CSI provisioner
The external-provisioner is a sidecar container that dynamically provisions volumes by calling CreateVolume and DeleteVolume functions of CSI drivers. It is necessary because internal persistent volume controller running in Kubernetes controller-manager does not have any direct interfaces to CSI drivers.
Overview
The external-provisioner is an external controller that monitors PersistentVolumeClaim objects created by user and creates/deletes volumes for them.
The Kubernetes Container Storage Interface (CSI) Documentation explains how to develop, deploy, and test a Container Storage Interface (CSI) driver on Kubernetes.
Compatibility
This information reflects the head of this branch.
Feature status
Various external-provisioner releases come with different alpha / beta features. Check --help output for alpha/beta features in each release.
Following table reflects the head of this branch.
All other external-provisioner features and the external-provisioner itself is considered GA and fully supported.
Usage
It is necessary to create a new service account and give it enough privileges to run the external-provisioner, see deploy/kubernetes/rbac.yaml. The provisioner is then deployed as single Deployment as illustrated below:
kubectl create deploy/kubernetes/deployment.yaml
The external-provisioner may run in the same pod with other external CSI controllers such as the external-attacher, external-snapshotter and/or external-resizer.
Note that the external-provisioner does not scale with more replicas. Only one external-provisioner is elected as leader and running. The others are waiting for the leader to die. They re-elect a new active leader in ~15 seconds after death of the old leader.
Command line options
Recommended optional arguments
-
--csi-address <path to CSI socket>: This is the path to the CSI driver socket inside the pod that the external-provisioner container will use to issue CSI operations (/run/csi/socket is used by default).
-
--leader-election: Enables leader election. This is mandatory when there are multiple replicas of the same external-provisioner running for one CSI driver. Only one of them may be active (=leader). A new leader will be re-elected when current leader dies or becomes unresponsive for ~15 seconds.
-
--leader-election-namespace: Namespace where leader election object will be created. It is recommended that this parameter is populated from Kubernetes DownwardAPI with the namespace where the external-provisioner runs in.
-
--leader-election-lease-duration <duration>: Duration, in seconds, that non-leader candidates will wait to force acquire leadership. Defaults to 15 seconds.
-
--leader-election-renew-deadline <duration>: Duration, in seconds, that the acting leader will retry refreshing leadership before giving up. Defaults to 10 seconds.
-
--leader-election-retry-period <duration>: Duration, in seconds, the LeaderElector clients should wait between tries of actions. Defaults to 5 seconds.
-
--timeout <duration>: Timeout of all calls to CSI driver. It should be set to value that accommodates majority of ControllerCreateVolume and ControllerDeleteVolume calls. See CSI error and timeout handling for details. 15 seconds is used by default.
-
--retry-interval-start <duration>: Initial retry interval of failed provisioning or deletion. It doubles with each failure, up to --retry-interval-max and then it stops increasing. Default value is 1 second. See CSI error and timeout handling for details.
-
--retry-interval-max <duration>: Maximum retry interval of failed provisioning or deletion. Default value is 5 minutes. See CSI error and timeout handling for details.
-
--worker-threads <num>: Number of simultaneously running ControllerCreateVolume and ControllerDeleteVolume operations. Default value is 100.
-
--kube-api-qps <num>: The number of requests per second sent by a Kubernetes client to the Kubernetes API server. Defaults to 5.0.
-
--kube-api-burst <num>: The number of requests to the Kubernetes API server, exceeding the QPS, that can be sent at any given time. Defaults to 10.
-
--cloning-protection-threads <num>: Number of simultaneously running threads, handling cloning finalizer removal. Defaults to 1.
-
--snapshot-orphan-sweep-interval <duration>: How often to check for orphaned snapshot source-protection finalizers. These finalizers can become stuck if the provisioner crashes during snapshot-based provisioning. Set to 0 to disable. Defaults to 5m.
-
--http-endpoint: The TCP network address where the HTTP server for diagnostics, including metrics and leader election health check, will listen (example: :8080 which corresponds to port 8080 on local host). The default is empty string, which means the server is disabled.
-
--metrics-path: The HTTP path where prometheus metrics will be exposed. Default is /metrics.
