node condition. It immediately cordons the node to prevent new pods being scheduled there, and schedules a drain of the node.
- Once the node has been drained the Cluster Autoscaler will consider it underutilised. It will be eligible for scale down (i.e. termination) by the Autoscaler after a configurable period of time.
$ docker run planetlabs/draino /draino --help
usage: draino [<flags>] <node-conditions>...
Automatically cordons and drains nodes that match the supplied conditions.
Flags:
--help Show context-sensitive help (also try --help-long and --help-man).
-d, --debug Run with debug logging.
--listen=":10002" Address at which to expose /metrics and /healthz.
--kubeconfig=KUBECONFIG Path to kubeconfig file. Leave unset to use in-cluster config.
--master=MASTER Address of Kubernetes API server. Leave unset to use in-cluster config.
--dry-run Emit an event without cordoning or draining matching nodes.
--max-grace-period=8m0s Maximum time evicted pods will be given to terminate gracefully.
--eviction-headroom=30s Additional time to wait after a pod's termination grace period for it to have been deleted.
--drain-buffer=10m0s Minimum time between starting each drain. Nodes are always cordoned immediately.
--node-label="foo=bar" (DEPRECATED) Only nodes with this label will be eligible for cordoning and draining. May be specified multiple times.
--node-label-expr="metadata.labels.foo == 'bar'"
This is an expr string https://github.com/antonmedv/expr that must return true or false. See `nodefilters_test.go` for examples
--namespace="kube-system" Namespace used to create leader election lock object.
--leader-election-lease-duration=15s
Lease duration for leader election.
--leader-election-renew-deadline=10s
Leader election renew deadline.
--leader-election-retry-period=2s
Leader election retry period.
--skip-drain Whether to skip draining nodes after cordoning.
--evict-daemonset-pods Evict pods that were created by an extant DaemonSet.
--evict-emptydir-pods Evict pods with local storage, i.e. with emptyDir volumes.
--evict-unreplicated-pods Evict pods that were not created by a replication controller.
--disable-eviction Force drain to use delete, even if eviction is supported. This will bypass checking PodDisruptionBudget.
--keep-retry-drain Keep retry draining after failed drain.
--protected-pod-annotation=KEY[=VALUE] ...
Protect pods with this annotation from eviction. May be specified multiple times.
Args:
<node-conditions> Nodes for which any of these conditions are true will be cordoned and drained.
Draino allows filtering the elligible set of nodes using --node-label and --node-label-expr.
The original flag --node-label is limited to the boolean AND of the specified labels. To express more complex predicates, the new --node-label-expr
flag allows for mixed OR/AND/NOT logic via https://github.com/antonmedv/expr.
An example of --node-label-expr:
(metadata.labels.region == 'us-west-1' && metadata.labels.app == 'nginx') || (metadata.labels.region == 'us-west-2' && metadata.labels.app == 'nginx')
Keep the following in mind before deploying Draino:
- Always run Draino in
--dry-runmode first to ensure it would drain the nodes you expect it to. In dry run mode Draino will emit logs, metrics, and events but will not actually cordon or drain nodes. - Draino immediately cordons nodes that match its configured labels and node conditions, but will wait a configurable amount of time (10 minutes by default) between draining nodes. i.e. If two nodes begin exhibiting a node condition simultaneously one node will be drained immediately and the other in 10 minutes.
- Draino considers a drain to have failed if at least one pod eviction triggered by that drain fails. If Draino fails to evict two of five pods it will consider the Drain to have failed, but the remaining three pods will always be evicted.
- Pods that can't be evicted by the cluster-autoscaler won't be evicted by draino.
See annotation
"cluster-autoscaler.kubernetes.io/safe-to-evict": "false"in cluster-autoscaler documentation
Draino is automatically built from master and pushed to the Docker Hub.
Builds are tagged planetlabs/draino:$(git rev-parse --short HEAD).
Note: As of September, 2020 we no longer publish planetlabs/draino:latest
in order to encourage explicit and pinned releases.
An example Kubernetes deployment manifest is provided.
Draino provides a simple healthcheck endpoint at /healthz and Prometheus
metrics at /metrics. The following metrics exist:
$ kubectl -n kube-system exec -it ${DRAINO_POD} -- apk add curl
$ kubectl -n kube-system exec -it ${DRAINO_POD} -- curl http://localhost:10002/metrics
# HELP draino_cordoned_nodes_total Number of nodes cordoned.
# TYPE draino_cordoned_nodes_total counter
draino_cordoned_nodes_total{result="succeeded"} 2
draino_cordoned_nodes_total{result="failed"} 1
# HELP draino_drained_nodes_total Number of nodes drained.
# TYPE draino_drained_nodes_total counter
draino_drained_nodes_total{result="succeeded"} 1
draino_drained_nodes_total{result="failed"} 1Draino is generating event for every relevant step of the eviction process. Here is an example that ends with a reason DrainFailed. When everything is fine the last event for a given node will have a reason DrainSucceeded.
