Asked 1 month ago by UranianNavigator823
How can I avoid LevelDB lock errors when multiple Kubernetes pods share an NFS volume?
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I'm running two Kubernetes (v1.30.x) pods that mount the same NFS (v4) folder, but one pod fails with a lock error from LevelDB. The error output is as follows:
BASH│ Persisting documents to "/opt/data/yjs-storage" │ │ /home/node/app/node_modules/levelup/lib/levelup.js:119 │ return callback(new OpenError(err)) │ ^ │ Error [OpenError]: IO error: lock /opt/data/yjs-storage/LOCK: Resource temporarily unavailable │ at /home/node/app/node_modules/levelup/lib/levelup.js:119:23 │ at /home/node/app/node_modules/abstract-leveldown/abstract-leveldown.js:38:14 │ at /home/node/app/node_modules/deferred-leveldown/deferred-leveldown.js:31:21 │ at /home/node/app/node_modules/abstract-leveldown/abstract-leveldown.js:38:14 │ at /home/node/app/node_modules/abstract-leveldown/abstract-leveldown.js:38:14 │ Emitted 'error' event on LevelUP instance at: │ at /home/node/app/node_modules/levelup/lib/levelup.js:60:19 │ at /home/node/app/node_modules/levelup/lib/levelup.js:119:14 │ at /home/node/app/node_modules/abstract-leveldown/abstract-leveldown.js:38:14 │ [... lines matching original stack trace ...] │ at /home/node/app/node_modules/abstract-leveldown/abstract-leveldown.js:38:14 { │ [cause]: undefined │ } │ │ Node.js v18.20.6
The NFS persistent volume is set up as shown below:
apiVersion: v1
kind: PersistentVolume
metadata:
name: nfs-texhub-server-pv-qingdao
spec:
capacity:
storage: 8Gi
nfs:
server: 60cw9b7f-osv72.cn-qingdao.nas.aliyuncs.com
path: /k8s/reddwarf-pro/texhub-server-service
accessModes:
- ReadWriteMany
claimRef:
kind: PersistentVolumeClaim
namespace: reddwarf-pro
name: texhub-server-service-pv-claim-qingdao
uid: 926e70a4-651f-467a-9a81-0b87a7b696ee
apiVersion: v1
resourceVersion: '1080096'
persistentVolumeReclaimPolicy: Retain
mountOptions:
- vers=4.0
- noresvport
volumeMode: Filesystem
It seems that while NFS supports multiple writers in ReadWriteMany mode, LevelDB itself is not designed for concurrent access from multiple processes since it tries to acquire an exclusive lock on a file. I would like to know if it is possible to enable multiple pods to write to the same NFS directory and what approaches or workarounds (such as using separate directories, a different database, or distributed locking) might resolve this issue.
Please advise on how best to handle this scenario.
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2 Answers
Answer by 
TychoAI Agent • 1 month ago
0
The Kubernetes NFS volume is designed to allow multiple pods to mount the same share simultaneously (using access mode ReadWriteMany). In your case, the error indicates that your application—in this instance, LevelDB—is running into a file locking conflict when two processes try to access the same file concurrently.
Here are a few points to consider:
-
NFS Capability:
NFS itself supports multiple writers. Your PersistentVolume is correctly configured with ReadWriteMany and the appropriate mount options for NFSv4. -
Application-Level Locking:
The error message, "IO error: lock /opt/data/yjs-storage/LOCK: Resource temporarily unavailable", suggests that LevelDB is attempting to acquire an exclusive lock on a file that is already in use. Many single-instance databases or file-based storage systems are not designed for concurrent writers across multiple processes. Check whether LevelDB supports multi-process concurrency or if you need to configure each pod to use a separate directory. -
Possible Solutions:
- Use Separate Directories: If LevelDB doesn’t support concurrent access via file locks over NFS, consider configuring each pod to write to its own subdirectory rather than sharing the exact same directory.
- Use a Different Storage Approach: Consider using a clustered database or another storage backend that supports concurrent writes from multiple clients.
- Application Coordination: If sharing the same directory is necessary, you may need to implement a form of distributed locking or coordination rather than relying on file locks provided by LevelDB.
In summary, Kubernetes and NFS allow multiple pods to mount and write to the same volume, but your application must reliably handle concurrent access. This error is not due to the Kubernetes configuration but rather how the underlying application (or library) manages file locks.
Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?
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Answer by AstralTraveler239 • 1 month ago
0
The error you are seeing suggests that the NFS mount is being used by several processes at once and that there is a locking problem on the NFS server, as stated in the comments.
Please be noted that LevelDB is designed to be used by a single process at a time. When you are trying for multiple processes this could also be done by using kubernetes mechanisms like Pod Affinity or Pod Anti-Affinity to make sure that only one pod can access the database at a time.
Adding to that you can also use the Pod Topology Spread Constraints which might help to resolve the constraint issue.
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