-
--extra-create-metadata: Enables the injection of extra PVC and PV metadata as parameters when calling CreateVolume on the driver (keys: “csi.storage.k8s.io/pvc/name”, “csi.storage.k8s.io/pvc/namespace”, “csi.storage.k8s.io/pv/name”)
-
controller-publish-readonly: This option enables PV to be marked as readonly at controller publish volume call if PVC accessmode has been set to ROX. Defaults to false.
-
--enable-pprof: Enable pprof profiling on the TCP network address specified by --http-endpoint. The HTTP path is /debug/pprof/.
Storage capacity arguments
See the storage capacity section below for details.
-
--enable-capacity: This enables producing CSIStorageCapacity objects with capacity information from the driver’s GetCapacity call. The default is to not produce CSIStorageCapacity objects.
-
--capacity-ownerref-level <levels>: The level indicates the number of objects that need to be traversed starting from the pod identified by the POD_NAME and NAMESPACE environment variables to reach the owning object for CSIStorageCapacity objects: 0 for the pod itself, 1 for a StatefulSet and DaemonSet, 2 for a Deployment, etc. Defaults to 1 (= StatefulSet). Ownership is optional and can be disabled with -1.
-
--capacity-threads <num>: Number of simultaneously running threads, handling CSIStorageCapacity objects. Defaults to 1.
-
--capacity-poll-interval <interval>: How long the external-provisioner waits before checking for storage capacity changes. Defaults to 1m.
-
--capacity-for-immediate-binding <bool>: Enables producing capacity information for storage classes with immediate binding. Not needed for the Kubernetes scheduler, maybe useful for other consumers or for debugging. Defaults to false.
Distributed provisioning
-
--node-deployment: Enables deploying the external-provisioner together with a CSI driver on nodes to manage node-local volumes. Off by default.
-
--node-deployment-immediate-binding: Determines whether immediate binding is supported when deployed on each node. Enabled by default, use --node-deployment-immediate-binding=false if not desired. Disabling it may be useful for example when a custom controller will select nodes for PVCs.
-
--node-deployment-base-delay: Determines how long the external-provisioner sleeps initially before trying to own a PVC with immediate binding. Defaults to 20 seconds.
-
--node-deployment-max-delay: Determines how long the external-provisioner sleeps at most before trying to own a PVC with immediate binding. Defaults to 60 seconds.
Other recognized arguments
-
--feature-gates <gates>: A set of comma separated <feature-name>=<true|false> pairs that describe feature gates for alpha/experimental features. See list of features or --help output for list of recognized features. Example: --feature-gates Topology=true to enable Topology feature that’s disabled by default.
-
--strict-topology: This controls what topology information is passed to CreateVolumeRequest.AccessibilityRequirements in case of delayed binding. See the table below for an explanation how this option changes the result. This option has no effect if either Topology feature is disabled or Immediate volume binding mode is used.
-
--immediate-topology: This controls what topology information is passed to CreateVolumeRequest.AccessibilityRequirements in case of immediate binding. See the table below for an explanation how this option changes the result. This option has no effect if either Topology feature is disabled or WaitForFirstConsumer (= delayed) volume binding mode is used. The default is true, so use --immediate-topology=false to disable it. It should not be disabled if the CSI driver might create volumes in a topology segment that is not accessible in the cluster. Such a driver should use the topology information to create new volumes where they can be accessed.
-
--kubeconfig <path>: Path to Kubernetes client configuration that the external-provisioner uses to connect to Kubernetes API server. When omitted, default token provided by Kubernetes will be used. This option is useful only when the external-provisioner does not run as a Kubernetes pod, e.g. for debugging. Either this or --master needs to be set if the external-provisioner is being run out of cluster.
-
--master <url>: Master URL to build a client config from. When omitted, default token provided by Kubernetes will be used. This option is useful only when the external-provisioner does not run as a Kubernetes pod, e.g. for debugging. Either this or --kubeconfig needs to be set if the external-provisioner is being run out of cluster.
-
--metrics-address: (deprecated) The TCP network address where the prometheus metrics endpoint will run (example: :8080 which corresponds to port 8080 on local host). The default is empty string, which means metrics endpoint is disabled.
