TL DR
mongod --wiredTigerCacheSizeGB 0.25 --replSet rs0 --keyFile /data/db/security.keyFile ignored replSet param on initial run (means there no /data/db folder yet) in docker container, as running in js script rs.initiate() command showing following non-fatal error in mongod logs
```
MongoDB server version: 4.4.4

{     "ok" : 0,     "errmsg" : "This node was not started with the replSet option",     "code" : 76,     "codeName" : "NoReplicationEnabled" }

```
Also mongod logs showing following for cli params passed
```
Options set by command line","attr":{"options":{"net":{"bindIp":"127.0.0.1","port":27017,"tls":{"mode":"disabled"}},"processManagement":{"fork":true,"pidFilePath":"/tmp/docker-entrypoint-temp-mongod.pid"},"security":{"keyFile":"/data/db/security.keyFile"},"storage":{"wiredTiger":{"engineConfig":

{"cacheSizeGB":0.25}

}},"systemLog":{"destination":"file","logAppend":true,"path":"/proc/1/fd/1"}}}}
```

Using following manifests:
```
apiVersion: v1
kind: Service
metadata:
  name: mongo
  labels:
    app: mongo
spec:
  ports:
  - port: 27017
  selector:
    app: mongo
—
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongo
  namespace: default
spec:
  replicas: 1
  revisionHistoryLimit: 1
  strategy:
    type: Recreate
  selector:
    matchLabels:
      app: mongo
  template:
    metadata:
      labels:
        app: mongo
        tier: base
    spec:
      hostNetwork: true
      dnsPolicy: ClusterFirstWithHostNet
      containers:
      - name: mongo
        image: mongo:4.4.4-bionic
        args:
          - "--wiredTigerCacheSizeGB"
          - "0.25"
          - "--replSet"
          - "rs0"
          - "--keyFile"
          - "/data/db/security.keyFile"
        ports:
        - containerPort: 27017
        volumeMounts:
        - name: data
          mountPath: /data/db
        - name: entrypoint
          mountPath: /docker-entrypoint-initdb.d/
        env:
          - name: MONGO_INITDB_DATABASE
            valueFrom:
              configMapKeyRef:
                key: MONGO_DB
                name: envars
          - name: MONGO_INITDB_ROOT_USERNAME
            valueFrom:
              secretKeyRef:
                key: MONGO_USER
                name: sealed-secrets
          - name: MONGO_INITDB_ROOT_PASSWORD
            valueFrom:
              secretKeyRef:
                key: MONGO_PASS
                name: sealed-secrets
      volumes:
      - name: data
        hostPath:
          path: /data/mongodata
          type: DirectoryOrCreate
      - name: entrypoint
        secret:
          secretName: mongo-init
```
mongo-init secret value is
#/bin/bash

sleep 10s
mongo -u ${MONGO_INITDB_ROOT_USERNAME} -p ${MONGO_INITDB_ROOT_PASSWORD} <<EOF
rs.initiate()
EOF

sleep 10s