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README.md

MongoDB Helm Chart

Prerequisites Details

  • Kubernetes 1.8+ with Beta APIs enabled.
  • PV support on the underlying infrastructure.

StatefulSet Details

StatefulSet Caveats

Chart Details

This chart implements a dynamically scalable MongoDB replica set using Kubernetes StatefulSets and Init Containers.

Installing the Chart

To install the chart with the release name my-release:

$ helm repo add stable https://kubernetes-charts.storage.googleapis.com/
$ helm install --name my-release stable/mongodb-replicaset

Configuration

The following tables lists the configurable parameters of the mongodb chart and their default values.

Parameter Description Default
replicas Number of replicas in the replica set 3
replicaSetName The name of the replica set rs0
podDisruptionBudget Pod disruption budget {}
port MongoDB port 27017
installImage.repository Image name for the install container k8s.gcr.io/mongodb-install
installImage.tag Image tag for the install container 0.5
installImage.pullPolicy Image pull policy for the init container that establishes the replica set IfNotPresent
image.repository MongoDB image name mongo
image.tag MongoDB image tag 3.6
image.pullPolicy MongoDB image pull policy IfNotPresent
podAnnotations Annotations to be added to MongoDB pods {}
securityContext Security context for the pod {runAsUser: 999, fsGroup: 999, runAsNonRoot: true}
resources Pod resource requests and limits {}
persistentVolume.enabled If true, persistent volume claims are created true
persistentVolume.storageClass Persistent volume storage class ``
persistentVolume.accessMode Persistent volume access modes [ReadWriteOnce]
persistentVolume.size Persistent volume size 10Gi
persistentVolume.annotations Persistent volume annotations {}
tls.enabled Enable MongoDB TLS support including authentication false
tls.cacert The CA certificate used for the members Our self signed CA certificate
tls.cakey The CA key used for the members Our key for the self signed CA certificate
auth.enabled If true, keyfile access control is enabled false
auth.key Key for internal authentication ``
auth.existingKeySecret If set, an existing secret with this name for the key is used ``
auth.adminUser MongoDB admin user ``
auth.adminPassword MongoDB admin password ``
auth.existingAdminSecret If set, and existing secret with this name is used for the admin user ``
serviceAnnotations Annotations to be added to the service {}
configmap Content of the MongoDB config file ``
nodeSelector Node labels for pod assignment {}
affinity Node/pod affinities {}
tolerations List of node taints to tolerate []
livenessProbe Liveness probe configuration See below
readinessProbe Readiness probe configuration See below
extraVars Set environment variables for the main container {}

MongoDB config file

All options that depended on the chart configuration are supplied as command-line arguments to mongod. By default, the chart creates an empty config file. Entries may be added via the configmap configuration value.

Specify each parameter using the --set key=value[,key=value] argument to helm install.

Alternatively, a YAML file that specifies the values for the parameters can be provided while installing the chart. For example,

$ helm install --name my-release -f values.yaml stable/mongodb-replicaset

Tip

: You can use the default values.yaml

Once you have all 3 nodes in running, you can run the "test.sh" script in this directory, which will insert a key into the primary and check the secondaries for output. This script requires that the $RELEASE_NAME environment variable be set, in order to access the pods.

Authentication

By default, this chart creates a MongoDB replica set without authentication. Authentication can be enabled using the parameter auth.enabled. Once enabled, keyfile access control is set up and an admin user with root privileges is created. User credentials and keyfile may be specified directly. Alternatively, existing secrets may be provided. The secret for the admin user must contain the keys user and password, that for the key file must contain key.txt. The user is created with full root permissions but is restricted to the admin database for security purposes. It can be used to create additional users with more specific permissions.

