MongoDb in GCE - Limiting memory on insert

[Boas Enkler]

In googles Kubernetes we ha mongodb running. A api is currently offering a method which is recevieng databatches which should be inserted in the mongodb,

The mongodb runs in kubernetes on 3 Nodes. each having 3.75 GB memory. 

Now it happens very often then when running such a batch import that we run into out of memory issues.

The cluster tried to allocate about 8GB of RAM.

The question is what is the correct way to limit the memory usage? The batch import isn't that performance critical. 

We set the wiredTigerCacheSizeGB to 1.5 (GB) but this didn't help.

Our code inserting the data looks like this:

            IMongoCollection<T> stageCollection = Database.GetCollection<T>(StageName);

            foreach (var batch in entites.Batch(1000))

            {

                await stageCollection.InsertManyAsync(batch);

            }

There is one unique combined index like this:

collection.Indexes.CreateOneAsync(IndexKeys

                    .Ascending(x => x.DepatureCityId)

                    .Ascending(x => x.ArrivalCityId),

                new CreateIndexOptions

                {

                    Unique = true,

                    Background = true

                });

Is there anyadvice on how to limit the memory so that our nodes don't run im ooms?

Here our yaml configuration for the mongodatabase

---
	kind: StorageClass
	apiVersion: storage.k8s.io/v1
	metadata:
	name: fast
	provisioner: kubernetes.io/gce-pd
	parameters:
	type: pd-ssd
	---
	apiVersion: v1
	kind: Service
	metadata:
	name: mongo
	labels:
	name: mongo
	spec:
	ports:
	- port: 27017
	targetPort: 27017
	clusterIP: None
	selector:
	role: mongo
	---
	apiVersion: apps/v1beta1
	kind: StatefulSet
	metadata:
	name: mongo
	spec:
	serviceName: "mongo"
	replicas: 3
	template:
	metadata:
	labels:
	role: mongo
	environment: test
	spec:
	terminationGracePeriodSeconds: 10
	containers:
	- name: mongo
	image: mongo:3.6
	command:
	- mongod
	- "--replSet"
	- rs0
	- "--bind_ip"
	- "0.0.0.0"
	- "--noprealloc"
	- "--wiredTigerCacheSizeGB"
	- "1.5"
	ports:
	- containerPort: 27017
	volumeMounts:
	- name: mongo-persistent-storage
	mountPath: /data/db
	- name: mongo-sidecar
	image: cvallance/mongo-k8s-sidecar
	env:
	- name: MONGO_SIDECAR_POD_LABELS
	value: "role=mongo,environment=test"
	volumeClaimTemplates:
	- metadata:
	name: mongo-persistent-storage
	annotations:
	volume.beta.kubernetes.io/storage-class: "fast"
	spec:
	accessModes: [ "ReadWriteOnce" ]
	resources:
	requests:
	storage: 32Gi

[Boas Enkler]

In the meanwhile i also set the pod antiaffinity to other pods make sure that no other pod is running on the given node.