> kubectl get events -n default | grep -E '(^LAST|draino)'
LAST SEEN FIRST SEEN COUNT NAME KIND TYPE REASON SOURCE MESSAGE
5m 5m 1 node-demo.15fe0c35f0b4bd10 Node Warning CordonStarting draino Cordoning node
5m 5m 1 node-demo.15fe0c35fe3386d8 Node Warning CordonSucceeded draino Cordoned node
5m 5m 1 node-demo.15fe0c360bd516f8 Node Warning DrainScheduled draino Will drain node after 2020-03-20T16:19:14.91905+01:00
5m 5m 1 node-demo.15fe0c3852986fe8 Node Warning DrainStarting draino Draining node
4m 4m 1 node-demo.15fe0c48d010ecb0 Node Warning DrainFailed draino Draining failed: timed out waiting for evictions to complete: timed out
When a drain is scheduled, on top of the event, a condition is added to the status of the node. This condition will hold information about the beginning and the end of the drain procedure. This is something that you can see by describing the node resource:
> kubectl describe node {node-name}
......
Unschedulable: true
Conditions:
Type Status LastHeartbeatTime LastTransitionTime Reason Message
---- ------ ----------------- ------------------ ------ -------
OutOfDisk False Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:01:59 +0100 KubeletHasSufficientDisk kubelet has sufficient disk space available
MemoryPressure False Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:01:59 +0100 KubeletHasSufficientMemory kubelet has sufficient memory available
DiskPressure False Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:01:59 +0100 KubeletHasNoDiskPressure kubelet has no disk pressure
PIDPressure False Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:01:59 +0100 KubeletHasSufficientPID kubelet has sufficient PID available
Ready True Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:02:09 +0100 KubeletReady kubelet is posting ready status. AppArmor enabled
ec2-host-retirement True Fri, 20 Mar 2020 15:23:26 +0100 Fri, 20 Mar 2020 15:23:26 +0100 NodeProblemDetector Condition added with tooling
DrainScheduled True Fri, 20 Mar 2020 15:50:50 +0100 Fri, 20 Mar 2020 15:23:26 +0100 Draino Drain activity scheduled 2020-03-20T15:50:34+01:00
Later when the drain activity will be completed the condition will be amended letting you know if it succeeded of failed:
> kubectl describe node {node-name}
......
Unschedulable: true
Conditions:
Type Status LastHeartbeatTime LastTransitionTime Reason Message
---- ------ ----------------- ------------------ ------ -------
OutOfDisk False Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:01:59 +0100 KubeletHasSufficientDisk kubelet has sufficient disk space available
MemoryPressure False Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:01:59 +0100 KubeletHasSufficientMemory kubelet has sufficient memory available
DiskPressure False Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:01:59 +0100 KubeletHasNoDiskPressure kubelet has no disk pressure
PIDPressure False Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:01:59 +0100 KubeletHasSufficientPID kubelet has sufficient PID available
Ready True Fri, 20 Mar 2020 15:52:41 +0100 Fri, 20 Mar 2020 14:02:09 +0100 KubeletReady kubelet is posting ready status. AppArmor enabled
ec2-host-retirement True Fri, 20 Mar 2020 15:23:26 +0100 Fri, 20 Mar 2020 15:23:26 +0100 NodeProblemDetector Condition added with tooling
DrainScheduled True Fri, 20 Mar 2020 15:50:50 +0100 Fri, 20 Mar 2020 15:23:26 +0100 Draino Drain activity scheduled 2020-03-20T15:50:34+01:00 | Completed: 2020-03-20T15:50:50+01:00
If the drain had failed the condition line would look like:
DrainScheduled True Fri, 20 Mar 2020 15:50:50 +0100 Fri, 20 Mar 2020 15:23:26 +0100 Draino Drain activity scheduled 2020-03-20T15:50:34+01:00| Failed:2020-03-20T15:55:50+01:00
In some cases the drain activity may failed because of restrictive Pod Disruption Budget or any other reason external to Draino. The node remains cordon and the drain condition
is marked as Failed. If you want to reschedule a drain tentative on that node, add the annotation: draino/drain-retry: true. A new drain schedule will be created. Note that the annotation is not modified and will trigger retries in loop in case the drain fails again.
kubectl annotate node {node-name} draino/drain-retry=true
Draino can be run in dry run mode using the --dry-run flag.
Draino can also optionally be run in a mode where the nodes are only cordoned, and not drained. This can be achieved by using the --skip-drain flag.