Error parsing command line: unrecognised option '--wiredTigerCacheSizeGB 2'-CodePudding

I have a Google Kubernetes Engine running and I'm trying to deploy a mongo container. Everything works fine except when I try to use the argument "--wiredTigerCacheSizeGB", then the deployment fails because this command is not recognized. I'm using the latest Mongo version (5.0) and I see nothing in the documentation saying that this should not work.

Here is the yml configuration of the POD creation:

apiVersion: apps/v1
kind: StatefulSet
spec:
  podManagementPolicy: OrderedReady
  replicas: 1
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      environment: test
      role: mongo
  serviceName: mongo
  template:
    metadata:
      creationTimestamp: null
      labels:
        environment: test
        role: mongo
      namespace: default
    spec:
      containers:
      - command:
        - mongod
        - --wiredTigerCacheSizeGB 2
        image: mongo:5.0
        imagePullPolicy: Always
        name: mongo
        ports:
        - containerPort: 27017
          protocol: TCP
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
        volumeMounts:
        - mountPath: /data/db
          name: mongo-persistent-storage
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      terminationGracePeriodSeconds: 10
      tolerations:
      - effect: NoSchedule
        key: dedicated
        operator: Equal
        value: backend
  updateStrategy:
    type: OnDelete
  volumeClaimTemplates:
  - apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      annotations:
        volume.beta.kubernetes.io/storage-class: standard
      creationTimestamp: null
      name: mongo-persistent-storage
    spec:
      accessModes:
      - ReadWriteOnce
      resources:
        requests:
          storage: 20Gi
      volumeMode: Filesystem

CodePudding user response：

Does it work if you remove the --wiredTigerCacheSizeGB flag?

~~I would be surprised.~~

It does appear to work (see below) but I can't explain why. I am surprised!

If this is the correct Dockerfile for the image, then it uses a Docker CMD to run mongod.

If so, you'd need to run the image on Kubernetes using args not command in order to correctly override the container image's CMD and not override the container image's ENTRYPOINT, i.e.

containers:
- name: mongo
  args:
  - mongod
  - --wiredTigerCacheSizeGB=2

NOTE The inclusion of = between the flag and value to avoid introducing YAML parsing issues.

I tested this hypothesis using podman; you can replace podman with docker in what follows if you use docker:

# Does not work: Override `ENTRYPOINT` with mongod flag
# This is effectively what you're doing
podman run \
--interactive --tty --rm \
--entrypoint="mongod --wiredTigerCacheSizeGB=2" \
docker.io/mongo:5.0 \
Error: executable file `mongod --wiredTigerCacheSizeGB=2` not found in $PATH:
No such file or directory:
OCI runtime attempted to invoke a command that was not found

# Works: Override `CMD`
# This is what I thought should work
podman run \
--interactive --tty --rm \
docker.io/mongo:5.0 \
  mongod \
  --wiredTigerCacheSizeGB=2

# Works: Override `ENTRYPOINT` w/ mongod
# This is what I thought wouldn't work
podman run \
--interactive --tty --rm \
--entrypoint=mongod \
docker.io/mongo:5.0 \
  --wiredTigerCacheSizeGB=2

CodePudding user response：

By default Mongo will set the wiredTigerCacheSizeGB to a value proportional to the host's total memory regardless of memory limits you may have imposed on the container. In such an instance you will want to set the cache size to something appropriate, taking into account any other processes you may be running in the container which would also utilize memory.

Taking the examples above you can configure the cache size to use 1.5GB as:

$ docker run --name some-mongo -d mongo --wiredTigerCacheSizeGB 1.5

WiredTiger Options