TLS support

To enable full TLS encryption set tls.enabled to true. It is recommended to create your own CA by executing:

$ openssl genrsa -out ca.key 2048
$ openssl req -x509 -new -nodes -key ca.key -days 10000 -out ca.crt -subj "/CN=mydomain.com"

After that paste the base64 encoded (cat ca.key | base64 -w0) cert and key into the fields tls.cacert and tls.cakey. Adapt the configmap for the replicaset as follows:

configmap:
  storage:
    dbPath: /data/db
  net:
    port: 27017
    ssl:
      mode: requireSSL
      CAFile: /ca/tls.crt
      PEMKeyFile: /work-dir/mongo.pem
  replication:
    replSetName: rs0
  security:
    authorization: enabled
    clusterAuthMode: x509
    keyFile: /keydir/key.txt

To access the cluster you need one of the certificates generated during cluster setup in /work-dir/mongo.pem of the certain container or you generate your own one via:

$ cat >openssl.cnf <<EOL
[req]
req_extensions = v3_req
distinguished_name = req_distinguished_name
[req_distinguished_name]
[ v3_req ]
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectAltName = @alt_names
[alt_names]
DNS.1 = $HOSTNAME1
DNS.1 = $HOSTNAME2
EOL
$ openssl genrsa -out mongo.key 2048
$ openssl req -new -key mongo.key -out mongo.csr -subj "/CN=$HOSTNAME" -config openssl.cnf
$ openssl x509 -req -in mongo.csr \
    -CA $MONGOCACRT -CAkey $MONGOCAKEY -CAcreateserial \
    -out mongo.crt -days 3650 -extensions v3_req -extfile openssl.cnf
$ rm mongo.csr
$ cat mongo.crt mongo.key > mongo.pem
$ rm mongo.key mongo.crt

Please ensure that you exchange the $HOSTNAME with your actual hostname and the $HOSTNAME1, $HOSTNAME2, etc. with alternative hostnames you want to allow access to the MongoDB replicaset. You should now be able to authenticate to the mongodb with your mongo.pem certificate:

$ mongo --ssl --sslCAFile=ca.crt --sslPEMKeyFile=mongo.pem --eval "db.adminCommand('ping')"

Readiness probe

The default values for the readiness probe are:

readinessProbe:
  initialDelaySeconds: 5
  timeoutSeconds: 1
  failureThreshold: 3
  periodSeconds: 10
  successThreshold: 1

Liveness probe

The default values for the liveness probe are:

livenessProbe:
  initialDelaySeconds: 30
  timeoutSeconds: 5
  failureThreshold: 3
  periodSeconds: 10
  successThreshold: 1

Deep dive

Because the pod names are dependent on the name chosen for it, the following examples use the environment variable RELEASENAME. For example, if the helm release name is messy-hydra, one would need to set the following before proceeding. The example scripts below assume 3 pods only.

export RELEASE_NAME=messy-hydra

Cluster Health

$ for i in 0 1 2; do kubectl exec $RELEASE_NAME-mongodb-replicaset-$i -- sh -c 'mongo --eval="printjson(db.serverStatus())"'; done

Failover

One can check the roles being played by each node by using the following:

$ for i in 0 1 2; do kubectl exec $RELEASE_NAME-mongodb-replicaset-$i -- sh -c 'mongo --eval="printjson(rs.isMaster())"'; done

MongoDB shell version: 3.6.3
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.6.3
{
	"hosts" : [
		"messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
		"messy-hydra-mongodb-1.messy-hydra-mongodb.default.svc.cluster.local:27017",
		"messy-hydra-mongodb-2.messy-hydra-mongodb.default.svc.cluster.local:27017"
	],
	"setName" : "rs0",
	"setVersion" : 3,
	"ismaster" : true,
	"secondary" : false,
	"primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
	"me" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
	"electionId" : ObjectId("7fffffff0000000000000001"),
	"maxBsonObjectSize" : 16777216,
	"maxMessageSizeBytes" : 48000000,
	"maxWriteBatchSize" : 1000,
	"localTime" : ISODate("2016-09-13T01:10:12.680Z"),
	"maxWireVersion" : 4,
	"minWireVersion" : 0,
	"ok" : 1
}

This lets us see which member is primary.