-
--volume-name-prefix <prefix>: Prefix of PersistentVolume names created by the external-provisioner. Default value is “pvc”, i.e. created PersistentVolume objects will have name pvc-<uuid>.
-
--volume-name-uuid-length: Length of UUID to be added to --volume-name-prefix. Default behavior is to NOT truncate the UUID.
-
--version: Prints current external-provisioner version and quits.
-
--prevent-volume-mode-conversion: Prevents an unauthorized user from modifying the volume mode when creating a PVC from an existing VolumeSnapshot. Defaults to true.
-
--automaxprocs: Automatically set the GOMAXPROCS environment variable to match the configured Linux container CPU quota. Defaults to false.
-
All glog / klog arguments are supported, such as -v <log level> or -alsologtostderr.
Design
External-provisioner interacts with Kubernetes by watching PVCs and
PVs and implementing the external provisioner
protocol.
The design document explains this in more detail.
Topology support
When Topology feature is enabled* and the driver specifies VOLUME_ACCESSIBILITY_CONSTRAINTS in its plugin capabilities, external-provisioner prepares CreateVolumeRequest.AccessibilityRequirements while calling Controller.CreateVolume. The driver has to consider these topology constraints while creating the volume. Below table shows how these AccessibilityRequirements are prepared:
| Delayed binding |
Strict topology |
Allowed topologies |
Immediate Topology |
Resulting accessibility requirements |
| Yes |
Yes |
Irrelevant |
Irrelevant |
Requisite = Preferred = Selected node topology |
| Yes |
No |
No |
Irrelevant |
Requisite = Aggregated cluster topology
Preferred = Requisite with selected node topology as first element |
| Yes |
No |
Yes |
Irrelevant |
Requisite = Allowed topologies
Preferred = Requisite with selected node topology as first element |
| No |
Irrelevant |
Yes |
Irrelevant |
Requisite = Allowed topologies
Preferred = Requisite rotated so that the entry selected by a hash of the PVC name comes first |
| No |
Irrelevant |
No |
Yes |
Requisite = Aggregated cluster topology
Preferred = Requisite rotated so that the entry selected by a hash of the PVC name comes first |
| No |
Irrelevant |
No |
No |
Requisite and Preferred both nil |
*) Topology feature gate is enabled by default since v5.0.
Aggregated cluster topology is computed from the topology keys that the driver has registered in the CSINode objects. Nodes are not required to register the same topology keys: a driver may report a finer granularity on part of the cluster than on the rest, for example region on some nodes and region plus zone on others. Every distinct registered key set is aggregated separately and the results are combined, so Requisite describes each granularity the cluster offers and no node is excluded because it reports fewer keys than another. A node is only aggregated under the keys that its CSINode registered for the driver: a node that carries topology labels but whose driver reported no topology keys, or is not registered at all, is not included. As a result, the entries in Requisite are not guaranteed to all use the same topology keys. Requisite is a list the driver selects from, so a driver that registers several granularities should pick the entry that suits the volume it is creating, and report the topology the volume was actually created in through CreateVolumeResponse.accessible_topology. Preferred for immediate binding is a rotation of Requisite used to spread StatefulSet volumes, so it contains the same mix of key sets in rotated order: its first entry is not guaranteed to use any particular key set, and a driver should scan it for an entry it can satisfy rather than assuming the first one fits. With delayed binding, only the selected node’s key set is used, and it is aggregated across the nodes that registered it. Clusters where every node that carries topology labels has registered the same topology keys get a single key set, as before.
When enabling topology support in a CSI driver that had it disabled, please make sure the topology is first enabled in the driver’s node DaemonSet and topology labels are populated on all nodes. The topology can be then updated in the driver’s Deployment and its external-provisioner sidecar.
Capacity support
The external-provisioner can be used to create CSIStorageCapacity
objects that hold information about the storage capacity available
through the driver. The Kubernetes scheduler then uses that
information
when selecting nodes for pods with unbound volumes that wait for the
first consumer.
All CSIStorageCapacity objects created by an instance of
the external-provisioner have certain labels:
csi.storage.k8s.io/drivername: the CSI driver namecsi.storage.k8s.io/managed-by: external-provisioner for central
provisioning, external-provisioner- for distributed
provisioning
They get created in the namespace identified with the NAMESPACE
environment variable.
