New to KubeDB? Please start here.

Using Custom Configuration File

KubeDB supports providing custom configuration for MongoDB. This tutorial will show you how to use KubeDB to run a MongoDB database with custom configuration.

Before You Begin

  • At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube.

  • Now, install KubeDB cli on your workstation and KubeDB operator in your cluster following the steps here.

  • To keep things isolated, this tutorial uses a separate namespace called demo throughout this tutorial. Run the following command to prepare your cluster for this tutorial:

    $ kubectl create ns demo
    namespace/demo created

Note: The yaml files used in this tutorial are stored in docs/examples/mongodb folder in GitHub repository kubedb/docs.


MongoDB allows to configure database via configuration file. The default configuration file for MongoDB deployed by KubeDB can be found in /data/configdb/mongod.conf. When MongoDB starts, it will look for custom configuration file in /configdb-readonly/mongod.conf. If configuration file exist, this custom configuration will overwrite the existing default one.

To learn available configuration option of MongoDB see Configuration File Options.

At first, you have to create a config file named mongod.conf. Then you have to put this file into a volume. You have to specify this volume in spec.configSource section while creating MongoDB crd. KubeDB will mount this volume into /configdb-readonly/ directory of the database pod.

In this tutorial, we will configure net.maxIncomingConnections (default value: 65536) via a custom config file. We will use configMap as volume source.

Custom Configuration

At first, create mongod.conf file containing required configuration settings.

$ cat mongod.conf
   maxIncomingConnections: 10000

Here, maxIncomingConnections is set to 10000, whereas the default value is 65536.

Now, create a configMap with this configuration file.

$ kubectl create configmap -n demo mg-custom-config --from-file=./mongod.conf
configmap/mg-custom-config created

Verify the config map has the configuration file.

$  kubectl get configmap -n demo mg-custom-config -o yaml
apiVersion: v1
  mongod.conf: |+
       maxIncomingConnections: 10000
kind: ConfigMap
  creationTimestamp: "2019-02-06T10:03:45Z"
  name: mg-custom-config
  namespace: demo
  resourceVersion: "91905"
  selfLink: /api/v1/namespaces/demo/configmaps/mg-custom-config
  uid: 7da0467c-29f6-11e9-aebf-080027875192

Now, create MongoDB crd specifying spec.configSource field.

kind: MongoDB
  name: mgo-custom-config
  namespace: demo
  version: "3.4-v3"
  storageType: Durable
    storageClassName: "standard"
    - ReadWriteOnce
        storage: 1Gi
        name: mg-custom-config
$ kubectl create -f created

Now, wait a few minutes. KubeDB operator will create necessary PVC, statefulset, services, secret etc. If everything goes well, we will see that a pod with the name mgo-custom-config-0 has been created.

Check that the statefulset’s pod is running

$ kubectl get pod -n demo mgo-custom-config-0
NAME                  READY     STATUS    RESTARTS   AGE
mgo-custom-config-0   1/1       Running   0          1m

Now, we will check if the database has started with the custom configuration we have provided.

Now, you can connect to this database through mongo-shell. In this tutorial, we are connecting to the MongoDB server from inside the pod.

$ kubectl get secrets -n demo mgo-custom-config-auth -o jsonpath='{.data.\username}' | base64 -d

$ kubectl get secrets -n demo mgo-custom-config-auth -o jsonpath='{.data.\password}' | base64 -d

$ kubectl exec -it mgo-custom-config-0 -n demo sh

> mongo admin

> db.auth("root","ErialNojWParBFoP")

> db._adminCommand( {getCmdLineOpts: 1})
	"argv" : [
	"parsed" : {
		"config" : "/data/configdb/mongod.conf",
		"net" : {
			"bindIp" : "",
			"maxIncomingConnections" : 10000,
			"port" : 27017
		"security" : {
			"authorization" : "enabled"
		"storage" : {
			"dbPath" : "/data/db"
	"ok" : 1

> exit

As we can see from the configuration of running mongodb, the value of maxIncomingConnections has been set to 10000 successfully.

Cleaning up

To cleanup the Kubernetes resources created by this tutorial, run:

kubectl patch -n demo mg/mgo-custom-config -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
kubectl delete -n demo mg/mgo-custom-config

kubectl patch -n demo drmn/mgo-custom-config -p '{"spec":{"wipeOut":true}}' --type="merge"
kubectl delete -n demo drmn/mgo-custom-config

kubectl delete -n demo configmap mg-custom-config

kubectl delete ns demo

Next Steps