Let us now test persistence and failover. First, we insert a key (in the below example, we assume pod 0 is the master):

$ kubectl exec $RELEASE_NAME-mongodb-replicaset-0 -- mongo --eval="printjson(db.test.insert({key1: 'value1'}))"

MongoDB shell version: 3.6.3
connecting to: mongodb://127.0.0.1:27017
{ "nInserted" : 1 }

Watch existing members:

$ kubectl run --attach bbox --image=mongo:3.6 --restart=Never --env="RELEASE_NAME=$RELEASE_NAME" -- sh -c 'while true; do for i in 0 1 2; do echo $RELEASE_NAME-mongodb-replicaset-$i $(mongo --host=$RELEASE_NAME-mongodb-replicaset-$i.$RELEASE_NAME-mongodb-replicaset --eval="printjson(rs.isMaster())" | grep primary); sleep 1; done; done';

Waiting for pod default/bbox2 to be running, status is Pending, pod ready: false
If you don't see a command prompt, try pressing enter.
messy-hydra-mongodb-2 "primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
messy-hydra-mongodb-0 "primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
messy-hydra-mongodb-1 "primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
messy-hydra-mongodb-2 "primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
messy-hydra-mongodb-0 "primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",

Kill the primary and watch as a new master getting elected.

$ kubectl delete pod $RELEASE_NAME-mongodb-replicaset-0

pod "messy-hydra-mongodb-0" deleted

Delete all pods and let the statefulset controller bring it up.

$ kubectl delete po -l "app=mongodb-replicaset,release=$RELEASE_NAME"
$ kubectl get po --watch-only
NAME                    READY     STATUS        RESTARTS   AGE
messy-hydra-mongodb-0   0/1       Pending   0         0s
messy-hydra-mongodb-0   0/1       Pending   0         0s
messy-hydra-mongodb-0   0/1       Pending   0         7s
messy-hydra-mongodb-0   0/1       Init:0/2   0         7s
messy-hydra-mongodb-0   0/1       Init:1/2   0         27s
messy-hydra-mongodb-0   0/1       Init:1/2   0         28s
messy-hydra-mongodb-0   0/1       PodInitializing   0         31s
messy-hydra-mongodb-0   0/1       Running   0         32s
messy-hydra-mongodb-0   1/1       Running   0         37s
messy-hydra-mongodb-1   0/1       Pending   0         0s
messy-hydra-mongodb-1   0/1       Pending   0         0s
messy-hydra-mongodb-1   0/1       Init:0/2   0         0s
messy-hydra-mongodb-1   0/1       Init:1/2   0         20s
messy-hydra-mongodb-1   0/1       Init:1/2   0         21s
messy-hydra-mongodb-1   0/1       PodInitializing   0         24s
messy-hydra-mongodb-1   0/1       Running   0         25s
messy-hydra-mongodb-1   1/1       Running   0         30s
messy-hydra-mongodb-2   0/1       Pending   0         0s
messy-hydra-mongodb-2   0/1       Pending   0         0s
messy-hydra-mongodb-2   0/1       Init:0/2   0         0s
messy-hydra-mongodb-2   0/1       Init:1/2   0         21s
messy-hydra-mongodb-2   0/1       Init:1/2   0         22s
messy-hydra-mongodb-2   0/1       PodInitializing   0         25s
messy-hydra-mongodb-2   0/1       Running   0         26s
messy-hydra-mongodb-2   1/1       Running   0         30s


...
messy-hydra-mongodb-0 "primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
messy-hydra-mongodb-1 "primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",
messy-hydra-mongodb-2 "primary" : "messy-hydra-mongodb-0.messy-hydra-mongodb.default.svc.cluster.local:27017",

Check the previously inserted key:

$ kubectl exec $RELEASE_NAME-mongodb-replicaset-1 -- mongo --eval="rs.slaveOk(); db.test.find({key1:{\$exists:true}}).forEach(printjson)"

MongoDB shell version: 3.6.3
connecting to: mongodb://127.0.0.1:27017
{ "_id" : ObjectId("57b180b1a7311d08f2bfb617"), "key1" : "value1" }

Scaling

Scaling should be managed by helm upgrade, which is the recommended way.

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