Each external-provisioner instance manages exactly those objects with
the labels that correspond to the instance.
Optionally, all CSIStorageCapacity objects created by an instance of
the external-provisioner can have an
owner.
This ensures that the objects get removed automatically when uninstalling
the CSI driver. The owner is
determined with the POD_NAME/NAMESPACE environment variables and
the --capacity-ownerref-level parameter. Setting an owner reference is highly
recommended whenever possible (i.e. in the most common case that drivers are
run inside containers).
If ownership is disabled the storage admin is responsible for removing
orphaned CSIStorageCapacity objects, and the following command can be
used to clean up orphaned objects of a driver:
kubectl delete csistoragecapacities -l csi.storage.k8s.io/drivername=my-csi.example.com
When switching from a deployment without ownership to one with
ownership, managed objects get updated such that they have the
configured owner. When switching in the other direction, the owner
reference is not removed because the new deployment doesn’t know
what the old owner was.
To enable this feature in a driver deployment with a central controller (see also the
deploy/kubernetes/storage-capacity.yaml
example):
- Set the
POD_NAME and NAMESPACE environment variables like this:
env:
- name: NAMESPACE
valueFrom:
fieldRef:
fieldPath: metadata.namespace
- name: POD_NAME
valueFrom:
fieldRef:
fieldPath: metadata.name
- Add
--enable-capacity to the command line flags.
- Add
StorageCapacity: true to the CSIDriver information object.
Without it, external-provisioner will publish information, but the
Kubernetes scheduler will ignore it. This can be used to first
deploy the driver without that flag, then when sufficient
information has been published, enabled the scheduler usage of it.
- If external-provisioner is not deployed with a StatefulSet, then
configure with
--capacity-ownerref-level which object is meant to own
CSIStorageCapacity objects.
- Optional: configure how often external-provisioner polls the driver
to detect changed capacity with
--capacity-poll-interval.
- Optional: configure how many worker threads are used in parallel
with
--capacity-threads.
- Optional: enable producing information also for storage classes that
use immediate volume binding with
--capacity-for-immediate-binding. This is usually not needed
because such volumes are created by the driver without involving the
Kubernetes scheduler and thus the published information would just
be ignored.
To determine how many different topology segments exist,
external-provisioner uses the topology keys and labels that the CSI
driver instance on each node reports to kubelet in the
NodeGetInfoResponse.accessible_topology field. The keys are stored
by kubelet in the CSINode objects and the actual values in Node
annotations.
CSI drivers must report topology information that matches the storage
pool(s) that it has access to, with granularity that matches the most
restrictive pool.
For example, if the driver runs in a node with region/rack topology
and has access to per-region storage as well as per-rack storage, then
the driver should report topology with region/rack as its keys. If it
only has access to per-region storage, then it should just use region
as key. If it uses region/rack, then redundant CSIStorageCapacity
objects will be published, but the information is still correct. See
the
KEP
for details.
For each segment and each storage class, CSI GetCapacity is called
once with the topology of the segment and the parameters of the
class. If there is no error and the capacity is non-zero, a
CSIStorageCapacity object is created or updated (if it
already exists from a prior call) with that information. Obsolete
objects are removed.
To ensure that CSIStorageCapacity objects get removed when the
external-provisioner gets removed from the cluster, they all have an
owner and therefore get garbage-collected when that owner
disappears. The owner is not the external-provisioner pod itself but
rather one of its parents as specified by --capacity-ownerref-level.
This way, it is possible to switch between external-provisioner
instances without losing the already gathered information.
CSIStorageCapacity objects are namespaced and get created in the
namespace of the external-provisioner. Only CSIStorageCapacity objects
with the right owner are modified by external-provisioner and their
name is generated, so it is possible to deploy different drivers in
the same namespace. However, Kubernetes does not check who is creating
CSIStorageCapacity objects, so in theory a malfunctioning or malicious
driver deployment could also publish incorrect information about some
other driver.
The deployment with distributed
provisioning is almost the same as above,
with some minor change:
- Use
--capacity-ownerref-level=1 and the NAMESPACE/POD_NAME
variables to make the DaemonSet that contains the external-provisioner
the owner of CSIStorageCapacity objects for the node.
