Kubernetes的Local Path Provisioner

Local Path Provisioner

Use HostPath for persistent local storage with Kubernetes.

Overview

Local Path Provisioner provides a way for the Kubernetes users to utilize the local storage in each node. Based on the user configuration, the Local Path Provisioner will create hostPath based persistent volume on the node automatically. It utilizes the features introduced by Kubernetes Local Persistent Volume feature, but make it a simpler solution than the built-in local volume feature in Kubernetes.

Compare to built-in Local Persistent Volume feature in Kubernetes

 

Pros

Dynamic provisioning the volume using host path.

• Currently the Kubernetes Local Volume provisioner cannot do dynamic provisioning for the host path volumes.

 

Cons

1. No support for the volume capacity limit currently.
   1. The capacity limit will be ignored for now.
2. Only support hostPath

 

Requirement

Kubernetes v1.12+.

 

Deployment

 

Installation

In this setup, the directory /opt/local-path-provisioner will be used across all the nodes as the path for provisioning (a.k.a, store the persistent volume data). The provisioner will be installed in local-path-storage namespace by default.

kubectl apply -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/deploy/local-path-storage.yaml

After installation, you should see something like the following:

$ kubectl -n local-path-storage get pod
NAME                                     READY     STATUS    RESTARTS   AGE
local-path-provisioner-d744ccf98-xfcbk   1/1       Running   0          7m

Check and follow the provisioner log using:

$ kubectl -n local-path-storage logs -f local-path-provisioner-d744ccf98-xfcbk

 

Usage

Create a hostPath backed Persistent Volume and a pod uses it:

kubectl create -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/examples/pvc.yaml
kubectl create -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/examples/pod.yaml

You should see the PV has been created:

$ kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                    STORAGECLASS   REASON    AGE
pvc-bc3117d9-c6d3-11e8-b36d-7a42907dda78   2Gi        RWO            Delete           Bound     default/local-path-pvc   local-path               4s

The PVC has been bound:

$ kubectl get pvc
NAME             STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
local-path-pvc   Bound     pvc-bc3117d9-c6d3-11e8-b36d-7a42907dda78   2Gi        RWO            local-path     16s

And the Pod started running:

$ kubectl get pod
NAME          READY     STATUS    RESTARTS   AGE
volume-test   1/1       Running   0          3s

Write something into the pod

kubectl exec volume-test -- sh -c "echo local-path-test > /data/test"

Now delete the pod using

kubectl delete -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/examples/pod.yaml

After confirm that the pod is gone, recreated the pod using

kubectl create -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/examples/pod.yaml

Check the volume content:

$ kubectl exec volume-test cat /data/test
local-path-test

Delete the pod and pvc

kubectl delete -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/examples/pod.yaml
kubectl delete -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/examples/pvc.yaml

The volume content stored on the node will be automatically cleaned up. You can check the log of local-path-provisioner-xxx for details.

Now you've verified that the provisioner works as expected.

 

Configuration

The configuration of the provisioner is a json file config.json, stored in the a config map, e.g.:

kind: ConfigMap
apiVersion: v1
metadata:
  name: local-path-config
  namespace: local-path-storage
data:
  config.json: |-
        {
                "nodePathMap":[
                {
                        "node":"DEFAULT_PATH_FOR_NON_LISTED_NODES",
                        "paths":["/opt/local-path-provisioner"]
                },
                {
                        "node":"yasker-lp-dev1",
                        "paths":["/opt/local-path-provisioner", "/data1"]
                },
                {
                        "node":"yasker-lp-dev3",
                        "paths":[]
                }
                ]
        }

 

Definition

nodePathMap is the place user can customize where to store the data on each node.

1. If one node is not listed on the nodePathMap, and Kubernetes wants to create volume on it, the paths specified in DEFAULT_PATH_FOR_NON_LISTED_NODES will be used for provisioning.
2. If one node is listed on the nodePathMap, the specified paths in paths will be used for provisioning.
   1. If one node is listed but with paths set to [], the provisioner will refuse to provision on this node.
   2. If more than one path was specified, the path would be chosen randomly when provisioning.

 

Rules

The configuration must obey following rules:

1. config.json must be a valid json file.
2. A path must start with /, a.k.a an absolute path.
3. Root directory(/) is prohibited.
4. No duplicate paths allowed for one node.
5. No duplicate node allowed.

 

Reloading

The provisioner supports automatic configuration reloading. Users can change the configuration using kubectl apply or kubectl edit with config map local-path-config. There is a delay between when the user updates the config map and the provisioner picking it up.

When the provisioner detects the configuration changes, it will try to load the new configuration. Users can observe it in the log

time="2018-10-03T05:56:13Z" level=debug msg="Applied config: {"nodePathMap":[{"node":"DEFAULT_PATH_FOR_NON_LISTED_NODES","paths":["/opt/local-path-provisioner"]},{"node":"yasker-lp-dev1","paths":["/opt","/data1"]},{"node":"yasker-lp-dev3"}]}"

If the reload fails, the provisioner will log the error and continue using the last valid configuration for provisioning in the meantime.

time="2018-10-03T05:19:25Z" level=error msg="failed to load the new config file: fail to load config file /etc/config/config.json: invalid character '#' looking for beginning of object key string"

time="2018-10-03T05:20:10Z" level=error msg="failed to load the new config file: config canonicalization failed: path must start with / for path opt on node yasker-lp-dev1"

time="2018-10-03T05:23:35Z" level=error msg="failed to load the new config file: config canonicalization failed: duplicate path /data1 on node yasker-lp-dev1

time="2018-10-03T06:39:28Z" level=error msg="failed to load the new config file: config canonicalization failed: duplicate node yasker-lp-dev3"

 

Uninstall

Before uninstallation, make sure the PVs created by the provisioner have already been deleted. Use kubectl get pv and make sure no PV with StorageClass local-path.

To uninstall, execute:

kubectl delete -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/deploy/local-path-storage.yaml

 

License

Copyright (c) 2014-2018 Rancher Labs, Inc.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.