MongoDB Helm Chart

Prerequisites Details

Kubernetes 1.6+ with Beta APIs enabled.
PV support on the underlying infrastructure.

StatefulSet Details

https://kubernetes.io/docs/concepts/abstractions/controllers/statefulsets/

StatefulSet Caveats

https://kubernetes.io/docs/concepts/abstractions/controllers/statefulsets/#limitations

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
`replicaSet`	Name of the replica set	rs0
`replicas`	Number of replicas in the replica set	3
`port`	MongoDB port	27017
`installImage.name`	Image name for the init container that establishes the replica set	gcr.io/google_containers/mongodb-install
`installImage.tag`	Image tag for the init container that establishes the replica set	0.3
`installImage.pullPolicy`	Image pull policy for the init container that establishes the replica set	IfNotPresent
`image.name`	MongoDB image name	mongo
`image.tag`	MongoDB image tag	3.4
`image.pullPolicy`	MongoDB image pull policy	IfNotPresent
`metrics.enabled`	If `true`, Prometheus metrics exporter is enabled	`false`
`metrics.image`	Image name for the metrics exporter container	reactioncommerce/mongdb_exporter
`metrics.imageTag`	Image tag for the metrics exporter container	v1.1.0
`metrics.imagePullPolicy`	Image pull policy for the metrics exporter container	IfNotPresent
`metrics.port`	Metrics port	9001
`metrics.serviceLabels`	Additional labels applied if metrics enabled is `true`	{}
`metrics.env.MONGODB_URL`	Custom metrics MongoDB URL, provided to customize connection params	mongodb://127.0.0.1:27017
`podAnnotations`	Annotations to be added to MongoDB pods	{}
`resources`	Pod resource requests and limits	{}
`persistentVolume.enabled`	If `true`, persistent volume claims are created	`true`
`persistentVolume.storageClass`	Persistent volume storage class	`volume.alpha.kubernetes.io/storage-class: default`
`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	See below
`nodeSelector`	Node labels for pod assignment	{}

MongoDB config file

The MongoDB config file mongod.conf is configured via the configmap configuration value. The defaults from values.yaml are the following:

configmap:
  storage:
    dbPath: /data/db
  net:
    port: 27017
  replication:
    replSetName: rs0

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.

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')"

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: 3.4.5
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.4.5
{
	"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: 3.4.5
connecting to: mongodb://127.0.0.1:27017
{ "nInserted" : 1 }

Watch existing members:

$ kubectl run --attach bbox --image=mongo:3.4 --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: 3.4.5
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.

Metrics

The chart optionally can start a metrics exporter for prometheus. The metrics endpoint (port 9001) is exposed in the service. Metrics can be scraped from within the cluster using something similar as the described in the example Prometheus scrape configuration. Custom labels may be applied using the metrics.serviceLabels value for monitoring with Prometheus-Operator.

Name		Name	Last commit message	Last commit date
Latest commit History 29 Commits
.circleci		.circleci
mongodb-replicaset		mongodb-replicaset
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md

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MongoDB Helm Chart

Prerequisites Details

StatefulSet Details

StatefulSet Caveats

Chart Details

Installing the Chart

Configuration

Authentication

TLS support

Deep dive

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Failover

Scaling

Metrics

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MongoDB Helm Chart

Prerequisites Details

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Installing the Chart

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Authentication

TLS support

Deep dive

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Failover

Scaling

Metrics

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