Deployments of external-provisioner outside the Kubernetes cluster
are also possible, albeit only without an owner for the objects.
NAMESPACE still needs to be set to some existing namespace also
in this case.
CSI error and timeout handling
The external-provisioner invokes all gRPC calls to CSI driver with timeout provided by --timeout command line argument (15 seconds by default).
Correct timeout value and number of worker threads depends on the storage backend and how quickly it is able to process ControllerCreateVolume and ControllerDeleteVolume calls. The value should be set to accommodate majority of them. It is fine if some calls time out - such calls will be retried after exponential backoff (starting with 1s by default), however, this backoff will introduce delay when the call times out several times for a single volume.
Frequency of ControllerCreateVolume and ControllerDeleteVolume retries can be configured by --retry-interval-start and --retry-interval-max parameters. The external-provisioner starts retries with retry-interval-start interval (1s by default) and doubles it with each failure until it reaches retry-interval-max (5 minutes by default). The external provisioner stops increasing the retry interval when it reaches retry-interval-max, however, it still retries provisioning/deletion of a volume until it’s provisioned. The external-provisioner keeps its own number of provisioning/deletion failures for each volume.
The external-provisioner can invoke up to --worker-threads (100 by default) ControllerCreateVolume and up to --worker-threads (100 by default) ControllerDeleteVolume calls in parallel, i.e. these two calls are counted separately. The external-provisioner assumes that the storage backend can cope with such high number of parallel requests and that the requests are handled in relatively short time (ideally sub-second). Lower value should be used for storage backends that expect slower processing related to newly created / deleted volumes or can handle lower amount of parallel calls.
Details of error handling of individual CSI calls:
ControllerCreateVolume: The call might have timed out just before the driver provisioned a volume and was sending a response. From that reason, timeouts from ControllerCreateVolume is considered as “volume may be provisioned” or “volume is being provisioned in the background.” The external-provisioner will retry calling ControllerCreateVolume after exponential backoff until it gets either successful response or final (non-timeout) error that the volume cannot be created.ControllerDeleteVolume: This is similar to ControllerCreateVolume, The external-provisioner will retry calling ControllerDeleteVolume with exponential backoff after timeout until it gets either successful response or a final error that the volume cannot be deleted.Probe: The external-provisioner retries calling Probe until the driver reports it’s ready. It retries also when it receives timeout from Probe call. The external-provisioner has no limit of retries. It is expected that ReadinessProbe on the driver container will catch case when the driver takes too long time to get ready.GetPluginInfo, GetPluginCapabilitiesRequest, ControllerGetCapabilities: The external-provisioner expects that these calls are quick and does not retry them on any error, including timeout. Instead, it assumes that the driver is faulty and exits. Note that Kubernetes will likely start a new provisioner container and it will start with Probe call.
HTTP endpoint
The external-provisioner optionally exposes an HTTP endpoint at address:port specified by --http-endpoint argument. When set, these two paths are exposed:
- Metrics path, as set by
--metrics-path argument (default is /metrics).
- Leader election health check at
/healthz/leader-election. It is recommended to run a liveness probe against this endpoint when leader election is used to kill external-provisioner leader that fails to connect to the API server to renew its leadership. See https://github.com/kubernetes-csi/csi-lib-utils/issues/66 for details.
Deployment on each node
Normally, external-provisioner is deployed once in a cluster and
communicates with a control instance of the CSI driver which then
provisions volumes via some kind of storage backend API. CSI drivers
which manage local storage on a node don’t have such an API that a
central controller could use.
To support this case, external-provisioner can be deployed alongside
each CSI driver on different nodes. The CSI driver deployment must:
- support topology, usually with one topology key
(“csi.example.org/node”) and the Kubernetes node name as value
- use a service account that has the same RBAC rules as for a normal
deployment
- invoke external-provisioner with
--node-deployment
- tweak
--node-deployment-base-delay and --node-deployment-max-delay
to match the expected cluster size and desired response times
(only relevant when there are storage classes with immediate binding,
see below for details)
- set the
NODE_NAME environment variable to the name of the Kubernetes node
- implement
GetCapacity
Usage of --strict-topology and --immediate-topology=false is
recommended because it makes the CreateVolume invocations simpler.
Topology information is always derived exclusively from the
information returned by the CSI driver that runs on the same node,
without combining that with information stored for other nodes. This
works as long as each node is in its own topology segment,
i.e. usually with a single topology key and one unique value for each
node.
Volume provisioning with late binding works as before, except that
each external-provisioner instance checks the “selected node”
annotation and only creates volumes if that node is the one it runs
on. It also only deletes volumes on its own node.
Immediate binding is also supported, but not recommended. It is
implemented by letting the external-provisioner instances assign a PVC
to one of them: when they see a new PVC with immediate binding, they
all attempt to set the “selected node” annotation with their own node
name as value. Only one update request can succeed, all others get a
“conflict” error and then know that some other instance was faster. To
avoid the thundering herd problem, each instance waits for a random
period before issuing an update request.
When CreateVolume call fails with ResourcesExhausted, the normal
recovery mechanism is used, i.e. the external-provisioner instance
removes the “selected node” annotation and the process repeats. But
this triggers events for the PVC and delays volume creation, in
particular when storage is exhausted on most nodes. Therefore
external-provisioner checks with GetCapacity before attempting to
own a PVC whether the currently available capacity is sufficient for
the volume. When it isn’t, the PVC is ignored and some other instance
can own it.
The --node-deployment-base-delay parameter determines the initial
wait period. It also sets the jitter, so in practice the initial wait period will be
in the range from zero to the base delay. If the value is high,
volumes with immediate binding get created more slowly. If it is low,
then the risk of conflicts while setting the “selected node”
annotation increases and the apiserver load will be higher.
There is an exponential backoff per PVC which is used for unexpected
problems. Normally, an owner for a PVC is chosen during the first
attempt, so most PVCs will use the base delays. A maximum can be set
with --node-deployment-max-delay anyway, to avoid very long delays
when something went wrong repeatedly.
During scale testing with 100 external-provisioner instances, a base
delay of 20 seconds worked well. When provisioning 3000 volumes, there
were only 500 conflicts which the apiserver handled without getting
overwhelmed. The average provisioning rate of around 40 volumes/second
was the same as with a delay of 10 seconds. The worst-case latency per
volume was probably higher, but that wasn’t measured.
Note that the QPS settings of kube-controller-manager and
external-provisioner have to be increased at the moment (Kubernetes
1.19) to provision volumes faster than around 4 volumes/second. Those
settings will eventually get replaced with flow control in the API
server
itself.
Beware that if no node has sufficient storage available, then also
no CreateVolume call is attempted and thus no events are generated
for the PVC, i.e. some other means of tracking remaining storage
capacity must be used to detect when the cluster runs out of storage.
Because PVCs with immediate binding get distributed randomly among
nodes, they get spread evenly. If that is not desirable, then it is
possible to disable support for immediate binding in distributed
provisioning with --node-deployment-immediate-binding=false and
instead implement a custom policy in a separate controller which sets
the “selected node” annotation to trigger local provisioning on the
desired node.
Deleting local volumes after a node failure or removal
When a node with local volumes gets removed from a cluster before
deleting those volumes, the PV and PVC objects may still exist. It may
be possible to remove the PVC normally if the volume was not in use by
any pod on the node, but normal deletion of the volume and thus
deletion of the PV is not possible anymore because the CSI driver
instance on the node is not available or reachable anymore and therefore
Kubernetes cannot be sure that it is okay to remove the PV.
When an administrator is sure that the node is never going to come
back, then the local volumes can be removed manually:
- force-delete objects:
kubectl delete pv <pv> --wait=false --grace-period=0 --force
- remove all finalizers:
kubectl patch pv <pv> -p '{"metadata":{"finalizers":null}}'
It may also be necessary to scrub disks before reusing them because
the CSI driver had no chance to do that.
If there still was a PVC which was bound to that PV, it then will be
moved to phase “Lost”. It has to be deleted and re-created if still
needed because no new volume will be created for it. Editing the PVC
to revert it to phase “Unbound” is not allowed by the Kubernetes
API server.
Community, discussion, contribution, and support
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